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Condition indices aim to evaluate the physiological status of fish larvae by estimating both the level of starvation and potential of survival. Histological indices reveal direct effects of starvation whereas biochemical indices such as lipid classes or RNA:DNA ratios are used as proxies of condition, giving information on the amount of energy reserves and growth rate, respectively. We combined these three indices to evaluate ontogenetic variations of growth performance, lipid dynamics and nutritional condition of plaice larvae caught in the field during winter 2017 in the eastern English Channel and the Southern Bight of the North Sea. RNA:DNA ratios showed that larvae at the beginning of metamorphosis (stage 4) had a lower growth rate than younger individuals (stages 2 and 3). A significant increase in the proportion of triglycerides also occurred at stage 4, indicating energy storage. Histological indices indicated that most of the larvae were in good condition, even younger ones with low lipid reserves. There was, however, an increase in the proportion of healthy individuals over ontogeny, especially with respect to liver vacuoles which were larger and more numerous for stage 4 larvae. Combined together, these condition indices revealed the ontogenetic shift in the energy allocation strategy of plaice larvae. Young larvae (stages 2 and 3) primarily allocate energy towards somatic growth. The decrease in growth performance for stage 4 was not related to poor condition, but linked to a higher proportion of energy stored as lipids. Since the quantity of lipid reserves is particularly important for plaice larvae to withstand starvation during metamorphosis, this could be considered as a second critical period after the one of exogenous feeding for larval survival and recruitment success. [ABSTRACT FROM AUTHOR]

Precise knowledge of the health status of experimental fish is crucial to obtain high scientific and ethical standards in biomedical research. In addition to the use of sentinel fish, the examination of diseased fish is a fundamental part of all health monitoring concepts. PCR assays offer excellent sensitivity and the ability to test a broad variety of pathogenic agents in different sample types. Recently, it was shown that analysis of environmental samples such as water, sludge or detritus from static tanks can complement PCR analysis of fish and is actually more reliable for certain pathogens. In our study, we investigated whether the analysis of filtered water mixed with detritus of tanks including fish showing clinical signs of illness is suitable to complement health monitoring programs in recirculating systems. The obtained data indicate that pathogens such as Pseudoloma neurophilia or Myxidium streisingeri were exclusively or mainly found in fish, while mycobacteria were predominantly present in environmental samples. A combination of both sample types seems to be required for the detection of a broad range of infectious agents in zebrafish colonies using real-time PCR technology. [ABSTRACT FROM AUTHOR]

Ocean acidification and ocean warming (OAW) are simultaneously occurring and could pose ecological challenges to marine life, particularly early life stages of fish that, although they are internal calcifiers, may have poorly developed acid-base regulation. This study assessed the effect of projected OAW on key fitness traits (growth, development and swimming ability) in European sea bass (Dicentrarchus labrax) larvae and juveniles. Starting at 2 days post-hatch (dph), larvae were exposed to one of three levels of PCO2 (650, 1150, 1700 μatm; pH 8.0, 7.8, 7.6) at either a cold (15°C) or warm (20°C) temperature. Growth rate, development stage and critical swimming speed (Ucrit) were repeatedly measured as sea bass grew from 0.6 to ~10.0 (cold) or ~14.0 (warm) cm body length. Exposure to different levels of PCO2 had no significant effect on growth, development or Ucrit of larvae and juveniles. At the warmer temperature, larvae displayed faster growth and deeper bodies. Notochord flexion occurred at 0.8 and 1.2 cm and metamorphosis was completed at an age of ~45 and ~60 days post-hatch for sea bass in the warm and cold treatments, respectively. Swimming performance increased rapidly with larval development but better swimmers were observed in the cold treatment, reflecting a potential trade-off between fast grow and swimming ability. A comparison of the results of this and other studies on marine fish indicates that the effects of OAW on the growth, development and swimming ability of early life stages are species-specific and that generalizing the impacts of climate-driven warming or ocean acidification is not warranted. [ABSTRACT FROM AUTHOR]

Inducing unconsciousness in fish using electrical stunning prior to slaughter may improve fish welfare and fillet quality if such practises can be disseminated into wild capture fisheries. The objectives of this study were to: 1) evaluate if an established slaughter protocol consisting of dry electrical stunning (using a coupled AC/DC current at ≈ 110 Vrms) followed by chilling could be used to stun the wild captured species Atlantic mackerel (Scomber scombrus) unconscious within 0.5 s; 2) determine if death could be induced without consciousness recovery by longer duration stunning (5 s) combined with chilling in an ice/water slurry for 6 min; and 3) examine the extent of quality defects arising from the applied slaughter protocol. We determined consciousness by examination of behavioural responses in a standardised vitality assessment. Out of a sample of 10 mackerel, 9 were assumed to be rendered unconscious by the 0.5 s stun, as determined by the presence of tonic and/or clonic muscle cramping consistent with a general epileptic insult. Assumed unconsciousness was maintained throughout chilling treatment in all fish (n = 25) following a full stun of 5 s. All fish were assumed to have died as a result of the protocol. There was no evidence of spinal damage or haematoma quality defects post filleting. These results suggest that the examined protocol is effective at slaughtering mackerel in a manner consistent with good welfare and without inducing quality defects, but further research is required to verify the unconscious condition via electroencephalogram (EEG) and before the procedure can be applied in wild capture fisheries. [ABSTRACT FROM AUTHOR]

Tourism represents an important opportunity to provide sustainable funding for many ecosystems, including marine systems. Tourism that is reliant on aggregating predator species in a specific area using food provisioning raises questions about the long-term ecological impacts to the ecosystem at large? Here, using opportunistically collected video footage, we document that 61 different species of fish across 16 families are consuming tuna flesh at two separate shark dive tourism operations in the Republic of Fiji. Of these fish, we have resolved 55 to species level. Notably, 35 (63%) of the identified species we observed consuming tuna flesh were from ostensibly non-piscivorous fishes, including four Acanthuridae species, a group primarily recognized as browsers or grazers of algae and epibenthic detritus. Our results indicate that shark diving is having a direct impact on species other than sharks and that many species are facultatively expanding their trophic niches to accommodate the hyperabundance of resources provided by ecotourism. [ABSTRACT FROM AUTHOR]

The physical basis for fish schooling is examined using three-dimensional numerical simulations of a pair of swimming fish, with kinematics and geometry obtained from experimental data. Energy expenditure and efficiency are evaluated using a cost of transport function, while the effect of schooling on the stability of each swimmer is examined by probing the lateral force and the lateral and longitudinal force fluctuations. We construct full maps of the aforementioned quantities as functions of the spatial pattern of the swimming fish pair and show that both energy expenditure and stability can be invoked as possible reasons for the swimming patterns and tail-beat synchronization observed in real fish. Our results suggest that high cost of transport zones should be avoided by the fish. Wake capture may be energetically unfavorable in the absence of kinematic adjustment. We hereby hypothesize that fish may restrain from wake capturing and, instead, adopt side-to-side configuration as a conservative strategy, when the conditions of wake energy harvesting are not satisfied. To maintain a stable school configuration, compromise between propulsive efficiency and stability, as well as between school members, ought to be considered. [ABSTRACT FROM AUTHOR]

