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Feed costs constitute a significant part of the expenses in the aquaculture industry. However, feeding practices in fish farming often rely on the breeder's experience, leading to feed wastage and environmental pollution. To achieve precision in feeding, it is crucial to adjust the feed according to the fish's feeding state. Existing computer vision-based methods for assessing feeding intensity are limited by their dependence on a single spatial feature and manual threshold setting for determining feeding status constraints. These models lack practicality due to their specificity to certain scenarios and objectives. To address these limitations, we propose an integrated approach that combines computer vision technology with a Convolutional Neural Net-work (CNN) to assess the feeding intensity of farmed fish. Our method incorporates temporal, spatial, and data statistical features to provide a comprehensive evaluation of feeding intensity. Using computer vision techniques, we preprocessed feeding images of pearl gentian grouper, extracting temporal features through optical flow, spatial features via binarization, and statistical features using the gray-level co-occurrence matrix. These features are input into their respective specific feature discrimination networks, and the classification results of the three networks are fused to construct a three-stream network for feeding intensity discrimination. The results of our proposed three-stream network achieved an impressive accuracy of 99.3% in distinguishing feeding intensity. The model accurately categorizes feeding states into none, weak, and strong, providing a scientific basis for intelligent fish feeding in aquaculture. This advancement holds promise for promoting sustainable industry development by minimizing feed wastage and optimizing environmental impact. [ABSTRACT FROM AUTHOR]

The use of nutraceuticals in aquaculture is getting attention to minimize oxidative stress and increase immunity of aquatic animals. In our experiment, we tested the potency of Phyllanthus niruri, as a stress-reducing and immune-stimulating agent in Nile tilapia, Oreochromis niloticus. We reared fish in a recirculating system for 90 days at low (5 g/L) and high (30 g/L) densities. We fed half of the low and high-density fish with commercial feed (control feed) and the other half, with 5% Phyllanthus niruri incorporated into commercial feed (supplemented feed). We assessed plasma cortisol, blood glucose, packed cell volume, plasma proteins, phagocytic capacity, respiratory burst activity, and lysozyme activity. None of these parameters showed any significant difference among the experimental groups. Based on our findings, we conclude that Phyllanthus niruri does not have any potential role in modulating stress and immune response in fish as a nutraceutical. [ABSTRACT FROM AUTHOR]

The study investigated the impact of N-acetyl cysteine on growth, immune response, and antioxidant activity in tilapia (Oreochromis niloticus). Fish were reared at three densities (1.50, 3.00, and 4.50 kg/m3) with four levels of N-acetyl cysteine supplementation (0, 2, 4, and 6 mg/kg) over 60 days. Better growth was observed at low density, but at all densities, fish fed the highest N-acetyl cysteine level (6 mg/kg) showed improved growth. Chemical composition of fish and activity of amylase, lipase and protease in all treatments were noted to be insignificant. The levels of antioxidant enzymes (catalase, superoxide dismutase and glutathione peroxidase) and cortisol in HD treatments were high as compared to LD and MD treatment. However, fish fed with N3 diet in each density treatment showed the lowest level of antioxidant enzymes as well as cortisol. Similarly, the levels of malondialdehyde were noted to be high at HD treatments as compared to that in LD and MD. Its levels were lower in fish fed with N3 diets in all density treatments. Expression of somatostatins-1 did not increase in MD and HD treatments in response to high stocking density when compared with LD treatment. However, pro-opiomelanocortin-α level was reduced after N3 diet in HD treatment and interleukin 1-β expression increased after N3 supplement in HD treatment. In conclusion, N-acetyl cysteine supplementation improved growth and antioxidant response in tilapia. The most optimum dose of N-acetyl cysteine was noted to be 6 mg/kg at high stocking, suggesting the potential role of this nutraceutical in tilapia intensive culture. [ABSTRACT FROM AUTHOR]

The use of anesthetic agents in the management of fish in fish farming or ornamental fish breeding aims to minimize stress and promote animal welfare. Therefore, this study aims to investigate behavioral, electrocardiographic, and ventilatory characteristics of tambaquis exposed to anesthetic baths with etomidate. The study was conducted with juvenile tambaquis (27.38 ± 3.5g) n = 99, at etomidate concentrations of 2–4 mg.L -1, analyzing induction and anesthetic recovery behavior (experiment I), electrocardiogram (experiment II), and opercular movement (experiment III). Fish exposed to high concentrations of etomidate reached the stage of general anesthesia faster, however, the recovery time was longer, characterizing a dose-dependent relationship. Cardiorespiratory analyzes demonstrated a reduction in heart rate (69.19%) and respiratory rate (40.70%) depending on the concentration of etomidate used during anesthetic induction. During the recovery period, there was cardiorespiratory reversibility to normality. Therefore, etomidate proved to be safe as an anesthetic agent for this species at concentrations of 2 to 3 mg.L -1 for short-term anesthesia, but at higher doses the animals showed slow reversibility of anesthesia in a gradual manner and without excitability. The hemodynamic effect due to the rapid decrease in heart rate includes a negative factor of using higher concentrations of etomidate for Colossome macropomum anesthesia. [ABSTRACT FROM AUTHOR]

The development and application of functional feed ingredients represents a great opportunity to advance fish growth and health, boost the immune system, and induce physiological benefits beyond those provided by traditional feeds. In the present study, we looked at the feasibility of in vitro methods for screening the qualities of functional feed ingredients using the fish cell line RTgill-W1, which has never been used in fish nutrition, and the culture of Paramoeba perurans. Five functional feed ingredients (arginine, β-glucan, vitamin C, and two phytogenic feed additives) were selected to investigate their effects on cell viability and reactive oxygen species production. Three of the selected ingredients (arginine and two phytogenic feed additives) were additionally tested to assess their potential amoebicidal activity. As these functional ingredients are the core of a commercially available feed (Protec Gill, Skretting AS), their beneficial effects were further assessed in a field trial in fish affected by complex gill disease. Here, the analyzed parameters included the evaluation of macroscopic and histopathological gill conditions, pathogen detections, and analyses of plasma parameters. RTgill-W1 cell line assays were a good tool for screening functional ingredients and provided information about the optimal ingredient concentration ranges, which can be helpful for adjusting the concentrations in future feed diets. Through the culture of P. perurans, the tested ingredients showed a clear amoebicidal activity, suggesting that their inclusions in dietary supplements could be a viable way to prevent microbial infections. A three-week period of feeding Protec Gill slowed the disease progression, by reducing the pathogen load and significantly improving gill tissue conditions, as revealed by histological evaluation. The use of diets containing selected functional ingredients may be a feasible strategy for preventing or mitigating the increasingly common gill diseases, particularly in cases of complex gill disease, as documented in this study. [ABSTRACT FROM AUTHOR]

Nile tilapia (Oreochromis niloticus) is valued in aquaculture because of its quick development and ability to thrive in various environments. Myxosporeans are among the fish parasites that affect fish productivity, as they impact fish growth and reproduction, resulting in large fish deaths in farms and hatcheries. This study has been focused on morpho-molecular identification for the myxosporean parasites infecting Nile tilapia from three governorates in Egypt and assessment of gene expression of different cytokines (Interleukin-1βeta (IL-1β), major histocompatibility complex class II (MHC-II), and clusters of differentiation 4 (CD-4) and 8 (CD-8)) in tissues. Additionally, this work aimed to correlate the developed histopathological alterations and inflammatory reactions in gills with immunohistochemical expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-α). Finally, the infected fish's cortisol levels and blood glucose were assessed. Results of BLAST sequence analysis of the 18S rRNA for the collected protozoans confirmed Myxobolus agolus, M. brachysporus, M. tilapiae, and Henneguya species. The molecular characterization of the immunological status of gills revealed marked upregulation of different inflammatory cytokines in the gills of infected fish. There was a significantly increased serum cortisol and glucose level in infected fish compared with control, non-infected ones. Severe histopathological alterations were observed in the infected fish gills, associated with increased expression of iNOS and TNF-α and related to myxosporean infection. The present study provides new insights into oxidative stress biomarkers in Nile tilapia infected with Myxosporeans and elucidates the gill's immune status changes as a portal of entry for protozoa that contribute to tissue damage. [ABSTRACT FROM AUTHOR]

In real-world situations, marine fish farms accommodate multiple fish species and cohorts within the farm, leading to diverse farm layouts influenced by cage dimensions, configurations, and intricate arrangements. These cage management practices are essential to meet production demands, however, farm-level complexities can impact model predictions of waste deposition and benthic impact near fish cages. This is of particular importance when the cages are used for integrated multi-trophic aquaculture (IMTA) with benthic feeders, where this waste not only affects environmental conditions but also provides a potential food source. The Cage Aquaculture Particulate Output and Transport (CAPOT) model incorporated multiple species, cohorts, and cage arrangements to estimate waste distribution from a commercial fish farm in the Mediterranean between October 2018 and July 2019. This spreadsheet model estimated dispersion for individual fish cages using a grid resolution of 5 m x 5 m. The study categorized discrete production periods for each fish cage every month, aligning with intermittent changes in biomass and food inputs due to different cage management practices throughout production. This approach facilitated the use of detailed input data and enhanced model representativeness by considering variations in cage biomass, food types, settling velocities, and configurations. Model outputs, represented in contour plots, indicated higher deposition directly below fish cages that varied monthly throughout fish production cycles. Deposition footprints reflected changes in cage biomass, food inputs, and farm-level practices reflecting this real-world scenario where aquaculture does not follow a production continuum. Moreover, cohort dynamics and cage movements associated with the cage management practices of the fish farm influenced the quantity and fate of wastes distributed around fish cages, revealing variability in deposition footprints. Clearly, these findings have important implications for the design of benthic IMTA systems, with species such as sea cucumber and polychaetes. Variability in waste deposition creates challenges in identifying where the benthic organisms should be placed to allow optimal uptake of waste to meet their food requirements and increase survivability. Evidently, models have an important role to play and this study emphasizes the need for representative input data to describe actual food inputs, cage biomass changes, and management practices for more representative farm-scale modelling and essentially to improve particulate waste management. To effectively mitigate benthic impacts through IMTA, models must quantify and resolve particulate waste distribution and impact around fish farms to maintain a balanced system with net removal of wastes. Resolving farm-level complexities provides vital information about the variability of food availability and quality for extractive organisms that helps improve recycling of organic wastes in integrated systems, demanding a more representative modelling approach. [ABSTRACT FROM AUTHOR]

Duoculture has been reported to increase growth rates of some fishes when reared in combination, due to "shading" effects between the species. Two experiments, one involving outdoor cage-rearing in a reservoir, and the other, indoor tank-rearing, were conducted within each of three temperatures ranges (means of ~18.0°C, ~22.0°C and ~26.5°C), to determine whether duoculture of bluegill (BG) Lepomis macrochirus and yellow perch (YP) Perca flavescens would lead to improved growth relative to when the two species were reared separately. Juvenile bluegill and yellow perch were reared in triplicated groups each involving monoculture sets of 100% BG and 100% YP, and a duoculture set of 50% BG + 50% YP. Experiments in cages (Exp. 1) ran for 150 days while those in tanks ran for 126 days (Exp. 2). In Experiment 1, bluegill exhibited significantly greater (P<0.05) mean weight (P<0.05) in duoculture than in monoculture, under the high summer-like range of temperature (~26.5°C) over most of the experiment, whereas yellow perch showed no significant difference in mean weight in duoculture versus monoculture. By the end of a 150-d experiment, bluegill in duoculture outweighed those in monoculture by 62.5%. In Experiment 2, yellow perch in duoculture grew significantly larger than in monoculture (P<0.05) under the warm thermal regime (mean of ~22°C), while no significant differences were detected in mean weight of bluegill in monoculture versus duoculture. Yellow perch in duoculture outweighed those in monoculture by 33.1% at the end of the experiment. Yellow perch performed better in duoculture than in monoculture under the low thermal regime (mean of ~18°C) in both experiments. A significantly greater reduction of CVwt was observed for both bluegill and yellow perch in duoculture than in monoculture in Experiment 1, while no differences in CVwt reduction were detected for bluegill in Experiment 2. Feed conversion ratios (FCR) of bluegill and yellow perch reared in duoculture were significantly lower than for both fishes reared in monoculture in Experiment 1, while there were no significant differences in FCR among the three groups throughout most of Experiment 2. Findings indicate that duoculture of yellow perch and bluegill holds good potential to improve growth and FCR, and to reduce size variation by diminishing social interaction costs. [ABSTRACT FROM AUTHOR]

Clarias batrachus is a commercially important food fish. In the present study, effect of varying dietary protein levels was evaluated on the survival, growth parameters and proximate composition of C. batrachus. Diets comprising 25%, 30%, 35%, 40%, 45%, and 50% crude protein (CP) were supplied to fish in T1, T2, T3, T4, T5, and T6, respectively, at the rate of 5% of fish body weight for the entire 90 days, twice daily. Size of each stocked C. batrachus was recorded after 15 days. Results revealed 100% survival rate of C. batrachus in all treatments. Significantly highest (P<0.001) mean value of weight gain (g/fish), percent weight gain, daily growth rate, specific growth rate and protein efficiency ratio (PER) in C. batrachus were recorded, reared in T4 by feeding 40% CP in diet. The best FCR value (1.90±0.02) for C. batrachus was obtained in T4 by feeding 40%CP in diet. Mean value of water, ash, fat and protein contents (wet mass) were ranged 74.10–79.23%, 3.12–4.68%, 3.90–4.43% and 13.09–16.79% for C. batrachus in the studied treatment groups. Water content (%) was found significantly (P<0.05) higher in the body of C. batrachus for T1, T2, T3 and T6 than for T4 and T5. Ash was found significantly (P<0.05) higher in the fish reared in T4 and T5. Fat content in the wet body mass of C. batrachus was found significantly higher in T4 and T1. While, significant higher (P<0.05) values of mean protein content was noted in C. batrachus reared in T4 and T5. Body composition of C. batrachus was also categorically affected by body size, however, condition factor showed non-significant correlation in most of the relationships in the present study. Overall, results indicated that feeding appropriate diet (containing 40% CP) to the fish resulted good growth performance, lower FCR and higher protein content in the fish. Present study provides valuable knowledge of optimal dietary protein level in C. batrachus which will help in commercial success of aquaculture. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the influence of zeolite usage and stocking densities on various parameters, including ammonia removal from water, accumulation of heavy metals in fish organs, water quality, growth performance, feed efficiency, muscle composition, as well as hematological and biochemical parameters in European seabass (Dicentrarchus labrax) over a 90-day duration. A total of 2400 D. labrax with an initial weight of 9.83 ± 2.02 g and initial length of 9.37 ± 0.32 cm were distributed among 24 tanks. The research involved six distinct treatment groups, with two different zeolite levels (0 and 15 ppt) and three stocking density levels (50, 100, and 150 fish/m3), each replicated four times. The results of the research demonstrate a statistically significant improvement (p < 0.05) in water quality measures with the introduction of zeolite. The successful implementation of this amendment mitigated the adverse effects of fish density on water quality parameters. Higher stocking density negatively impacted European sea bass growth, feed utilization, and hemato-biochemical indicators. Zeolite use effectively alleviated these adverse effects, particularly on performance, feed utilization, hematological, and biochemical parameters. The study's results indicate that the utilization of zeolite has shown to be efficacious in mitigating the accumulation of heavy metals in both water and fish organs, while concurrently augmenting fish attributes. However, the increase in density led to a significant decrease in the accumulation of heavy metals in both water and fish organs. The present study highlights the capacity of natural zeolites to mitigate the negative consequences associated with water quality concerns. The efficiency of these zeolites in limiting the accessibility of heavy metals in polluted water is shown, hence minimizing their accumulation in fish organs. In addition, the improvement of fish performance has the capacity to have a beneficial influence on both the well-being and efficiency of fish in aquaculture. Additional research is essential to fully understand the complex molecular pathways involved in utilizing natural zeolite under different fish densities. [ABSTRACT FROM AUTHOR]

Aeromonas hydrophila is one of the major pathogenic bacteria responsible for causing severe outbreaks at fish farms and is also a major global public health concern. This bacterium harbors many virulence genes. The current study was designed to evaluate the antidrug and virulence potential of A. hydrophila by amplifying its antimicrobial resistance and virulence genes using PCR and examining their effects on fish tissues and organs. A total of 960 fish samples of Channa marulius and Sperata sarwari were collected from four sites of the rivers of the Punjab, Pakistan. A. hydrophila isolates were subjected to biochemical identification and detection of virulence and antimicrobial resistance (AMR) genes by PCR. We retrieved 181 (6.46%) A. hydrophila isolates from C. marulius and 177 (6.25%) isolates from S. sarwari. Amplification through PCR revealed the incidence of virulence genes in 95.7% of isolates in C. marulius and 94.4% in S. sarwari. Similarly, amplification through PCR also revealed occurrence of AMR genes in 87.1% of isolates in C. marulius and 83.9% in S. sarwari. Histopathological examination revealed congestion (5.2%) and hepatocyte necrosis (4.6%) in liver, lamellar fusion (3.3%) and the presence of bacterial colonies (3.7%) in gills, fin erosion (6%), and the presence of biofilms (3.5%) in tail fins of infected fish. Phylogenetic tree analysis of 16S rRNA and gyrB gene of A. hydrophila revealed 100% and 97% similarity, respectively, with 16S rRNA gene and gyrB of A. hydrophila isolated in previous studies. The results of antimicrobial susceptibility testing showed that all isolates demonstrated resistance to sulfamethoxazole, ampicillin, neomycin, and norfloxacin, while susceptibility to gentamicin, chloramphenicol, and tetracycline, and intermediate resistance was observed against cefotaxime. The results concluded that examined fish samples were markedly contaminated with virulent and multidrug strains of A. hydrophila which may be of a potential health risk. The study emphasizes the responsible antimicrobial use in aquaculture and the urgent need for effective strategies to control the spread of virulence and antimicrobial resistance genes in A. hydrophila. [ABSTRACT FROM AUTHOR]

Environmental pollution and overfishing of wild fish resources have led to a significant decrease in snakehead fish, thus leading to the increased demand for breeding the snakehead fish. Guangdong and Deqing snakehead fish are two common consumed varieties. However, their nutritional value was unclear. Therefore, this study aimed to evaluate the nutritional value of snakehead fish from Guangdong and Deqing varieties feeding with different fodders by analyzing and comparing the proximate composition, fatty acids and amino acids. Results showed that the contents of carbohydrate, energy and fat contents in Guangdong variety were lower than that in Deqing variety feeding commercial fodder or offal. Besides, Guangdong variety contained the highest contents of polyunsaturated fatty acids (27.99 ± 1.99%) and EPA + DHA (2.70 ± 0.04%), as well as total essential amino acid content (2550.29), compared to Deqing variety feeding commercial fodder or offal. Overall, snakehead fish from Guangdong variety displayed the highest nutritional value, and thus was a reasonable choice for farmers and consumers. The findings of this study would help farmers to choose the suitable feeding variety and patterns of snakehead fish from the perspective of fish nutritional value, which is beneficial to the sustainable fish farming. [ABSTRACT FROM AUTHOR]