A subarctic fish community in mine-impacted Yellowknife Bay (Great Slave Lake, Northwest Territories, Canada) was investigated for biological and ecological processes controlling arsenic bioaccumulation. Total concentrations of arsenic, antimony, and metals were measured in over 400 fishes representing 13 species, and primary producers and consumers were included to characterize food web transfer. Yellowknife Bay had slightly more arsenic in surface waters (~3 μg/L) relative to the main body of Great Slave Lake (<1 μg/L), resulting in two-fold higher total arsenic concentrations in muscle of burbot (Lota lota), lake whitefish (Coregonus clupeaformis), and northern pike (Esox lucius). Other mining-associated contaminants, specifically antimony, lead, and silver, were typically below analytical detection in those fish species. No evidence was found for enhanced bioaccumulation of arsenic in long-lived, slow-growing subarctic fishes. Food web biodilution of total arsenic occurred between primary producers, aquatic invertebrates, and fish, although trophic position did not explain arsenic concentrations among fishes. Pelagic-feeding species had higher total arsenic concentrations compared to littoral fishes. Arsenic accumulated in subarctic fishes to comparable levels as fishes from lakes around the world with similar water arsenic concentrations. This first comprehensive study for a subarctic freshwater food web identified the importance of water exposure, biodilution, and habitat-specific feeding on arsenic bioaccumulation. [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]

Background: Most research into the health benefits of human-animal interaction has focused on species that interact physically with humans, such as dogs. This may be unsuitable for certain populations for reasons including accessibility and the risk of negative consequences to both the person and the animal. However, some research has associated viewing fish in aquariums with positive well-being outcomes; as there is no physical contact with the animal, this form of interaction carries less risk. At present, little is known about the specific benefits of human-fish interaction. Objectives: To explore current evidence relating to the psychological and physiological benefits of interacting with fish in aquariums. Methods: Systematic searches were conducted to identify relevant primary research of any design. All forms of interaction were considered, including keeping fish as companion animals and fish aquarium-based interventions. “Non-live” alternatives, such as videos, were also considered. This review was conducted according to a registered protocol (PROSPERO ID: CRD42018090466). Results: Nineteen studies were included. Two provided tentative evidence that keeping home aquaria is associated with relaxation. The remaining studies involved novel interactions with fish in home or public aquariums. Outcomes relating to anxiety, relaxation and/or physiological stress were commonly assessed; evidence was mixed with both positive and null findings. Preliminary support was found for effects on mood, pain, nutritional intake and body weight, but not loneliness. All studies had methodological issues and risk of bias was either high or unclear. Conclusions: Review findings suggest that interacting with fish in aquariums has the potential to benefit human well-being, although research on this topic is currently limited. Future research should aim to address gaps in the evidence, such as whether and how the type of human-fish interaction can influence well-being outcomes. Researchers should also aim to address the methodological concerns highlighted in this review. [ABSTRACT FROM AUTHOR]

Freshwater sulfide springs have extreme environmental conditions that only few vertebrate species can tolerate. These species often develop a series of morphological and molecular adaptations to cope with the challenges of life under the toxic and hypoxic conditions of sulfide springs. In this paper, we described a new fish species of the genus Jenynsia, Anablepidae, from a sulfide spring in Northwestern Argentina, the first in the family known from such extreme environment. Jenynsia sulfurica n. sp. is diagnosable by the lack of scales on the pre-pelvic area or the presence of a single row of scales, continuous or not, from the isthmus to the bases of the pelvic fins. Additionally, it presents a series of morphological and molecular characteristics that appear convergent with those seen in other fish species (e.g., Poeciliids) inhabiting sulfide springs. Most notably, J. sulfurica has an enlarged head and postorbital area compared to other fish of the genus and a prognathous lower jaw with a hypertrophied lip, thought to facilitate respiration at the air-water interface. Analyses of cox1 sequence showed that J. sulfurica has two unique mutations resulting in amino acid substitutions convergent to those seen in Poeciliids from sulfide springs and known to provide a physiological mechanism related to living in sulfide environments. A phylogenetic analysis, including molecular and morphological characters, placed J. sulfurica as sister taxa to J. alternimaculata, a species found in nearby, non-sulfide habitats directly connected to the sulfide springs. Thus, it can be inferred that the selection imposed by the presence of H2S has resulted in the divergence between these two species and has potentially served as a barrier to gene flow. [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]

Over the last decade, ocean temperature on the U.S. Northeast Continental Shelf (U.S. NES) has warmed faster than the global average and is associated with observed distribution changes of the northern stock of black sea bass (Centropristis striata). Mechanistic models based on physiological responses to environmental conditions can improve future habitat suitability projections. We measured maximum, standard metabolic rate, and hypoxia tolerance (Scrit) of the northern adult black sea bass stock to assess performance across the known temperature range of the species. Two methods, chase and swim-flume, were employed to obtain maximum metabolic rate to examine whether the methods varied, and if so, the impact on absolute aerobic scope. A subset of individuals was held at 30°C for one month (30chronic°C) prior to experiments to test acclimation potential. Absolute aerobic scope (maximum–standard metabolic rate) reached a maximum of 367.21 mgO2 kg-1 hr-1 at 24.4°C while Scrit continued to increase in proportion to standard metabolic rate up to 30°C. The 30chronic°C group exhibited a significantly lower maximum metabolic rate and absolute aerobic scope in relation to the short-term acclimated group, but standard metabolic rate or Scrit were not affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, calculated from Scrit as an estimate of potential aerobic scope, closely matched the measured factorial aerobic scope (maximum / standard metabolic rate) and declined with increasing temperature to a minimum below 3. This may represent a critical threshold value for the species. With temperatures on the U.S. NES projected to increase above 24°C in the next 80-years in the southern portion of the northern stock’s range, it is likely black sea bass range will continue to shift poleward as the ocean continues to warm. [ABSTRACT FROM AUTHOR]

Treated wastewater (TWW) constitutes a sustainable water resource and has been used for fish culture in some countries around the world, although there are no comprehensive data on the effect of TWW on fish growth and health in the context of aquaculture production. Our objectives were to examine how fish culture in TWW affected fish growth and fitness, as well as compliance with the international standards for safe consumption. Guppy (Poecilia reticulata) fingerlings were reared in 0%, 50% and 100% tertiary TWW (TTWW), from the age of five days, for a period of four months. In water analyses, 33 out of 67 tested organic micropollutants (OMPs) were detected in the TTWW samples at least once, at concentrations that are typically reported in domestic TTWW. Fish survival ranged between 77–80% and did not differ between treatment groups. Fish growth and mortality following challenge infection with Tetrahymena sp. (which ranged between 64–68%), were similar among treatment groups. Of tested immunological parameters, lysozyme and anti-protease was similar among treatments while complement activity was highest in the 50% TTWW-reared fish. No abnormalities were observed in the histopathological analysis. Levels of heavy metals, polychlorinated-biphenyls (PCBs) and organochlorines (OCs) in fish were below the detection limit and below the Food and Agriculture Organization of the United Nations (FAO) and the European Union EU maximal permitted levels in food fish. Results suggest that the yield of fish grown in TTWW is potentially similar to that in freshwater, and the produced fish comply with the standards of consumer safety. The results are in line with previous studies that examined the feasibility of TWW-fed aquaculture. [ABSTRACT FROM AUTHOR]