Aeromonas spp. are the opportunistic pathogens that infect both aquatic and terrestrial homeotherms. They were commonly present in aquatic environments, including effluent, tap water, marine, river, and lake, where they are often isolated from aquatic animals, including fish, molluscs, and crustaceans. The Aeromonas infections can cause sepsis, ulcer, and other symptoms, resulting in the death of massive aquatic animals. Therefore, the prevention and control of Aeromonas is of great significance for the healthy development of aquaculture. In this study, we used modern molecular methods to enhance disease control of Aeromonas isolates from freshwater fish in Hebei Province. A total of 130 Aeromonas spp. isolates were isolated from freshwater fish farms in Hengshui, Handan, and Shijiazhuang and all 130 Aeromonas spp. isolates were sequenced for species identification. Of the 130 Aeromonas spp. isolates, 104 isolates were successfully sequenced, and BLAST analysis showed that Aeromonas veronii was predominant in freshwater fish farms in Hebei Province. In addition, 26 antibiotic resistance profiles were obtained from 102 fully cultured isolates among the 104 Aeromonas spp. isolates whose species was primarily identified, and 44 multidrug-resistant bacteria among the 102 isolates were identified using an antibiotic susceptibility test. Using the Multilocus Sequence Typing (MLST) method, 33 out of 44 multidrug-resistant isolates with 14 non-Aeromonas reference strains were selected for phylogenetic and MLST analysis, and all 33 multidrug-resistant isolates were A. veronii. A total of 30 new Sequence Types (STs) were obtained by comparing concatenated sequences (gyrB-groL-gltA-metG-ppsA-recA) on PubMLST website. Furthermore, recombination event analysis detected using RDP5 and ClonalFrameML software 42 and 49 recombination events, respectively, and 22 recombination events were validated by four or more algorithms. Since mutation and recombination events increase clonal diversity and single housekeeping gene sequence alignments are limited for identifying species, we propose the use of multiple concatenated sequence loci to increase discriminatory power. In addition, we propose that the MLST method is an appropriate technique to study and develop the resistance mechanisms of multidrug-resistant Aeromonas and to identify Aeromonas systematically in complex samples obtained from the environment. [ABSTRACT FROM AUTHOR]

Over the past two decades, increasing numbers of humpback whales have been returning to feed in the inshore waters of British Columbia (BC) where marine aquaculture farms are situated. This has led to growing concerns that the presence of aquaculture farms may pose an entanglement threat to humpback whales. However, it is not known whether aquaculture facilities attract humpback whales, or whether there are factors that increase the likelihood of humpback whale, becoming entangled and dying. We examined eight reports of humpback whales interacting with Atlantic salmon farms in BC from 2008 to 2021 to evaluate the conditions that may have contributed to their entanglements. Of the eight entangled humpbacks, three individuals died and five were successfully disentangled and released. All were young animals (1 calf, 7 subadults). Multiple factors were associated with two or more of the reported incidents. These included facility design, environmental features, seasonality, humpback whale age, and feeding behaviour. We found that humpback whales were most commonly entrapped in the predator nets of the aquaculture facilities (6/8 incidents), and were less often entangled in anchor support lines (2/8). The presence of salmon smolts did not appear to be an attractant for humpback whales given that half of the reported entanglements (4/8) occurred at fallowed salmon farms. Almost all of the entanglements (7/8) occurred in late winter (prior to the seasonal return of humpbacks) and during late fall (after most humpbacks have migrated south). Overall, the number of humpback whales impacted by fish farms was small compared to the numbers that return to BC (> 7,000) and accounted for <6% of all types of reported entanglements in BC. Human intervention was required to release humpback whales at fish farms, which points to the need to have well-established protocols to minimize entanglements and maximize successful releases. [ABSTRACT FROM AUTHOR]

Rice fish co-culture synergistically boosts food production, resulting in numerous advantages across the environmental, social, and financial domains. A study was conducted to investigate the effects of three different rice spacing densities, rice high density (RHD) 9inch×12inch, rice medium density (RMD) 12inch × 12inch, rice low density (RLD) 15inch×12inchon both rice and fish. Various parameters were assessed to evaluate the performance of the co-culture system, including water quality, growth parameters, muscle quality, soil characteristics, rice stem characteristics, and rice yield parameters. When comparing the species, it was observed that GMT (Genetically Male Tilapia) demonstrated superior weight gain (303.13g vs 296.41g) and specific growth rate (1.16 vs 1.15). Regarding the proximate composition, results showed that RMD had the highest crude protein and fat content compared to RLD and RHD. GMT also exhibited greater crude protein and fat content than Cyprinus carpio, with RMD showing the highest values. Treatment groups significantly influenced the amino acid profile of experimental species, with RMD exhibiting the highest values. GMT showed significantly higher levels of essential, non-essential, half-essential, and umami amino acids compared to Cyprinus carpio. The interaction between RMD and GMT further demonstrated significant differences in various amino acid categories with RMD. A non-significant difference was observed among the treatments regarding soil biochemical characteristics. Regarding the rice stem characters, the height of the plant, panicle length, and stem length of rice were found to be comparable in the RMD and RLD groups however, significantly higher in RHD. Regarding rice yield parameters, no significant differences were observed among the other treatment groups, except for yield per hectare (yield/ha), which was significantly higher in the RHD group compared to RMD and RLD. Additionally, 1000-grain weight and panicle number (ears per hill) were significantly higher in the RLD treatment than in the other treatments. In conclusion, our findings indicate that the RMD treatment consistently yielded superior results compared to RLD and RHD. Furthermore, within the rice-fish co-culture system, GMT proved to be a more competent species compared to Cyprinus carpio. The study provides data to understand the interactions between rice spacing density, fish growth and overall productivity can guide the development of sustainable and profitable rice-fish co-culture systems. [ABSTRACT FROM AUTHOR]

Described as the 'main ecological factor', temperature, strongly affects the physiological stress responses of fish. In order to evaluate the effects of temperature variations on fish culture and food value chain, the present study was designed as a climate change model. Furthermore, the present study provides a theoretical basis for a better understanding of the mechanisms of the environmentally induced changes. In this direction, we examined the blood physiology and oxidative stress responses induced by temperature variation in the rainbow trout, a temperature-sensitive cold-water fish. The obtained results showed that climate changes promoted the inhibited activities' expressions and the development of potential tissue and hematological defense mechanisms against temperature-induced toxic damage. This study showed that climate change could be a subset of the studies on the stress physiology in aquaculture, which can be developed for new experimental designs and research collaborations. Furthermore, it highlights knowledge gaps to guide future research in this emerging field. [ABSTRACT FROM AUTHOR]

Tilapia Lake Virus (TiLV) is a disease that affects tilapia fish, causing a high rate of sudden death at any stage in their life cycle. Unfortunately, there are currently no effective antiviral drugs or vaccines to prevent or control the progression of this disease. Researchers have discovered that the CRM1 protein plays a critical function in the development and spreading of animal viruses. By inhibiting CRM1, the virus's spread in commercial fish farms can be suppressed. With this in mind, this study intended to identify potential antiviral drugs from two different tropical mangrove plants from tropical regions: Heritiera fomes and Ceriops candolleana. To identify promising compounds that target the CRM1 protein, a computer-aided drug discovery approach is employed containing molecular docking, ADME (absorption, distribution, metabolism and excretion) analysis, toxicity assessment as well as molecular dynamics (MD) simulation. To estimate binding affinities of all phytochemicals, molecular docking is used and the top three candidate compounds with the highest docking scores were selected, which are CID107876 (-8.3 Kcal/mol), CID12795736 (-8.2 Kcal/mol), and CID12303662 (-7.9 Kcal/mol). We also evaluated the ADME and toxicity properties of these compounds. Finally, MD simulation was conducted to analyze the stability of the protein-ligand complex structures and confirm the suitability of these compounds. The computational study demonstrated that the phytochemicals found in H. fomes and C. candolleana could potentially serve as important inhibitors of TiLV, offering practical utility. However, further in vivo investigations are necessary to investigate and potentially confirm the effectiveness of these compounds as antiviral drugs against the virus TiLV. [ABSTRACT FROM AUTHOR]

The objective of this study was to reveal the growth, colouration and gonado-physiological changes due to the exogenous aromatase inhibitor (AIs) in an ornamental fish. 17α-methyltestosterone (MT) and letrozole (LET) were used as potential AIs. The AI were supplemented with a gel-based feed (LET: 50, 100, 150 and MT: 12.5, 25, 37.5 mg/kg feed) in Rosy barb, Pethia conchonius fry. The fishes were reared in a 45-L glass tank using AI treated gel-based feed for 3 months. Growth in AI-based diets was reduced but the reduction was minimal compared to the control. At 25 mg/kg feed of 17 MT, the highest male proportion (84.72% 6.05%) was recorded, which was significantly higher (P≤0.05) than other groups. L*, a*, and b* values showed that 17α-MT-fed groups had brighter coloration (P≤0.05). Histological sections showed that LET-17α-MT suppressed ovarian development, causing atretic oocytes. Testicular development was unaffected. 25 mg/kg-treated feed increased SOD, CAT, GST, and GPX. The AI (MT) at 25 mg/kg gel-based feed could therefore be utilised for musculinization without impacting growth, colour, and antioxidant activity of rosy barb, which serves the entire male population in the ornamental fish sector. [ABSTRACT FROM AUTHOR]

Background: In Brazilian Amazon, deforestation and other anthropogenic activities as a consequence of human occupation have created new and artificial larval habitats for anopheline mosquitoes, providing conditions for oviposition, development and expansion of malaria vector populations. Objectives: This study aimed to structurally characterize and describe the entomological and limnological parameters of Anopheles larval habitats from a malaria region in northern Brazilian Amazon. Methods: Fifty-two larval habitats were investigated in the District of Ilha de Santana, in the Brazilian state of Amapá, comprising fish farming tanks, ponds, and streams. For entomological parameters, the immature larvae were collected monthly from July 2019 to June 2020. For limnological parameters, the water samples were collected from 20 larval habitats during the sampling period. The data were analyzed using Generalized Linear Models, Multivariate analyses, and Kruskal-Wallis tests. Results: Fifty habitats were positive for Anopheles larvae and a total of nine species were collected. The fish farming tanks had the highest abundance of larvae compared with ponds and streams. Anopheles darlingi, Anopheles nuneztovari s.l. and Anopheles triannulatus were collected in 94% of the larval habitats and showed the highest positivity index. The degree of shade and the type of water of the breeding sites were important factors for the presence of the main malaria vector, A. darlingi. This species was the most affected by pH, total dissolved solids, electrical conductivity, and nitrate. Conclusions: Our findings indicate that fish farming tanks are major contributors to vector anopheline abundance and malaria transmission. Vector control strategies focused on these habitats are urgently needed. [ABSTRACT FROM AUTHOR]

Megalocytiviruses (MCVs) are double-stranded DNA viruses known to infect important freshwater and marine fish species in the aquaculture, food, and ornamental fish industries worldwide. Infectious spleen and kidney necrosis virus (ISKNV) is the type species within the genus Megalocytivirus that causes red seabream iridoviral disease (RSIVD) which is a reportable disease to the World Animal Health Organization (WOAH). To better control the transboundary spread of this virus and support WOAH reporting requirements, we developed and partially validated a TaqMan real-time qPCR assay (ISKNV104R) to detect all three genotypes of ISKNV, including the two genotypes that cause RSIVD. Parameters averaged across 48 experiments used a 10-fold dilution series of linearized plasmid DNA (107–101 copies), carrying a fragment of the three-spot gourami iridovirus (TSGIV) hypothetical protein revealed that the assay was linear over 7 orders of magnitude (107–101), a mean efficiency of 99.97 ± 2.92%, a mean correlation coefficient of 1.000 ± 0.001, and a limit of detection (analytical sensitivity) of ≤10 copies of TSGIV DNA. The diagnostic sensitivity and specificity for the ISKNV104R qPCR assay was evaluated and compared to other published assays using a panel of 397 samples from 21 source populations with different prevalence of ISKNV infection (0–100%). The diagnostic sensitivity and specificity for the ISKNV104R qPCR assay was 91.99% (87.28–95.6; 95% CI) and 89.8% (83.53–94.84). The latent class analysis showed that the ISKNV104R qPCR assay had similar diagnostic sensitivities and specificities with overlapping confidence limits compared to a second TaqMan qPCR assay and a SYBR green assay. This newly developed TaqMan assay represents a partially validated qPCR assay for the detection of the three genotypes of the species ISKNV. The ISKNV104R qPCR assay once fully validated, will serve as an improved diagnostic tool that can be used for ISKNV surveillance efforts and diagnosis in subclinical fish to prevent further spread of MCVs throughout the aquaculture and ornamental fish industries. [ABSTRACT FROM AUTHOR]

The study of nutraceuticals and their connection to immunity is an expanding field of research. The use of nutraceuticals to alleviate stress and enhance immunity in adverse aquaculture environments have been examined to a certain extent. To elucidate the understanding, we focused on the immunological effect of membrane-separated 13% anthocyanin standardized elderberry (EB) extract with maltodextrin excipient, widely used first-line nutraceuticals to augment the immunity, in aquaculture fish, Nile tilapia. To evaluate the potential of EB-extract, we assessed their capability to enhance lymphocyte proliferation and interleukin-2 production in an in-vitro condition using spleen and thymus lymphocytes. The experiments on spleen and thymus T-cells demonstrated significantly higher T-cell proliferation by EB-extract when lectin mitogen Con A was present as a stimulator. Likewise, our spleen B-cell proliferation result reveals a significant effect of EB-extracts, along with B-cell stimulator non-lectin mitogen LPS. Further, the quantification of IL-2 indicates elevated IL-2 levels when spleen T-cells were cultured with EB-extracts and with Con A present as a stimulator. These suggest that 13% anthocyanin standardized EB-extracts can aggrandize fish cells' cellular and humoral immune responses. With further research, elderberry extracts could be used to supplement commercial feed in aquaculture to reduce stress and stimulate the immune response. [ABSTRACT FROM AUTHOR]

The Asian giant has agitated foreign trade in Latin America due to easy access to this market, tariff policies, and international agreements. In the face of a globalized world, in the last decade fisheries and aquaculture entrepreneurs of Latin American countries have taken on the challenge of getting their products known at International Fisheries and Aquaculture Exhibition fairs in Asian countries, which has generated an increase in the exportation of their products. Fishing and aquaculture exports are a variable of the economy of each country reflected in the gross domestic product and foreign exchange results. The present research work analyzed the fishing and aquaculture sector through the first difference Generalized Method of Moments estimator to establish the behavior of exports from Latin American countries to Asia, the production of each Latin American country, and the subsequent effect on the economic growth of the fishing and aquaculture sector during the period 2012–2019. The findings of this article suggest the significant positive relationship between output and economic growth, and a non-significant negative relationship between exports to East Asia and the economy. [ABSTRACT FROM AUTHOR]

In this paper we present the design of an open-source and low-cost buoy prototype for remote monitoring of water quality variables in fish farming. The designed battery-powered system periodically measures temperature, pH and dissolved oxygen, transmitting the information locally through a low-power wide-area network protocol to a gateway connected to a cloud service for data storage and visualization. We provide a novel buoy design that can be easily constructed with off-the-shelf materials, delivering a stable anchored float for the IoT device and the probes immersed in the water pond. The prototype was tested at an operating fish farm, showing promising results for a low-cost remote monitoring tool that enables automatic data acquisition and storage in fish farming scenarios. All the elements of this design, including hardware and software designs, are freely available under permissive licenses as an open-source project. [ABSTRACT FROM AUTHOR]

Pacific salmon and trout populations are affected by timber harvest, the removal and alteration of riparian vegetation, and the resulting physical changes to water quality, temperature, and associated delivery of high-quality terrestrial prey. Juvenile salmon and trout growth, a key predictor of survival, is poorly understood in the context of current and future (climate-change mediated) conditions, with resource managers needing information on how land use will impact future river conditions for these commercially and culturally important species. We used the Heat Source water temperature modeling framework to develop a spatiotemporal model to assess how riparian canopy and vegetation preservation and addition could influence river temperatures under future climate predictions in a coastal river fed by a moraine-dammed lake: the Quinault River in Washington State. The model predicted higher water temperatures under future carbon emission projections, representative concentration pathway (RCP) 4.5 and 8.5, with varying magnitude based on different riparian vegetation scenarios. We used the daily average temperature output from these scenarios to predict potential juvenile fish growth using the Wisconsin bioenergetics model. A combination of riparian vegetation removal and continued high carbon emissions resulted in a predicted seven-day average daily maximum temperature (7DADM) increase of 1.7°C in the lower river by 2080; increases in riparian shading mitigate this 7DADM increase to only 0.9°C. Under the current thermal regime, bioenergetics modeling predicts juvenile fish lose weight in the lower river; this loss of potential growth worsens by an average of 20–83% in the lower river by 2080, increasing with the loss of riparian shading. This study assess the impact of riparian vegetation management on future thermal habitat for Pacific salmon and trout under warming climates and provide a useful spatially explicit modeling framework that managers can use to make decisions regarding riparian vegetation management and its mechanistic impact to water temperature and rearing juvenile fish. [ABSTRACT FROM AUTHOR]

With the intensification of fish farming, the amount of residues also increased. One of the by-products generated is leather. However, several factors influence its quality, among them, the types of tanning used. Paiche (Arapaima gigas) is the largest freshwater fish in the world, and therefore has great potential in the use of leather, in addition to being one of the most cultivated fish in the Rondônia state. The aimed was to evaluate the physicomechanical resistance, histological and morphological aspects in different directions of the fibers of the paiche to evaluate the tanning with chromium oxide and vegetable tannin. Paiches with an average weight of 12.0 kg were used, skins were made and tanned using chromium and vegetable tannin as techniques. After tanning, 20 specimens were removed in longitudinal, transverse and diagonal directions to the fish body, to determine resistance in dynamometer and leather for histological analysis, scanning electron microscopy and physical-chemical analysis. The average thickness of the specimens of the leathers ranged 1.79mm to 2.82mm, in addition, there was no interaction between the type of tanning agent and the directions obtained for strength, traction and elongation. Regarding the progressive tearing test, there was also no interaction effect. However, the defined factors had relevant differences for the maximum and average amount applied, and the leathers tanned with vegetable tannin expanded to larger dimensions 110.19 and 85.52 N. According to the images obtained by histology and scanning microscopy, they presented that in the longitudinal and transverse direction the collagen fibers are presented in layers parallel to the leather surface and in the diagonal direction the interlacing is more intense, that is, in addition to the overlapping layers intercalated thinner, close to the surface, fiber bundles can also be seen crossing each other. It is concluded that leathers tanned with vegetable tannin have less resistance than leathers tanned with chromium salts for traction to rupture and greater resistance to tear. [ABSTRACT FROM AUTHOR]