This goal of this study was to highlight the importance of minerals in the diet of fish for meeting micronutrient requirements in the human diet. First arsenic, calcium, cadmium, copper, iron, molybdenum, magnesium, manganese, sodium, phosphorus, potassium, selenium, and zinc concentrations of twelve commercially available tilapia samples were measured. The nutritional value of fillets in regard to their mineral content were assessed to establish potential health benefits or risks for consumers. The health benefit value of selenium was also calculated. Positive health benefit values indicate that tilapia fillets in the United States marketplace of this study do not pose health risks associated with mercury exposures. Selenium was the trace mineral of interest. After the market study, a seven-week fish feeding trial was conducted to study the influence of organic versus inorganic dietary selenium on Nile tilapia (Oreochromis niloticus). Fish were fed two different diets enriched with the same concentration (0.01g kg-1) of selenium in form of inorganic (sodium selenite) or organic (seleno-L-methionine) selenium in triplicate groups. There were no significant differences between growth and biometrics of fish fed different diets (p>0.05). At the end of trial twelve fish from each treatment were collected. Fillets of fish fed organic selenium had selenium concentrations of 0.55 ± 0.01 μg g-1 which were significantly (p<0.05) higher than fish fed inorganic selenium at levels of 0.22 ± 0.008 μg g-1 or fish samples from the marketplace with a selenium level of 0.2 ± 0.03 μg g-1. Fish fed organic selenium also had significantly higher (p<0.05) plasma and kidney selenium in comparison to fish fed inorganic selenium. No significant differences (p>0.05) were observed in glutathione peroxidase activities in either the plasma or liver of Nile tilapia in the different treatment groups. This study shows that organic selenium is a better option for production of Nile tilapia fillets rich in selenium. [ABSTRACT FROM AUTHOR]

Acute change in water temperature causes heavy economic losses in the aquaculture industry. The present study investigated the metabolic and molecular effects of acute thermal stress on black rockfish (Sebastes schlegelii). Gas chromatography time-of-flight mass spectrometry (GC-TOF-MS)-based metabolomics was used to investigate the global metabolic response of black rockfish at a high water temperature (27°C), low water temperature (5°C) and normal water temperature (16°C). Metabolites involved in energy metabolism and basic amino acids were significantly increased upon acute exposure to 27°C (P < 0.05), and no change in metabolite levels occurred in the low water temperature group. However, certain fatty acid levels were elevated after cold stress (P < 0.05), and this effect was not observed in the 27°C group, suggesting that acute high and low temperature exposures caused different physiological responses. Using quantitative real-time PCR, we analyzed the expression of ubiquitin (ub), hypoxia-inducible factor (hif), lactate dehydrogenase (ldh), and acetyl-CoA carboxylase (acac). Higher expression levels of ub, hif, and ldh (P < 0.05) were observed in the high water temperature group, but no changes in these expression levels occurred in the low water temperature group. Our findings provide a potential metabolic profile for black rockfish when exposed to acute temperature stress and provide some insights into host metabolic and molecular responses to thermal stress. [ABSTRACT FROM AUTHOR]

In social animals, morphological and behavioural traits may give to some individuals a stronger influence on the collective decisions, even in groups assumed to be leaderless such as fish shoals. Here, we studied and characterized the leadership in collective movements of shoals of zebrafish Danio rerio by observing groups of 2, 3, 5, 7 and 10 zebrafish swimming in a two resting sites arena during one hour. We quantified the number of collective departures initiated by each fish and the number of attempts that they made. To do so, we developed an automated pipeline that analysed the individual trajectories generated by the tracking software. For all shoal sizes, the leadership was distributed among several individuals. However, it was equally shared among all the fish in some shoals while other groups showed a more asymmetrical sharing of the initiation of collective departures. To quantify this distribution, we computed the entropy associated with the time series of the identity of all initiators for each experiment and confirmed the presence of a continuum between a homogeneous and a heterogeneous distribution of the leadership. While some fish led more departures than others, an individual analysis showed that all fish had actually the same success rate to lead the shoal out of a resting site after an attempt. Thus, some individuals monopolized the leadership by attempting more often than others to exit a resting site. Finally, we highlight that the intra-group ranking of a fish for the initiative is correlated to its intra-group ranking for the average speed with mobile individuals more prone to lead the shoal. These results demonstrate that the collective behaviour of a shoal can be mainly driven by a subset of individuals even in the absence of higher influence of a fish on its congeneers. [ABSTRACT FROM AUTHOR]

In many salmonid species, age and size at maturation is plastic and influenced by the interaction between genetic and environmental factors. Hatchery reared salmon often mature at an earlier age and smaller size than wild fish. Modern salmon conservation efforts have focused on managing the level of gene flow between hatchery and natural origin fish to minimize potential genotypic and phenotypic change. In salmonids, maturation probability is dependent on exceeding a genetically set threshold in growth rate and energetic status (and by association, body size) referred to as the probabalisitic maturation reaction norm (PMRN). Over fourteen years, we monitored the frequency of age-2 precocious male maturation (common term: age-2 minijack rate) and the PMRN of natural founder (FNDR), integrated natural-hatchery (INT), and segregated hatchery (SEG) broodlines of spring Chinook salmon, Oncorhynchus tshawytscha. The average age-2 minijack rate (± SEM) of the FNDR, INT and SEG broodlines was 48.2 ± 5.2%, 41.9 ± 3.6% and 30.9 ± 4.7%, respectively. Additionally, the PMRN WP 50 (predicted weight at 50% maturation) of the SEG broodline was significantly greater (20.5 g) than that of the FNDR/INT broodlines (18.2 g). We also conducted a common garden experiment exploring the effects of less than one [INT (0–1)], one [SEG (1)] or two [SEG (2)] generations of hatchery culture on the age-2 minijack rate and PMRN WP 50. Growth was not significantly different among broodlines, but age-2 minijack rates were significantly lower following two consecutive generations of hatchery culture: [INT (0–1): 68.3 ± 1.7%], [SEG (1): 70.3 ± 1.8%] and [SEG (2): 58.6 ± 0.4%] and the PMRN WP 50 was significantly higher by 6.1 g after two generations of SEG culture. These results indicate that managed gene flow reduces phenotypic divergence, but may serve to maintain potentially undesirably high age-2 minijack rates in salmon conservation hatchery programs. [ABSTRACT FROM AUTHOR]

The reliance of the aquafeed industry on marine resources has to be reduced by innovative approaches in fish nutrition. Thus, a three-factorial approach (fish oil reduced diet, phytochemical genistein, and temperature reduction) was chosen to investigate the interaction of effects on growth performance and tissue omega-3 long chain polyunsaturated fatty acid (LC-PUFA) levels in juvenile sea bream (Sparus aurata, 12.5 ± 2.2 g). Genistein is a phytoestrogen with estrogen-like activity and thus LC-PUFA increasing potential. A decrease in the rearing temperature was chosen based on the positive effects of low temperature on fish lipid quality. The experimental diets were reduced in marine ingredients and had a fish oil content of either 6% dry matter (DM; F6: positive control) or 2% DM (F2: negative control) and were administered in the plain variant or with inclusion of 0.15% DM genistein (F6 + G and F2 + G). The feeding trial was performed simultaneously at 23°C and 19°C. The results indicated that solely temperature had a significant effect on growth performance and whole body nutrient composition of sea bream. Nevertheless, the interaction of all three factors significantly affected the fatty acid compositions of liver and fillet tissue. Most importantly, they led to a significant increase by 4.3% of fillet LC-PUFA content in sea bream fed with the diet F6 + G in comparison to control fish fed diet F6, when both groups were held at 19°C. It is hypothesized that genistein can act via estrogen-like as well as other mechanisms and that the dietary LC-PUFA content may impact its mode of action. Temperature most likely exhibited its effects indirectly via altered growth rates and metabolism. Although effects of all three factors and of genistein in particular were only marginal, they highlight a possibility to utilize the genetic capacity of sea bream to improve tissue lipid quality. [ABSTRACT FROM AUTHOR]