In this study, we determined the effects of dietary chitosan on the growth, biochemical composition, gut microbiota, and hematological and histological parameters of juvenile Barbonymus gonionotus. Three test diets containing three different concentrations (1, 2, and 3 g kg-1 feed) of dietary chitosan were formulated. A basal diet without dietary chitosan was considered a control, and the fish were reared for 60 days. Comparing the effects of the dietary chitosan-containing diets with those of the control diet, we found that dietary chitosan significantly improved the muscle growth, nutrient and mineral contents, hematological parameters, lactic acid bacterium abundance, and digestive enzyme activities of B. gonionotus. Moreover, dietary chitosan significantly inhibited the growth of pathogenic bacteria in fish. Interestingly, an increase in the dietary chitosan level significantly enhanced the protein contents of the muscles and inversely significantly decreased the lipid contents compared to those with the basal diet. Quantitative study revealed that dietary chitosan significantly enhanced the length of intestinal villi, and qualitative study showed that dietary chitosan considerably reduced the fat content in the liver and improved the morphology of the kidney compared to those with the basal diet. Taken together, our results suggest that the application of dietary chitosan at a dose of 1 g kg-1 feed produced the highest benefit to treated B. gonionotus, indicating its potential for safe use in aquaculture. [ABSTRACT FROM AUTHOR]

Humans are altering biological systems at unprecedented rates, and these alterations often have longer-term evolutionary impacts. Most obvious is the spread of resistance to pesticides and antibiotics. There are a wide variety of management strategies available to slow this evolution, and there are many reasons for using them. In this paper, we focus on the economic aspects of evolution management and ask: When is it economically beneficial for an individual decision-maker to invest in evolution management? We derive a simple dimensionless inequality showing that it is cost-effective to manage evolution when the percentage increase in the effective life span of the biological resource that management generates is larger than the percentage increase in annual profit that could be obtained by not managing evolution. We show how this inequality can be used to determine optimal investment choices for single decision-makers, to determine Nash equilibrium investment choices for multiple interacting decision-makers, and to examine how these equilibrium choices respond to regulatory interventions aimed at stimulating investment in evolution management. Our results are illustrated with examples involving Bacillus thuringiensis (Bt) crops and antibiotic use in fish farming. Humans are altering biological systems at unprecedented rates and these alterations often have longer-term evolutionary impacts, such as the spread of resistance to pesticides and antibiotics. In this study, a simple mathematical criterion is derived determining when it is economically beneficial to invest in strategies for controlling and managing evolutionary change. [ABSTRACT FROM AUTHOR]

Tenacibaculosis is a bacterial ulcerative disease affecting marine fish and represents a major threat to aquaculture worldwide. Its aetiological agents, bacteria belonging to the genus Tenacibaculum, have been present in Norway since at least the late 1980's and lead to regular ulcerative outbreaks and high mortalities in production of farmed salmonids. Studies have shown the presence of several Tenacibaculum species in Norway and a lack of clonality in outbreak-related strains, thus preventing the development of an effective vaccine. Hence, a thorough examination of the bacterial diversity in farmed fish presenting ulcers and the geographical distribution of the pathogens should provide important insights needed to strengthen preventive actions. In this study, we investigated the diversity of Tenacibaculum strains isolated in 28 outbreaks that occurred in Norwegian fish farms in the period 2017–2020. We found that 95% of the 66 strains isolated and characterized, using an existing MultiLocus Sequence Typing system, have not previously been identified, confirming the high diversity of this genus of bacteria in Norway. Several of these Tenacibaculum species seem to be present within restricted areas (e.g., Tenacibaculum dicentrarchi in western Norway), but phylogenetic analysis reveals that several of the strains responsible of ulcerative outbreaks were isolated from different localities (e.g., ST- 172 isolated from northern to southern parts of Norway) and/or from different hosts. Understanding their reservoirs and transmission pathways could help to address major challenges in connection with prophylactic measures and development of vaccines. [ABSTRACT FROM AUTHOR]

Monitoring variables such as dissolved oxygen, pH, and pond temperature is a key aspect of high-quality fish farming. Machine learning (ML) techniques have been proposed to model the dynamics of such variables to improve the fish farmer's decision-making. Most of the research on ML in aquaculture has focused on scenarios where devices for real-time data acquisition, storage, and remote monitoring are available, making it easy to develop accurate ML techniques. However, fish farmers do not necessarily have access to such devices. Many of them prefer to use equipment to manually measure these variables limiting the amount of available data to process. In this work, we study the use of random forests, multivariate linear regression, and artificial neural networks in scenarios with limited amount of measurements to analyze data from water-quality variables that are commonly measured in fish farming. We propose a methodology to build models in two scenarios: i) estimation of unobserved variables based on the observed ones, and ii) forecasting when a low amount of data is available for training. We show that random forests can be used to forecast dissolved oxygen, pond temperature, pH, ammonia, and ammonium when the water pond variables are measured only twice per day. Moreover, we showed that these prediction models can be implemented on a mobile-based information system and run in an average smartphone that fish farmers can afford. [ABSTRACT FROM AUTHOR]

A Bayesian Belief Network, validated using past observational data, is applied to conceptualize the ecological response of Lake Maninjau, a tropical lake ecosystem in Indonesia, to tilapia cage farms operating on the lake and to quantify its impacts to assist decision making. The model captures ecosystem services trade-offs between cage farming and native fish loss. It is used to appraise options for lake management related to the minimization of the impacts of the cage farms. The constructed model overcomes difficulties with limited data availability to illustrate the complex physical and biogeochemical interactions contributing to triggering mass fish kills due to upwelling and the loss in the production of native fish related to the operation of cage farming. The model highlights existing information gaps in the research related to the management of the farms in the study area, which is applicable to other tropical lakes in general. Model results suggest that internal phosphorous loading (IPL) should be recognized as one of the primary targets of the deep eutrophic tropical lake restoration efforts. Theoretical and practical contributions of the model and model expansions are discussed. Short- and longer-term actions to contribute to a more sustainable management are recommended and include epilimnion aeration and sediment capping. [ABSTRACT FROM AUTHOR]

Vale do Rio Juruá in western Acre, Brazil, is a persistent malaria transmission hotspot partly due to fish farming development that was encouraged to improve local standards of living. Fish ponds can be productive breeding sites for Amazonian malaria vector species, including Nyssorhynchus darlingi, which, combined with high human density and mobility, add to the local malaria burden.This study reports entomological profile of immature and adult Ny. darlingi at three sites in Mâncio Lima, Acre, during the rainy and dry season (February to September, 2017). From 63 fishponds, 10,859 larvae were collected, including 5,512 first-instar Anophelinae larvae and 4,927 second, third and fourth-instars, of which 8.5% (n = 420) were Ny. darlingi. This species was most abundant in not-abandoned fishponds and in the presence of emerging aquatic vegetation. Seasonal analysis of immatures in urban landscapes found no significant difference in the numbers of Ny. darlingi, corresponding to equivalent population density during the rainy to dry transition period. However, in the rural landscape, significantly higher numbers of Ny. darlingi larvae were collected in August (IRR = 5.80, p = 0.037) and September (IRR = 6.62, p = 0.023) (dry season), compared to February (rainy season), suggesting important role of fishponds for vector population maintenance during the seasonal transition in this landscape type. Adult sampling detected mainly Ny. darlingi (~93%), with similar outdoor feeding behavior, but different abundance according to landscape profile: urban site 1 showed higher peaks of human biting rate in May (46 bites/person/hour), than February (4) and September (15), while rural site 3 shows similar HBR during the same sampling period (22, 24 and 21, respectively). This study contributes to a better understanding of the larvae biology of the main malaria vector in the Vale do Rio Juruá region and, ultimately will support vector control efforts. [ABSTRACT FROM AUTHOR]

Rearing habitat for juvenile Chinook Salmon (Oncorhynchus tshawytscha) in California, the southernmost portion of their range, has drastically declined throughout the past century. Recently, through cooperative agreements with diverse stakeholders, winter-flooded agricultural rice fields in California's Central Valley have emerged as ecologically functioning floodplain rearing habitat for juvenile Chinook Salmon. From 2013 to 2016, we conducted a series of experiments examining methods to enhance habitat benefits for fall-run Chinook Salmon reared on winter-flooded rice fields in the Yolo Bypass, a modified floodplain managed for flood control, agriculture, and wildlife habitat in the Sacramento River Valley of California. Investigations included studying the effect of 1) post-harvest field substrate; 2) depth refugia; 3) duration of field drainage; and 4) duration of rearing occupancy on in-situ diet, growth and survival of juvenile salmon. Post-harvest substrate treatment had only a small effect on the lower trophic food web and an insignificant effect on growth rates or survival of rearing hatchery-origin, fall-run Chinook Salmon. Similarly, depth refugia, created by trenches dug to various depths, also had an insignificant effect on survival. Rapid field drainage yielded significantly higher survival compared to drainage methods drawn out over longer periods. A mortality of approximately one third was observed in the first week after fish were released in the floodplain. This initial mortality event was followed by high, stable survival rates for the remainder of the 6-week duration of floodplain rearing study. Across years, in-field survival ranged 7.4–61.6% and increased over the course of the experiments. Despite coinciding with the most extreme drought in California's recorded history, which elevated water temperatures and reduced the regional extent of adjacent flooded habitats which concentrated avian predators, the adaptive research framework enabled incremental improvements in design to increase survival. Zooplankton (fish food) in the winter-flooded rice fields were 53-150x more abundant than those sampled concurrently in the adjacent Sacramento River channel. Correspondingly, observed somatic growth rates of juvenile hatchery-sourced fall-run Chinook Salmon stocked in rice fields were two to five times greater than concurrently and previously observed growth rates in the adjacent Sacramento River. The abundance of food resources and exceptionally high growth rates observed during these experiments illustrate the potential benefits of using existing agricultural infrastructure to approximate the floodplain wetland physical conditions and hydrologic patterns (shallow, long-duration inundation of cool floodplain habitats in mid-winter) under which Chinook Salmon evolved and to which they are adapted. [ABSTRACT FROM AUTHOR]

The health and environmental risks associated with antibiotic use in aquaculture have promoted bacterial probiotics as an alternative approach to control fish infections in vulnerable larval and juvenile stages. However, evidence-based identification of probiotics is often hindered by the complexity of bacteria-host interactions and host variability in microbiologically uncontrolled conditions. While these difficulties can be partially resolved using gnotobiotic models harboring no or reduced microbiota, most host-microbe interaction studies are carried out in animal models with little relevance for fish farming. Here we studied host-microbiota-pathogen interactions in a germ-free and gnotobiotic model of rainbow trout (Oncorhynchus mykiss), one of the most widely cultured salmonids. We demonstrated that germ-free larvae raised in sterile conditions displayed no significant difference in growth after 35 days compared to conventionally-raised larvae, but were extremely sensitive to infection by Flavobacterium columnare, a common freshwater fish pathogen causing major economic losses worldwide. Furthermore, re-conventionalization with 11 culturable species from the conventional trout microbiota conferred resistance to F. columnare infection. Using mono-re-conventionalized germ-free trout, we identified that this protection is determined by a commensal Flavobacterium strain displaying antibacterial activity against F. columnare. Finally, we demonstrated that use of gnotobiotic trout is a suitable approach for the identification of both endogenous and exogenous probiotic bacterial strains protecting teleostean hosts against F. columnare. This study therefore establishes an ecologically-relevant gnotobiotic model for the study of host-pathogen interactions and colonization resistance in farmed fish. Author summary: The protection provided by host commensal microbiota against pathogens is a long-known phenomenon fostering the notion that introducing beneficial bacteria could reduce or prevent infections. However, the identification of such protective microorganisms is hampered by the poor reproducibility and relevance of current in vivo models. We developed procedures to raise germ-free rainbow trout larvae to study the determinants of microbiota-associated resistance to infection. We showed that the fish pathogen Flavobacterium columnare rapidly kills infected germ-free but not conventional larvae. We then re-colonized germ-free larvae with bacteria originating from cultured fish microbiota and identified two bacterial species providing full protection against infection. Our approach constitutes a rational and potentially high throughput in vivo strategy to study host-pathogen interactions and resistance to infection in fish. The identification of probiotic bacteria protecting rainbow trout and potentially other fish against F. columnare could also contribute to improve aquaculture sustainability and health. [ABSTRACT FROM AUTHOR]

Nile tilapia, Oreochromis niloticus is the third most commonly farmed finfish species in the world, accounting for nearly 5% of global aquaculture production. In the past few decades much of the success of this species has been attributed to the development and distribution of Genetically Improved Farmed Tilapia (GIFT). Despite the increasing availability of GIFT, the productivity of small-scale farming remains highly variable, particularly in developing nations. Commercial fish-feed pellets can increase fish farm productivity; however, many small-scale farmers rely on other means of feeding fish due to the high cost and limited availability of commercial fish feed pellets. Therefore, understanding how locally-sourced feeds affect the production of GIFT is an important step towards improving feeding practices, particularly for farmers with low financial capital. This study used stable isotope analysis (SIA) and 16S rRNA gene sequencing to compare the effects of a locally-sourced vegetable-based diet and commercial pellet-based diets on the relative condition, nutrient assimilation patterns and gastrointestinal microbiota of GIFT. GIFT fed a locally-sourced diet were smaller, and in a significantly poorer condition than those fed with commercial fish feeds. SIA showed no differences in dietary carbon between the two diets; however, δ13C, poor fish condition and the abundance of specific bacterial taxa (of such as Fusobacteria) were correlated. SIA revealed that GIFT fed locally-sourced diets that predominantly consisted of vegetables were significantly enriched in δ15N despite a perceived lack of dietary protein. This enrichment suggests that GIFT fed a locally-sourced diet may be supplementing their diet via cannibalism, a behaviour representative of poor farming practice. Overall this study highlights the need to increase the availability of suitable GIFT feeds in developing nations. The development a low-cost feed alternative could improve the success of small-scale GIFT farmers in PNG, increasing both food and income security within the region. [ABSTRACT FROM AUTHOR]

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), exhibit antibacterial and anti-inflammatory activities. Furthermore, diets rich in n-3 PUFAs are known to improve disease resistance and limit pathogen infection in commercial aquaculture fishes. In this study, we examined the effects of transgenic overexpression of n-3 PUFA biosynthesis genes on the physiological response to bacterial infection in tilapia. We first established tilapia strains with single or dual expression of salmon delta-5 desaturase and/or delta-6 desaturase and then challenged the fish with Vibrio vulnificus infection. Interestingly, our data suggest that n-3 PUFA-mediated alterations in gut microbiota may be important in determining disease outcome via effects on immune response of the host. Both liver- and muscle-specific single and dual expression of delta-5 desaturase and delta-6 desaturase resulted in higher n-3 PUFA content in transgenic fish fed with a LO basal diet. The enrichment of n-3 PUFAs in dual-transgenic fish is likely responsible for their improved survival rate and comparatively reduced expression of inflammation- and immune-associated genes after V. vulnificus infection. Gut microbiome analysis further revealed that dual-transgenic tilapia had high gut microbiota diversity, with low levels of inflammation-associated microbiota (i.e., Prevotellaceae). Thus, our findings indicate that dual expression of transgenic delta-5 and delta-6 desaturase in tilapia enhances disease resistance, an effect that is associated with increased levels of n-3 PUFAs and altered gut microbiota composition. [ABSTRACT FROM AUTHOR]

The relative importance of bottom-up versus top-down effects in aquatic ecosystems remains a longstanding and ongoing controversy. To investigate these effects on phytoplankton communities in freshwater lakes, phytoplankton and zooplankton were sampled, and physical-chemical variables were measured during spring and summer in two important freshwater lakes in northern China: Nansi Lake and Dongping Lake. The redundancy analysis results showed that phytoplankton density and biomass were regulated by physical-chemical variables (bottom-up effects) and predation (top-down effects) together, and the former was more prominent in both lakes. However, the correlation analysis indicated that the top-down effects of zooplankton on phytoplankton were not significant in spring and summer in both lakes, while the bottom-up regulation of physical-chemical variables on phytoplankton had different patterns in the two lakes. In Nansi Lake, the bottom-up effects of physical-chemical variables on phytoplankton were weaker in summer than that in spring due to the abundant nutrients in summer. In Dongping Lake, the bottom-up effects of physical-chemical on phytoplankton were significant both in spring and summer, and the dominant bottom-up control factor shifted from total nitrogen in spring to total phosphorus in summer, with an increased ratio of nitrogen to phosphorus due to changes in limiting factors. In the two studied lakes, with fish culture, the bottom-up effects of phytoplankton on zooplankton were more important than the top-down effects of zooplankton on phytoplankton. These results demonstrate the interactions between phytoplankton and zooplankton and highlight the importance of phytoplankton regulation in freshwater lakes, which has implications for the effective management of freshwater lake ecosystems. [ABSTRACT FROM AUTHOR]

Most Atlantic salmon mariculture operations use open sea cages for the grow out phase. The ultimate fate and effects of the effluents and the possibilities of disease transfer between fish farms are major concerns for farmers, governance and the general public alike. Numerical model systems applied to studying and managing effluents and disease transfer in mariculture must realistically resolve the hydrodynamics in the vicinity of the fish farms. In the present study, the effects of the aquaculture structures on the current patterns were introduced in the ocean model system SINMOD. The drag parameters for the ocean model were determined by comparing the simulation results from the ANSYS Fluent ® software suite and SINMOD in an idealized channel setting with uniform currents. The model was run for a number of realistic scenarios in high horizontal resolution (∼30 m) with sea cages influencing the flow field. Comparisons between extensive current measurements and the simulation results showed that the model system reproduced the current local current field well. By running simulation scenarios with and without the effects of the sea cages on the flow field, it was possible to assess the importance of such effects for numerical dispersal models and aquaculture environment interactions simulations and hence for assessment of environmental impacts. [ABSTRACT FROM AUTHOR]

Piscivorous avian species are the main source of catfish depredation at aquaculture facilities in Mississippi, resulting in the economic loss of millions of dollars every year. Most notable of these avian species are the double-crested cormorant (Phalacrocorax auritus), great blue heron (Ardea herodias), and great egret (A. alba). Understanding why these species select specific ponds can increase management efficiency directed at avian dispersal and provide insight into their decision making with respect to foraging behavior. We collected species presence data on catfish ponds by flying 35 surveys from October through April of 2015–2017, during which an average of 973 catfish ponds were observed each year. We collected data associated with each pond's physical surroundings and contents and used occupancy modeling to determine their influence on avian occupancy probability. We also collected data associated with stocking practices and catfish health on a subset of ponds, and constructed resource selection functions to model their influence on avian presence. Pond area was positively related to occupancy probability of each species. Cormorant occupancy increased as pond distance from forest cover and activity centers, such as workshops and offices, increased. Distance to nearest activity center was positively related to egret occupancy, while distance to nearest forested area was negative. Ponds containing diseased catfish had an increased probability of use by both herons and egrets. In general, cormorants and egrets showed greater probability of use on the periphery of pond clusters. The abundance of catfish was positively related to cormorant and heron presence. Specific pond contents and characteristics influenced presence of each avian species in different ways, including fish species cultured, production methods, pond systems, and fish types. Many pond selection relationships were species-specific, illustrating inherent differences in their foraging ecology. Consequently, specific management actions aimed to reduce avian presence will depend on the targeted species. [ABSTRACT FROM AUTHOR]