Considering the divergent temperature habitats and morphological traits of four Percidae species: yellow perch (Perca flavescens), Eurasian perch (Perca fluviatilis), pike perch (Sander lucioperca), and ruffe (Gymnocephalus cernua), we stepped into the transcriptome level to discover genes and mechanisms that drive adaptation to different temperature environments and evolution in body shape. Based on 93,566 to 181,246 annotated unigenes of the four species, we identified 1,117 one-to-one orthologous genes and subsequently constructed the phylogenetic trees that are consistent with previous studies. Together with the tree, the ratios of nonsynonymous to synonymous substitutions presented decreased evolutionary rates from the D. rerio branch to the sub-branch clustered by P. flavescens and P. fluviatilis. The specific 93 fast-evolving genes and 57 positively selected genes in P. flavescens, compared with 22 shared fast-evolving genes among P. fluviatilis, G. cernua, and S. lucioperca, showed an intrinsic foundation that ensure its adaptation to the warmer Great Lakes and farther south, especially in functional terms like “Cul4-RING E3 ubiquitin ligase complex.” Meanwhile, the specific 78 fast-evolving genes and 41 positively selected genes in S. lucioperca drew a clear picture of how it evolved to a large and elongated body with camera-type eyes and muscle strength so that it could occupy the highest position in the food web. Overall, our results uncover genetic basis that support evolutionary adaptation of temperature and body shape in four Percid species, and could furthermore assist studies on environmental adaptation in fishes. [ABSTRACT FROM AUTHOR]

Bioengineering, which studies the principles and design of biological systems, is a field that has inspired the development of several technologies that are currently in use. In this work, we use concepts from the fish lateral line sensing mechanism and apply them to seismic imaging processing. The lateral line is a sensory system composed of an integrated array of mechanical sensors spanning along the fish body. We compare the array of sensors along body fish with the seismic acquisition, which employs an array of equally spaced identical mechanical sensors to image the Earth’s subsurface. In both situations, the mechanical sensors capture and process mechanical vibrations from the environment to produce useful information. We explore the strategy of using the low-pass and high-pass sensors schema of fish lateral line to improve the seismic technique. We use the full-wave inversion method to compare the conventional acquisition procedure of identical sensors with alternative sets of different sensors, which mimics the fish lateral line. Our results show that the alternate sensors arrangement surpasses the performance of the conventional acquisition method, using just half of the input information. The results point at an image processing technique that is computationally more efficient and economical than the usual seismic processing method. [ABSTRACT FROM AUTHOR]

Starvation is a common stress in fish. The underlying molecular mechanisms associated with growth depression caused by feeding restriction and compensatory growth are not well understood. We investigated the effect of fasting and refeeding on the transcriptome profiles of brain in juvenile S. hollandi using RNA-seq. A total of 4.73 × 108 raw reads were obtained from nine brain samples. De novo transcriptome assembly identified 387,085 unigenes with 2.1×109 nucleotides. A total of 936 annotated unigenes showed significantly differential expression among the control, fasting, and fasting-refeeding groups. The down-regulated differentially expressed genes (DEGs) during fasting were mainly associated with cell cycle, DNA replication, and mitosis. The up-regulated DEGs were mainly related to glucose and lipid metabolism, material transportation, and transcription factors. Most decreased DEGs during fasting were restored to normal levels after refeeding. Comparing with the control group, genes associated with protein synthesis, stimulus response, and carbohydrate metabolism were significantly over-expressed and pro-opio melanocortin (POMC) was down-regulated during the refeeding period. In conclusion, fish mobilized stored energetic materials and reduced energy consumption to prolong survival during fasting. After refeeding, the down-regulation of DEGs, e.g., POMC may be associated with compensatory growth. Up-regulation of DEGs related to ribosomal protein, stimulus response, and carbohydrate metabolism may contribute to eliminate negative effect of starvation on brain. This study provided the first transcriptome data related with impact of short-time starvation and refeeding in S. hollandi brains. [ABSTRACT FROM AUTHOR]

Temperature and individual egg size have been long studied in the development of fishes because of their direct effects on individual fitness. Here we studied the combined effects of three important factors for fish development, i.e. egg size, social environment and water temperature. Arctic charr (Salvelinus alpinus), a coldwater fish known to be phenotypically plastic, was used to investigate how these factors may affect growth and foraging behaviour of juvenile fish in a benign environment. We accounted for the social environment during early development by comparing fish raised in groups and in isolation. We examined the effect of egg size and a 2 °C difference on foraging behaviour, activity and growth a few weeks after first feeding. Growth trajectories of fish originating from large and small eggs were similar within each temperature: larger fish coming large eggs were at all time larger than smaller fish. There was no indication that small fish raised at a higher temperature grew faster than larger fish raised at a lower temperature. A 2 °C difference in temperature affected the behaviour of fish differently according to body size and/or social context. The foraging probability difference between fish raised in groups and fish briefly isolated was higher at 4.5 °C than at 6.5 °C for both size fish. Finally, there was no repeatability in foraging behaviour and mobility for isolated individuals. These results highlight the importance of small changes in temperature when evaluating growth and behaviour of fishes, and reveal the importance of considering the interaction of temperature with other factors, e.g. individual size and social environment, especially at early stages of development in fishes. We discuss these findings in the context of rapid changes in temperature and how temperature and its interaction with other factors may affect the phenotypes, ecology and evolution of coldwater fishes. [ABSTRACT FROM AUTHOR]

Background: Arteriovenous fistulas (AVF) for haemodialysis often experience early thrombosis and maturation failure requiring intervention and/or central venous catheter (CVC) placement. This secondary and exploratory analysis of the FAVOURED study determined whether omega-3 fatty acids (fish oils) or aspirin affected AVF usability, intervention rates and CVC requirements. Methods: In 567 adult participants planned for AVF creation, all were randomised to fish oil (4g/d) or placebo, and 406 to aspirin (100mg/d) or placebo, starting one day pre-surgery and continued for three months. Outcomes evaluated within 12 months included AVF intervention rates, CVC exposure, late dialysis suitability failure, and times to primary patency loss, abandonment and successful cannulation. Results: Final analyses included 536 participants randomised to fish oil or placebo (mean age 55 years, 64% male, 45% diabetic) and 388 randomised to aspirin or placebo. Compared with placebo, fish oil reduced intervention rates (0.82 vs 1.14/1000 patient-days, incidence rate ratio [IRR] 0.72, 95% confidence interval [CI] 0.54–0.97), particularly interventions for acute thrombosis (0.09 vs 0.17/1000 patient-days, IRR 0.53, 95% CI 0.34–0.84). Aspirin significantly reduced rescue intervention rates (IRR 0.45, 95% CI 0.27–0.78). Neither agent significantly affected CVC exposure, late dialysis suitability failure or time to primary patency loss, AVF abandonment or successful cannulation. Conclusion: Although fish oil and low-dose aspirin given for 3 months reduced intervention rates in newly created AVF, they had no significant effects on CVC exposure, AVF usability and time to primary patency loss or access abandonment. Reduction in access interventions benefits patients, reduces costs and warrants further study. [ABSTRACT FROM AUTHOR]

The three-spined stickleback (Gasterosteus aculeatus) is a small teleost fish that is ubiquitous across the Northern Hemisphere. Among the behaviours that have been characterised in this species is ritualized courtship, aggressiveness and parental behaviour. Whereas three-spined sticklebacks have been used for ecological, evolutionary, parasitological and toxicological research, its complex behavioural repertoire and experimental advantages have not been exploited for basic neuroscience research. The aim of the present study is to describe some innate behaviours of laboratory bred three-spined sticklebacks by using a battery of tests that have been developed and validated to model some aspects of human psychiatric disorders in zebrafish. We recorded mirror induced aggression, novel object boldness, shoaling, and anxiety-like behaviour using both the novel tank diving and the black-white preference tests. We show that behaviour of three-spined sticklebacks in these standard tests is remarkably similar to that of zebrafish and other species and can be altered by fluoxetine and buspirone. These findings highlight the potential of using three-spined sticklebacks for cross-species and translational studies. [ABSTRACT FROM AUTHOR]

Tench (Tinca tinca L.) has great economic potential due to its high rate of fecundity and long-life span. Population genetic studies based on allozymes, microsatellites, PCR-RFLP and sequence analysis of genes and DNA fragments have revealed the presence of Eastern and Western phylogroups. However, the lack of genomic resources for this species has complicated the development of genetic markers. In this study, the tench transcriptome and genome were sequenced by high-throughput sequencing. A total of 60,414 putative SNPs were identified in the tench transcriptome using a computational pipeline. A set of 96 SNPs was selected for validation and a total of 92 SNPs was validated, resulting in the highest conversion and validation rate for a non-model species obtained to date (95.83%). The validated SNPs were used to genotype 140 individuals belonging to two tench breeds (Tabor and Hungarian), showing low (FST = 0.0450) but significant (<0.0001) genetic differentiation between the two tench breeds. This implies that set of validated SNPs array can be used to distinguish the tench breeds and that it might be useful for studying a range of associations between DNA sequence and traits of importance. These genomic resources created for the tench will provide insight into population genetics, conservation fish stock management, and aquaculture. [ABSTRACT FROM AUTHOR]

The release of unwanted fish from purse seines whilst still in the water is termed slipping and may lead to significant mortality following release. The objective of this study was to determine the fish welfare implications of a new slipping methodology in which fish are released via a discharge opening formed in the bunt end of the purse seine net. Video analyses of collective and individual level fish behaviour were undertaken in the Norwegian mackerel and herring purse seine fisheries, to quantitively describe slipping behaviour and to determine its driving factors. The majority of fish escaped the purse seine with the schooling structure intact as part of large groups towards the end of slipping process, increasing their speed following escape. However, there was also a tendency (24% of all escapes) to escape in a manner likely to impact negatively upon their welfare, with a breakdown in schooling structure and physical contact with the fishing gear and conspecifics. The tendency to express such welfare compromising behaviour was higher for mackerel than for herring, but was also influenced by the vessel releasing the fish, the amount of fish being slipped, how long the discharge opening had been open and the particular slipping event. These results provide important information for future science-based development of welfare friendly slipping practises. [ABSTRACT FROM AUTHOR]

Fish reproductive patterns are very diverse in terms of breeding frequency, mating system, sexual dimorphisms and selection, mate choice, spawning site choice, courtship patterns, spawning behaviors and parental care. Here we have compared the breeding behavior of the surface-dwelling and cave-dwelling morphs of the characiform A. mexicanus, with the goals of documenting the spawning behavior in this emerging model organism, its possible evolution after cave colonization, and the sensory modalities involved. Using infrared video recordings, we showed that cave and surface Astyanax spawning behavior is identical, occurs in the dark, and can be divided into 5 rapid phases repeated many times, about once per minute, during spawning sessions which last about one hour and involve one female and several males. Such features may constitute “pre-adaptive traits” which have facilitated fish survival after cave colonization, and may also explain how the two morphs can hybridize in the wild and in the laboratory. Accordingly, cross-breeding experiments involving females of one morphotype and males of the other morphotype showed the same behavior including the same five phases. However, breeding between cavefish females and surface fish males was more frequent than the reverse. Finally, cavefish female pheromonal solution was able to trigger strong behavioral responses in cavefish males–but not on surface fish males. Lastly, egg production seemed higher in surface fish females than in cavefish females. These results are discussed with regards to the sensory modalities involved in triggering reproductive behavior in the two morphs, as well as its possible ongoing evolution. [ABSTRACT FROM AUTHOR]

Nile tilapia (Oreochromis niloticus) is an African freshwater fish that displays a genetic sex determination system (XX|XY) where high temperatures (above 32°C to 36.5°C) induce masculinization. In Nile tilapia, the thermosensitive period was reported from 10 to 30 days post fertilization. In their natural environment, juveniles may encounter high temperatures that are above the optimal temperature for growth (27–30°C). The relevance of the thermal sex reversal mechanism in a natural context remains unclear. The main objective of our study is to determine whether sexually undifferentiated juveniles spontaneously prefer higher, unfavorable temperatures and whether this choice skews the sex ratio toward males. Five full-sib progenies (from 100% XX crosses) were subjected to (1) a horizontal three-compartment thermal step gradient (thermal continuum 28°C– 32°C– 36.5°C) during the thermosensitive period, (2) a control continuum (28°C– 28°C– 28°C) and (3) a thermal control tank (36.5°C). During the first days of the treatment, up to an average of 20% of the population preferred the masculinizing compartment of the thermal continuum (36.5°C) compared to the control continuum. During the second part of the treatment, juveniles preferred the lower, nonmasculinizing 32°C temperature. This short exposure to higher temperatures was sufficient to significantly skew the sex ratio toward males, compared to congeners raised at 28°C (from 5.0 ± 6.7% to 15.6 ± 16.5% of males). The proportion of males was significantly different in the thermal continuum, thermal control tank and control continuum, and it was positively correlated among populations. Our study shows for the first time that Nile tilapia juveniles can choose a masculinizing temperature during a short period of time. This preference is sufficient to induce sex reversal to males within a population. For the first time, behavior is reported as a potential player in the sex determination mechanism of this species. [ABSTRACT FROM AUTHOR]

Osteocytes, cells forming an elaborate network within the bones of most vertebrate taxa, are thought to be the master regulators of bone modeling, a process of coordinated, local bone-tissue deposition and removal that keeps bone strains at safe levels throughout life. Neoteleost fish, however, lack osteocytes and yet are known to be capable of bone modeling, although no osteocyte-independent modeling regulatory mechanism has so far been described. Here, we characterize a novel, to our knowledge, bone-modeling regulatory mechanism in a fish species (medaka), showing that although lacking osteocytes (i.e., internal mechanosensors), when loaded, medaka bones model in mechanically directed ways, successfully reducing high tissue strains. We establish that as in mammals, modeling in medaka is regulated by the SOST gene, demonstrating a mechanistic link between skeletal loading, SOST down-regulation, and intense bone deposition. However, whereas mammalian SOST is expressed almost exclusively by osteocytes, in both medaka and zebrafish (a species with osteocytic bones), SOST is expressed by a variety of nonosteocytic cells, none of which reside within the bone bulk. These findings argue that in fishes (and perhaps other vertebrates), nonosteocytic skeletal cells are both sensors and responders, shouldering duties believed exclusive to osteocytes. This previously unrecognized, SOST-dependent, osteocyte-independent mechanism challenges current paradigms of osteocyte exclusivity in bone-modeling regulation, suggesting the existence of multivariate feedback networks in bone modeling—perhaps also in mammalian bones—and thus arguing for the possibility of untapped potential for cell targets in bone therapeutics. [ABSTRACT FROM AUTHOR]