We undertook the first study systematically evaluating the risk of Anisakis-sensitization in Croatian fish-processing workers and potential genetic susceptibility to anisakiasis. Anti-Anisakis IgE seroprevalence and risk factors for 600 employees of Croatian fish processing facilities and 466 blood donor controls, were assessed by indirect ELISA targeted with: recombinant Ani s 1 and Ani s 7 allergens, an Anisakis crude extract, the commercial ImmunoCAP kit, and questionnaires. Genetic susceptibility to anisakiasis was evaluated by genotypisation of human leukocytes alleles (HLA). Anti-Anisakis seropositive and a fraction of negative subjects were also assessed by ELISA and Western Blot (WB) for IgG seroprevalence to Trichinella spp. Overall, the observed anti-Anisakis seroprevalence inferred by indirect ELISA was significantly higher in fish processing workers (1.8%, 95% CI 0.9–3.3%) compared to the controls (0%, 0–0.8%). Seven out of 11 Ani s 1 and Ani s 7-positives and none of selected 65 negative sera, tested positive on whole-Anisakis extract (ImmunoCAP), whereas Anisakis crude extract ELISA detected 3.9% (2.4–6.0%) seropositives in fish processing workers, three (14%) of which showed IgE reactivity to milk proteins. The highest risk associated with Anisakis-sensitization among workers was fishing in the free time, rather than any of attributes related to the occupational exposure. Although no association was observed between anti-Anisakis seropositivity and wearing gloves or protective goggles, the majority of workers (92%) wore protective gloves, minimizing the risk for Anisakis sensitization via skin contact. Six HLA alleles within DRB1 gene were significantly associated with seropositivity under dominant, allelic or recessive models. All sera confirmed negative for anti-Trichinella spp. IgG. The study exhaustively covered almost all marine fish processing workers in Croatia, reflecting real-time Anisakis sensitization status within the industry, already under the influence of wide array of allergens. Author summary: Anisakiasis is a human disease caused by ingestion of live Anisakis spp. larvae by raw seafood. Fish processing and aquaculture workers (approximately 60 million people world-wide) are at occupational risk of becoming sensitized to Anisakis. This is the first study systematically evaluating the risk of Anisakis-sensitization in Croatian fish-processing workers and potential genetic susceptibility to anisakiasis in the analysed population. Observed seroprevalence was significantly higher in fish processing workers (1.8%) compared to the controls (0%). Surprisingly, the highest risk associated with Anisakis-sensitization among workers was fishing in their free time, rather than any of attributes related to the occupational exposure. While no association was observed between anti-Anisakis seropositivity and wearing gloves or protective goggles, the majority of workers (92%) wore protective gloves, minimizing the risk for Anisakis sensitization via skin contact. Additionally, seroprevalence to another important food-borne helminth, Trichinella spp. assessed in all Anisakis-positive subjects showed to be negative. Almost all marine fish processing workers in Croatia were part of this research, reflecting real-time Anisakis-sensitization status within the industry. This sets a baseline for the future tracking of sensitization in the sector already under the influence of wide array of allergens. [ABSTRACT FROM AUTHOR]

Albinism is the most common color variation described in fish and is characterized by a white or yellow phenotype according to the species. In rainbow trout Oncorhynchus mykiss, aside from yellow-albino phenotypes, cobalt blue variants with autosomal, recessive inheritance have also been reported. In this study, we investigated the inheritance pattern and chromatophores distribution/abundance of cobalt blue trouts obtained from a local fish farm. Based on crosses with wild-type and dominant yellow-albino lines, we could infer that cobalt blue are dominant over wild-type and co-dominant in relation to yellow-albino phenotype, resulting in a fourth phenotype: the white-albino. Analysis of chromatophores revealed that cobalt blue trouts present melanophores, as the wild-type, and a reduced number of xanthophores. As regards to the white-albino phenotype, they were not only devoid of melanophores but also presented a reduced number of xanthophores. Cobalt blue and white-albino trouts also presented reduced body weight and a smaller pituitary gland compared to wild-type and yellow-albino phenotypes. The transcription levels of tshb and trh were up regulated in cobalt blue compared to wild type, suggesting the involvement of thyroid hormone in the expression of blue color. These phenotypes represent useful models for research on body pigmentation in salmonids and on the mechanisms behind endocrine control of color patterning. [ABSTRACT FROM AUTHOR]

Biotechnology can provide innovative and efficient tools to support sustainable development of aquaculture. It is generally accepted that use of the term ‘genetically modified’ causes controversy and conflict among consumers, but little is known about how using the term ‘biotechnology’ as a salient feature on product packaging affects consumer preferences. In an online discrete choice experiment consisting of two treatments, a set of 1005 randomly chosen Swedish consumers were surveyed about use of hormone and triploidization sterilization techniques for salmonids. The information given to the treatment group included an additional sentence stating that the triploidization technique is an application of biotechnology, while the control group received the same text but without reference to biotechnology. Analysis using a hierarchical Bayes approach revealed significant consumer reactions to the term biotechnology. When the term was included in information, variation in consumer willingness-to-pay (WTP) estimates increased significantly. Moreover, some participants were dissuaded towards an option guaranteeing no biotechnological intervention in production of fish. These results have multiple implications for research and for the food industry. For research, they indicate the importance of examining the distribution of variation in WTP estimates for more complete characterization of the effects of information on consumer behavior. For the food industry, they show that associating food with biotechnology creates more variability in demand. Initiatives should be introduced to reduce the confusion associated with the term biotechnology among consumers. [ABSTRACT FROM AUTHOR]

In this study we attempted to determine the effect of various feeding methods (bottom and surface feeding) used in the hatchery, on the survival and growth rates of hatchery-reared sea trout (Salmo trutta trutta L.) in the wild. Rearing was performed in two variants: a bottom-fed group (BFG) and a surface-fed group (SFG). At the end of the rearing time, we observed that BFG fish gathered at the bottom of tank, as opposed to SFG fish, which swam in the whole water column. After 4 weeks of rearing, the fish were released into two similar streams. After about 2 months the fish were captured and the foodbase of the streams were examined. 30 fish from each group have been randomly selected for stomach contents analysis. In the shallow stream the growth rates were better for the BFG fish than the SFG and also a significantly higher number of typical benthic taxa was found in stomachs of the BFG fish than the SFG fish. In the deeper stream more food was found in the stomachs of the SFG fish than in the BFG fish. The analyzed results showed that factors such as stream depth, current velocity, and turbulence can also affect the rearing success of juvenile salmonids in hatchery streams. Bottom feeding fish during rearing has a positive impact only on the fish in shallow watercourses, where there is no turbulence, and the food is not carried by the current drift or washed out from the bottom into the drift. [ABSTRACT FROM AUTHOR]

DNA methylation has frequently been implicated in sex determination and differentiation in teleost species. In order to detect the DNA methylation patterns established during sexual differentiation in tiger pufferfish T. rubripes, we performed comprehensive whole genome methylation sequencing and analyses of the gonads of male, female, and pseudo male. We obtained a total of 33.12, 32.44, and 31.60 Gb clean data for male, female, and pseudo male, with a sequencing depth of 66.44×, 60.47× and 54.86×, respectively. The methylation level of cytosine (C) residues in the genomic DNA from gonads was 11.016%, 10.428%, and 11.083% in male, female, and pseudo male, respectively. More than 65% of C methylation was at CpG sites, and less than 1% was at CHG and CHH sites. In each regulatory element, there were low methylation levels on both sides of the transcription start site, and higher methylation levels in exons, introns, and downstream of genes. The highest mCpG was on chromosome 8 and the lowest mCpG was on chromosome 5. Comparisons of whole-genome DNA methylation between pairs of samples revealed that there were 3,173 differentially methylated regions (DMRs) between female and male, and 3,037 DMRs between male and pseudo male, corresponding to 0.232% and 0.223% of the length of the genome, respectively. There were only 1,635 DMRs between female and pseudo male, representing 0.127% of the length of the genome. A number of differentially methylated genes (DMGs) related to sex determination and differentiation were selected, such as amhr2 and pfcyp19a. After Bisulfite Sequencing PCR (BSP) verification, amhr2 was exhibited low methylation level in normal males and pseudo male, and high methylation level in normal females but pfcyp19a showed low methylation level in normal females and high methylation level in normal males and pseudo males. These results provide information about the molecular epigenetic mechanisms of DNA methylation during low-temperature induced masculinization of tiger pufferfish, and increase our understanding of the mechanisms of sex determination and differentiation in this important aquaculture fish species. [ABSTRACT FROM AUTHOR]

Environmental changes can modify the phenotypic characteristics of populations, which in turn can influence their evolutionary trajectories. In ectotherms like fishes, temperature is a particularly important environmental variable that is known to have significant impacts on the phenotype. Here, we raised specimens of the surface ecomorph of Astyanax mexicanus at temperatures of 20°C, 23°C, 25°C, and 28°C to examine how temperature influenced vertebral number and body shape. To increase biological realism, specimens were also subjected to two water turbulence regimes. Vertebral number was counted from x-rays and body shape variation was analysed using geometric morphometric methods. Temperature significantly impacted mean total vertebral number, which increased at the lowest and highest temperatures. Fish reared at lower temperatures had relatively more precaudal vertebrae while fish reared at higher temperatures had relatively more caudal vertebrae. Vertebral anomalies, especially vertebral fusions, were most frequent at the extreme temperature treatments. Temperature significantly impacted body shape as well, with fish reared at 20°C being particularly divergent. Water turbulence also impacted body shape in a generally predictable manner, with specimens reared in high turbulence environments being more streamlined and having extended dorsal and anal fin bases. Variation in environmental variables thus resulted in significant changes in morphological traits known to impact fish fitness, indicating that A. mexicanus has the capacity to exhibit a range of phenotypic plasticity when challenged by environmental change. Understanding the biochemical mechanisms underlying this plasticity and whether adaptive plasticity has influenced the evolutionary radiation of the Characidae, are major directions for future research. [ABSTRACT FROM AUTHOR]

In fish, the circadian clock represents a key regulator of many aspects of biology and is controlled by combinations of abiotic and biotic factors. These environmental factors are frequently manipulated in fish farms as part of strategies designed to maximize productivity. The flatfish turbot, Scophthalmus maximus, represents one of the most important species within the aquaculture sector in Asia and Europe. Despite the strategic importance of this species, the function and regulation of the turbot circadian system remains poorly understood. Here, we have characterized the core circadian clock genes, clock1, per1, per2 and cry1 in turbot and have studied their daily expression in various tissues under a range of lighting conditions and feeding regimes. We have also explored the influence of light and feeding time on locomotor activity. Rhythmic expression of the four core clock genes was observed in all tissues studied under light dark (LD) cycle conditions. Rhythmicity of clock gene expression persisted upon transfer to artificial free running, constant conditions confirming their endogenous circadian clock control. Furthermore, turbot showed daily cycles of locomotor activity and food anticipatory activity (FAA) under LD and scheduled-feeding, with the activity phase as well as FAA coinciding with and being dependent upon exposure to light. Thus, while FAA was absent under constant dark (DD) conditions, it was still detected in constant light (LL). In contrast, general locomotor activity was arrhythmic in both constant darkness and constant light, pointing to a major contribution of light, in concert with the circadian clock, in timing locomotor activity in this species. Our data represents an important contribution to our understanding of the circadian timing system in the turbot and thereby the optimization of rearing protocols and the improvement of the well-being of turbot within fish farming environments. [ABSTRACT FROM AUTHOR]

Background: In 2015, Singapore had the first and only reported foodborne outbreak of invasive disease caused by the group B Streptococcus (GBS; Streptococcus agalactiae). Disease, predominantly septic arthritis and meningitis, was associated with sequence type (ST)283, acquired from eating raw farmed freshwater fish. Although GBS sepsis is well-described in neonates and older adults with co-morbidities, this outbreak affected non-pregnant and younger adults with fewer co-morbidities, suggesting greater virulence. Before 2015 ST283 had only been reported from twenty humans in Hong Kong and two in France, and from one fish in Thailand. We hypothesised that ST283 was causing region-wide infection in Southeast Asia. Methodology/Principal findings: We performed a literature review, whole genome sequencing on 145 GBS isolates collected from six Southeast Asian countries, and phylogenetic analysis on 7,468 GBS sequences including 227 variants of ST283 from humans and animals. Although almost absent outside Asia, ST283 was found in all invasive Asian collections analysed, from 1995 to 2017. It accounted for 29/38 (76%) human isolates in Lao PDR, 102/139 (73%) in Thailand, 4/13 (31%) in Vietnam, and 167/739 (23%) in Singapore. ST283 and its variants were found in 62/62 (100%) tilapia from 14 outbreak sites in Malaysia and Vietnam, in seven fish species in Singapore markets, and a diseased frog in China. Conclusions: GBS ST283 is widespread in Southeast Asia, where it accounts for a large proportion of bacteraemic GBS, and causes disease and economic loss in aquaculture. If human ST283 is fishborne, as in the Singapore outbreak, then GBS sepsis in Thailand and Lao PDR is predominantly a foodborne disease. However, whether transmission is from aquaculture to humans, or vice versa, or involves an unidentified reservoir remains unknown. Creation of cross-border collaborations in human and animal health are needed to complete the epidemiological picture. [ABSTRACT FROM AUTHOR]

Decoupled aquaponic systems have the potential to become one of the most effective sustainable production systems for the combined production of animal protein and plant crops. Here, recirculating aquaculture systems for fish production are combined with hydroponics for soilless plant production thereby recycling dissolved nutrients derived from metabolism of the fish. The aim of the present study was to characterize hydroponic lettuce production using conventional nutrient solution in comparison with decoupled aquaponics using the nutrient rich fish water as basis for the nutrient solution being supplemented by missing nutrients. In addition, one aquaponic treatment became disinfected in order to assess any occurring advantage of the aquaponics derived fish water. For evaluation the temperature, electrical conductivity, pH, and the mineral composition of the nutrient solution, as well as colony forming units in the fish water were monitored. Additionally, plant growth (fresh and dry weight, number and area of leaves) and quality parameters of lettuce leaves (nitrate, mineral content, phenolic compounds) were examined. Carbon sources and microorganisms derived from fish water seem to have neither beneficial nor detrimental effects on plant growth in this study. Except for some differences in the mineral content of the lettuce leaves, all other quality parameters were not significantly different. The use of aquaponic fish water saved 62.8% mineral fertilizer and fully substituted the required water for the nutrient solution in comparison to the control. Additionally, the reduced fertilizer demand using decoupled aquaponics can contribute to reduce greenhouse gas emissions of an annual lettuce production site per ha by 72% due to saving the energy for fertilizer production. This study clearly demonstrates the huge potential of the innovative approach of decoupled aquaponics to foster the transformation of our conventional agriculture towards sustainable production systems saving resources and minimizing emissions. [ABSTRACT FROM AUTHOR]

The zebrafish Danio rerio is a powerful model system to study the genetics of development and disease. However, maintenance of zebrafish husbandry records is both time intensive and laborious, and a standardized way to manage and track the large amount of unique lines in a given laboratory or centralized facility has not been embraced by the field. Here, we present FishNET, an intuitive, open-source, relational database for managing data and information related to zebrafish husbandry and maintenance. By creating a “virtual facility,” FishNET enables users to remotely inspect the rooms, racks, tanks, and lines within a given facility. Importantly, FishNET scales from one laboratory to an entire facility with several laboratories to multiple facilities, generating a cohesive laboratory and community-based platform. Automated data entry eliminates confusion regarding line nomenclature and streamlines maintenance of individual lines, while flexible query forms allow researchers to retrieve database records based on user-defined criteria. FishNET also links associated embryonic and adult biological samples with data, such as genotyping results or confocal images, to enable robust and efficient colony management and storage of laboratory information. A shared calendar function with email notifications and automated reminders for line turnover, automated tank counts, and census reports promote communication with both end users and administrators. The expected benefits of FishNET are improved vivaria efficiency, increased quality control for experimental numbers, and flexible data reporting and retrieval. FishNET’s easy, intuitive record management and open-source, end-user–modifiable architecture provides an efficient solution to real-time zebrafish colony management for users throughout a facility and institution and, in some cases, across entire research hubs. [ABSTRACT FROM AUTHOR]

Dietary insufficiencies have been well documented to decrease growth rates and survival (and therefore overall production) in fish aquaculture. By contrast, the effects of dietary insufficiencies on the sensory biology of cultured fish remains largely unstudied. Diets based solely on plant protein sources could have advantages over fish-based diets because of the cost and ecological effects of the latter, but plant proteins lack the amino acid taurine. Adequate levels of taurine are, however, necessary for the development of a fully functional visual system in mammals. As part of ongoing studies to determine the suitability of plant-based diets, we investigated the effects of normal and reduced taurine dietary levels on retinal anatomy and function in European sea bass (Dicentrarchus labrax). We could not demonstrate any effects of dietary taurine level on retinal anatomy, nor the functional properties of luminous sensitivity and temporal resolution (measured as flicker fusion frequency). We did, however, find an effect on spectral sensitivity. The peak of spectral sensitivity of individuals fed a 5% taurine diet was rightward shifted (i.e., towards longer wavelengths) relative to that of fish fed a 0% or 1.5% taurine diet. This difference in in spectral sensitivity was due to a relatively lower level of middle wavelength pigment (maximum absorbance .500 nm) in fish fed a 5% taurine diet. Changes in spectral sensitivity resulting from diets containing different taurine levels are unlikely to be detrimental to fish destined for market, but could be in fishes that are being reared for stock enhancement programs. [ABSTRACT FROM AUTHOR]

Although the relationship between the incorporation of an element into otoliths and the concentration of the element in water has been extensively investigated in many fish species, the interactive effects of multiple elements in water on the otolith incorporation of an element are not adequately explored or well understood. In this study, 16 treatments in triplicate using strontium (Sr; 1, 2, 3 and 4 times the ambient baseline, 6.5 mg l-1) and barium (Ba; 1, 2, 4 and 6 times the ambient baseline, 40 μg l-1) as categorical variables in an orthogonal design were established to evaluate the relative or interactive effects of water elements on otolith elemental incorporation in juvenile flounder Paralichthys olivaceus (from 15 to 116 days post hatching). The results revealed that otolith incorporation (Me:CaOtolith) of Sr and Ba were positively dependent on the concentrations of the elements in water (Me:CaWater). Overall, Sr was incorporated into otoliths more efficiently than was Ba, and the partition efficiency (DMe) of both elements decreased with increasing water elemental concentrations. Increasing Sr concentrations in water appeared to negatively affect the uptake of Ba into otoliths rather than facilitate it, as previously reported in fish reared in freshwater and brackish water, or showed no effect on fish in seawater. Conversely, the Ba concentration in water did not influence the otolith uptake of Sr, which agrees with the findings for other fish species. When applying otolith microchemistry to fish ecology studies, it is essential to cautiously address the interactive effects of multiple elements in the environment on otolith elemental incorporation. [ABSTRACT FROM AUTHOR]