Hydropeaking is the rapid change in the water flow downstream of a hydropower plant, driven by changes in daily electricity demand. These fluctuations may produce negative effects in freshwater fish. To minimize these impacts, previous studies have proposed habitat enhancement structures as potential mitigation measures for salmonids. However, the recommendation of these mitigation measures for cyprinids remains scarce and their effects unknown. In this study, the effects of potential habitat mitigation structures under simulated hydropeaking and base-flow conditions are examined for Iberian barbel (Luciobarbus bocagei) in an indoor flume. Solid triangular pyramids and v-shaped structures were evaluated as potential flow-refuging areas and compared with a configuration without structures. A novel, interdisciplinary approach is applied to investigate individual and group responses to rapidly changing flows, by assessing physiological (glucose and lactate), movement behaviour (structure use, sprints and drifts) and the pressure distribution using a fish-inspired artificial lateral line flow sensor. The major findings of this study are four-fold: 1) Under hydropeaking conditions, the v-shaped structures triggered a lactate response and stimulated individual structure use, whereas solid structures did not elicit physiological adjustments and favoured individual and group structure use. Overall, both solid structures and their absence stimulated sprints and drifts. 2) The hydrodynamic conditions created in hydropeaking did not always reflect increased physiological responses or swimming activity. 3) Each event-structure combination resulted in unique hydrodynamic conditions which were reflected in the different fish responses. 4) The most relevant flow variable measured was the pressure asymmetry, which is caused by the vortex size and shedding frequency of the structures. Considering the non-uniform nature of hydropeaking events, and the observation that the fish responded differently to specific flow event-structure combinations, a diverse set of instream structures should be considered for habitat-based hydropeaking mitigation measures for Iberian barbel. [ABSTRACT FROM AUTHOR]

Large numbers of lumpfish are produced for the Norwegian salmon industry and are used to combat sea lice infestations. Periodically high mortality of farmed lumpfish demonstrates the need to improve farming conditions and animal welfare. As part of such efforts, the present work tested the efficacy of three anaesthetic chemicals on lumpfish fries (average weight of 0.97 g). The anaesthetic impact from salinity (15 ppt–18 ppt), temperature (12°C versus 7 and 18°C), and fasting conditions (three days) was also examined. Surgical anaesthesia was induced within 3 to 5 min (preferred time) at concentrations of 18 mg/L (Aqui-S), 37.5 mg/L (Benzoak), and 60 mg/L (buffered MS-222). Safety margins were regarded as low when using Aqui-S; therefore, this chemical was not considered suitable for prolonged exposures. The lumpfish made a rapid recovery from both Benzoak and MS-222 even after 20 min of exposure. A 6°C increase in exposure temperature (reaching 18°C) was found to delay or inhibit recovery. The effect of a 5°C decrease (down to 7°C) significantly reduced induction time for MS-222 and was insignificant for Aqui-S, while it prolonged Benzoak induction time significantly and gave a longer recovery period. Fasting resulted in 70% recovery after 20 min of Aqui-S exposure compared to 0% in fed fish but had only minor effects on Benzoak and MS-222. Use of brackish water (15 ppt–18 ppt) gave 20% recovery from Aqui-S and significantly shorter recovery time from MS-222 exposure, while the effects on Benzoak were insignificant. [ABSTRACT FROM AUTHOR]

The effects of social hierarchies (dominant/subordinate individuals), such as aggressiveness, feeding order, and territoriality, are some of the characteristics used for describing fish behaviour. Social hierarchy patterns are still poorly understood in European-reared sea bass (Dicentrarchus labrax). In this work, we examine the social interactions among captive fish integrating behavioural and physiological profiles. Groups of three fish with EMG (electromyogram) radio transmitters were monitored for two weeks via video recording. Plasma levels of cortisol, glucose, lactate and lysozyme as well as haematological parameters such as haemoglobin, haematocrit and RBCC (red blood cell count) were measured at the beginning and end of the experiments. Behaviour and muscle activity were monitored daily. The results highlighted that the social hierarchic order was established after one to two days, and it was maintained throughout the experimental period. Dominant and subordinate fish (ß and γ) showed significant differences in muscle activity, hormonal profile (cortisol), aspecific immunity (lysozyme), carbohydrate metabolism (lactate) and behavioural patterns (food order and aggressiveness). This holistic approach helps to provide insights into the physiological status of the subordinate (ß and γ) and dominant individuals. These data have wide implications for aquaculture practice. [ABSTRACT FROM AUTHOR]

An anesthetic protocol was optimized for microinjection-related handling of Siberian sturgeon (Acipenser baerii; Acipenseriformes) prolarvae, an extant primitive fish species commonly grown in aquaculture. Comparative examinations of three selected anesthetics (clove oil, lidocaine, and MS-222) with a dosage regime of 50, 100, 200, and 400 mg/L indicated that MS-222 was the most efficient agent for Siberian sturgeon prolarvae, as evidenced by the fast induction of anesthesia with quick and uniform recovery. Meanwhile, clove oil should be avoided, due to prolonged recovery times varying widely between individuals. None of the tested anesthetics significantly affected prolarval viability at any of the dosage regimes tested in this study. Based on an analysis of the duration of an unconscious state in air, we recommend a dose of 200 mg/L MS-222 for microinjection. Recovery time after use of this dose was influenced by the prolarval age and the development of gills, in which prolarvae older than 3 days after hatching required longer recovery times than did younger prolarvae. Post-recovery behavioral assessment showed no apparent difference between MS-222-anesthetized and non-anesthetized prolarvae in their swimming behavior and phototactic responses. Applicability of currently developed anesthetic protocol using MS-222 in larval microinjection was demonstrated with the injection of a visible dye to the anesthetized prolarvae, followed by the analysis of post-recovery viability. Taken together, the present anesthetic protocol based on 200 mg/L of MS-222 could provide researchers with practical usefulness with good safety margins for the micromanipulation and other related handlings of Siberian sturgeon prolarvae. [ABSTRACT FROM AUTHOR]

Pacific Halibut (Hippoglossus stenolepis) support culturally and economically important fisheries in the Gulf of Alaska, though recent decreases in mean size-at-age have substantially reduced fishery yields, generating concerns among stakeholders and resource managers. Among the prevailing hypotheses for reduced size-at-age is intensified competition with Arrowtooth Flounder (Atheresthes stomias), a groundfish predator that exhibited nearly five-fold increases in biomass between the 1960s and mid-2010s. To assess the potential for competition between Pacific Halibut and Arrowtooth Flounder, we evaluated their degree of spatiotemporal and dietary overlap in the Gulf of Alaska using bottom trawl survey and food habits data provided by the Alaska Fisheries Science Center (NOAA; 1990 to 2017). We restricted analyses to fish measuring 30 to 69 cm fork length and used a delta modeling approach to quantify species-specific presence-absence and catch-per-unit-effort as a function of survey year, tow location, depth, and bottom temperature. We then calculated an index of spatial overlap across a uniform grid by multiplying standardized predictions of species’ abundance. Dietary overlap was calculated across the same uniform grid using Schoener’s similarity index. Finally, we assessed the relationship between spatial and dietary overlap as a measure of resource partitioning. We found increases in spatial overlap, moving from east to west in the Gulf of Alaska (eastern: 0.13 ± 0.20; central: 0.21 ± 0.11; western: 0.31 ± 0.13 SD). Dietary overlap was low throughout the study area (0.13 ± 0.20 SD). There was no correlation between spatial and dietary overlap, suggesting an absence of resource partitioning along the niche dimensions examined. This finding provides little indication that competition with Arrowtooth Flounder was responsible for changes in Pacific Halibut alHHsize-at-age in the Gulf of Alaska; however, it does not rule out competitive interactions that may have affected resource use prior to standardized data collection or at different spatiotemporal scales. [ABSTRACT FROM AUTHOR]

In nature, a multitude of both abiotic and biotic stressors influence organisms with regard to their overall fitness. Stress responses that finally impair normal biological functions may ultimately result in consequences for whole populations. This study focused on the metabolic response of the intertidal rock pool fish Gobius paganellus towards simulated predation risk. Individuals were exposed to a mixture of skin extracts from conspecifics and chemical alarm cues from a top predator, Octopus vulgaris. Oxygen consumption rates of single fish were measured to establish standard (SMR) and routine metabolic rates (RMR) of G. paganellus, and to address the direct response towards simulated predation risk, compared to handling and light stress. The SMR of G. paganellus (0.0301 ± 0.0081 mg O2 h-1 g-1 WW) was significantly lower than the RMR (0.0409 ± 0.0078 mg O2 h-1 g-1 WW). In contrast to increased respiration due to handling and light stress, the exposure to chemical predation cues induced a significant reduction in oxygen consumption rates (0.0297 ± 0.0077 mg O2 h-1 g-1 WW). This metabolic suppression was interpreted as a result of the stereotypic freezing behaviour as antipredator response of gobiid fish. Results underline the importance of biotic interactions in environmental stress assessments and predation as a biotic factor that will provide more realistic scenarios when addressing stress impacts in tidal rock pool organisms. [ABSTRACT FROM AUTHOR]

Global environmental change has the potential to disrupt well established species interactions, with impacts on nutrient cycling and ecosystem function. On coral reefs, fish living within the branches of coral colonies can promote coral performance, and it has been hypothesized that the enhanced water flow and nutrients provided by fish to corals could ameliorate coral bleaching. The aim of this study was to evaluate the influence of small, aggregating damselfish on the health of their host corals (physiology, recovery, and survival) before, during, and after a thermal-bleaching event. When comparing coral colonies with and without fish, those with resident fish exhibited higher Symbiodinium densities and chlorophyll in both field and experimentally-induced bleaching conditions, and higher protein concentrations in field colonies. Additionally, colonies with damselfish in aquaria exhibited both higher photosynthetic efficiency (FV/FM) during bleaching stress and post-bleaching recovery, compared to uninhabited colonies. These results demonstrate that symbiotic damselfishes, and the services they provide, translate into measureable impacts on coral tissue, and can influence coral bleaching susceptibility/resilience and recovery. By mediating how external abiotic stressors influence coral colony health, damselfish can affect the functional responses of these interspecific interactions in a warming ocean. [ABSTRACT FROM AUTHOR]

It is well known in aquaculture that hyperthermic perturbations may cause skeleton malformations in fish, but this phenomenon has rarely been documented in wild species. One rare location where thermal pollution has increased the proportion of malformed fish in wild population is in the waters near the Kuosheng Nuclear Power Plant in Taiwan. At this site, the threshold temperature and critical exposure time for inducing deformations have not been previously determined. In addition, it was unclear whether juvenile fish with thermal-induced malformations are able to recover when the temperature returns below the threshold. In the present study, juvenile largescale mullet (Planiliza macrolepis) were kept at temperatures ranging from 26°C and 36°C for 1–4 weeks, after which malformed fish were maintained at a preferred temperature of 26°C for another 8 weeks. The vertebrae bending index (VBI) of fish was increased after 2 weeks at 36°C, and deformed vertebral columns were detected by radiography after 4 weeks. However, malformations were not observed in groups kept at or below 34°C. Moreover, at the end of the recovery period, both the VBI and the vertebrae malformations had returned to normal. The results of this study may help to more precisely determine potential environmental impacts of thermal pollution and raise the possibility that the capacity for fish vertebrae to recover from the impacts of chronic thermal exposures may be an important consideration in marine fish conservation. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are a class of small non-coding RNAs which are known to posttranscriptionally regulate the expression of most genes in both animals and plants. Meanwhile, studies have shown that numbers of miRNAs are present in body fluids including the plasma. Despite the mode of action of these circulating miRNAs still remains unknown, they have been found to be promising biomarkers for disease diagnosis, prognosis and response to treatment. In order to evaluate the potential of miRNAs as non-invasive biomarkers in aquaculture, a time-course experiment was implemented to investigate the postprandial regulation of miRNAs levels in liver and plasma as well as the hepatic expression of genes involved in cholesterol metabolism. We showed that miR-1, miR-33a, miR-122, miR-128 and miR-223 were expressed in the liver of rainbow trout and present at detectable level in the plasma. We also demonstrated that hepatic expression of miR-1, miR-122 and miR-128 were regulated by feed intake and reached their highest levels 12 hours after the meal. Interestingly, we observed that circulating levels of miR-128 and miR-223 are subjected to postprandial regulations similar to that observed in their hepatic counterparts. Statistical correlations were observed between liver and plasma for miR-128 and miR-223 and between hepatic and circulating miR-122, miR-128 and miR-223 and expression of genes related to cholesterol synthesis and efflux or glucose phosphorylation. These results demonstrated that circulating miR-122, miR-128 and miR-223 are potential biomarkers of cholesterol metabolism in rainbow trout. [ABSTRACT FROM AUTHOR]

We have created a new, fast-growing strain of common carp with higher unsaturated fatty acid content in muscle. To better understand the impacts of gene regulation in intestinal tissue on growth and unsaturated fatty acid content, we conducted a comparative RNA-Seq transcriptome analysis between intestine samples of Selected and Control groups (and corroborated selected results by PCR). After eight weeks of cage culture, weight gain of the Selected group was 20.84% higher. In muscles of the control group, monounsaturated fatty acids (FAs) were more abundant, whereas polyunsaturated FAs were more abundant in muscles of the Selected group. In total, we found 106 differentially expressed genes (DEGs) between the two groups. Only the endocytosis pathway was significantly enriched in DEGs, with two upregulated genes: il2rb and ehd1. The latter is involved in the growth hormone/insulin-like growth factor (Gh/Igf) axis, which plays a key role in the regulation of growth in animals. tll2, which is known to be associated with intestinal regeneration, was extremely highly upregulated in both transcriptomic (infinite) and qPCR (610.70) analyses. Two of the upregulated genes are associated with the fatty acid metabolism, several genes are likely to be indicators of heightened transcription levels, several are associated with metabolic and developmental roles, several with neuronal functions (including two with vision), several with the immune system, and two downregulated genes with the development of vasculature. The higher growth rate of the Selected group is likely to be at least partially attributed to increased endocytosis efficiency and genetically-driven behavioural differences (higher aggression levels). There are some indications that this new strain might have slightly impaired immune responses, and a higher propensity for inherited diseases leading to sight impairment, as well for neurodegenerative diseases in general, but these indications still need to be confirmed. [ABSTRACT FROM AUTHOR]

Models simulating the in vitro digestive hydrolysis of nutrients by different animal species are frequently used to obtain a better understanding of factors affecting this process. Optimization algorithm of a model may be used to prospect the more favourable combination of selected factors resulting in the higher performance. This study was conducted to determine the combination of factors (pH, enzyme:substrate ratio, and reaction time) leading to highest bioavailability of proteins and carbohydrates in the gilthead seabream gastrointestinal tract. Besides, a novel multi-objective algorithm, desirability function, was introduced for optimization of the digestive hydrolysis of nutrients within the simulated gut of the species, using models based on the Response Surface Methodology. Design of experiment was defined based on the physiology and culture conditions of the species, and in vitro assays were performed in a two-phase (stomach ad intestine) digestion process, using the species-specific enzyme extract. According to results, intestinal phase of digestion makes the major contribution to the total protein hydrolysis, being the efficiency of the process directly correlated to all the three studied factors. In contrast, the efficiency of carbohydrate hydrolysis was directly correlated to the amount of substrate and inversely to the pH, while reaction time did not exert a significant effect. The physiological range of the factors studied in the assays favoured the hydrolysis of proteins over carbohydrates, a similar scenario to that observed in the live fish. Results from the mathematical models and their simultaneous optimization obtained from this work may have practical applications in design of feeds for this species. [ABSTRACT FROM AUTHOR]

Unique amongst the teleost, Plotosidae catfish possess a dendritic organ (DO) as a purported salt secreting organ, whereas other marine teleosts rely on their gill ionocytes for active NaCl excretion. To address the role of the DO in ionregulation, ligation experiments were conducted in brackish water (BW) 3‰ and seawater (SW) 34‰ acclimated Plotosus lineatus and compared to sham operated fish. Ligation in SW resulted in an osmoregulatory impairment in blood (elevated ions and hematocrit) and muscle (dehydration). However, SW ligation did not elicit compensatory changes in gill or kidney Na+/K+-ATPase (NKA) activity and/or protein expression while a decrease in anterior intestine and increased in posterior intestine were observed but this was not reflected at the protein level. Following ligation in SW, protein levels of carbonic anhydrase (CA) and V-ATPase B subunit (VHAB) were higher in kidney but either lower (CA) or unchanged (VHAB) in other tissues. Taken together, the osmotic disturbance in ligated SW fish indicates the central role of the DO in salt secretion and the absence of a compensatory response from the gill. [ABSTRACT FROM AUTHOR]

The 2010 Deepwater Horizon oil spill coincided with the spawning season of many pelagic fish species in the Gulf of Mexico. Yet, few studies have investigated physiological responses of larval fish to interactions between anthropogenic crude oil exposure and natural factors (e.g. temperature, oxygen levels). Consequently, mahi mahi (Coryphaena hippurus) embryos were exposed for 24 hours to combinations of two temperatures (26 and 30°C) and six concentrations of oiled fractions of weathered oil (from 0 to 44.1 μg ∑50PAHs·L-1). In 56 hours post-fertilization larvae, heart rate, stroke volume and cardiac output were measured as indicators of functional cardiac phenotypes. Fluid accumulation and incidence of edema and hematomas were quantified as indicators of morphological impairments. At both 26 and 30°C, oil-exposed larvae suffered dose-dependent morphological impairments and functional heart failure. Elevation of temperature to 30°C appeared to induce greater physiological responses (bradycardia) at PAH concentrations in the range of 3.0–14.9 μg·L-1. Conversely, elevated temperature in oil-exposed larvae reduced edema severity and hematoma incidence. However, the apparent protective role of warmer temperature does not appear to protect against enhanced mortality. Collectively, our findings show that elevated temperature may slightly decrease larval resilience to concurrent oil exposure. [ABSTRACT FROM AUTHOR]

Deeper reefs are often considered to be less susceptible to local and global disturbances, such as overfishing, pollution and climate change, compared to shallow reefs and therefore could act as refugia for shallow water species. Hence, the interest on deeper reefs has happened at a time when shallow reefs are undergoing unprecedented changes. Here we investigated the hypothesis that fish community differed from shallow to deeper reefs due to factors apart from habitat structure and quality and therefore discuss for the first-time insights of a “deep refuge hypothesis” from Brazilian reefs. We collected data on fish community, benthic community and physiological conditions of two coral species on shallow (< 6 m) and deep reefs (> 25 m). No significant difference on substratum composition was observed comparing sites and depths. Additionally, physiological data on corals also showed similar oxidative status and growth conditions when comparing the two-coral species in shallow and deep reefs. Conversely, our study demonstrated strong differences on reef fish communities in terms of abundance, species richness, trophic groups, size classes and groups of interest when comparing shallow and deeper reefs. Fish abundance was 2-fold higher and species richness was up to 70% higher on deeper reefs. Also, a significant difference was observed comparing trophic groups of reef fish. Macrocarnivore, Mobile invertebrate feeders, Planktivores, Sessile Invertebrates Feeders and Roving Herbivores were more abundant on deeper reefs. On the other hand, Territorialist Herbivores almost exclusively dominated shallow reefs. Strong differences were also observed comparing the abundance of reef fish groups of interest and their respective size classes between shallow and deeper reefs. Ornamental, Great Herbivores and Groupers showed clear differences, with higher abundances being observed in deeper reefs. Considering size classes, larger individuals (> 15 cm) of Great Herbivores, Groupers and Snapper were uniquely recorded at deeper reefs. Additionally, individuals with > 30 cm were recorded almost exclusively on deeper reefs for all the analyzed groups of interest. Our findings suggest that fishing pressure on the target species may be attenuated on deeper reefs, and these regions may therefore be considered as areas of refuge from shallow water impacts. Therefore, the likely potential for deeper reefs protect species from natural or anthropogenic disturbances increases the attention of marine conservation planning and resource management on including deeper reefs in protected areas. [ABSTRACT FROM AUTHOR]

We sought to describe sounds of some of the common fishes suspected of producing unidentified air movement sounds in soundscape surveys of freshwater habitats in the New England region of North America. Soniferous behavior of target fishes was monitored in real time in the field in both natural and semi-natural environments by coupling Passive Acoustic Monitoring (PAM) with direct visual observation from shore and underwater video recording. Sounds produced by five species including, alewife (Alosa pseudoharengus, Clupeidae), white sucker (Catastomus commersonii, Catostomidae), brook trout (Salvelinus fontinalis, Salmonidae), brown trout (Salmo trutta, Salmonidae), and rainbow trout (Oncorhynchus mykiss, Salmonidae) were validated and described in detail for the first time. In addition, field recordings of sounds produced by an unidentified salmonid were provisionally attributed to Atlantic salmon (Salmo salar, Salmonidae). Sounds produced by all species are of the air movement type and appear to be species specific. Our data based on fishes in three distinct orders suggest the phenomenon may be more ecologically important than previously thought. Even if entirely incidental, air movement sounds appear to be uniquely identifiable to species and, hence, hold promise for PAM applications in freshwater and marine habitats. [ABSTRACT FROM AUTHOR]

Nile tilapia (Oreochromis niloticus) is the world’s most widely cultured fish species. Therefore, its nutritional physiology is of great interest from an aquaculture perspective. Studies conducted on several fish species, including tilapia, demonstrated the beneficial effects of dietary salt supplementation on growth; however, the mechanism behind these beneficial effects is still not fully understood. The fish intestine is a complex system, with functions, such as nutrient absorption, ion equilibrium and acid-base balance that are tightly linked and dependent on each other's activities and products. Ions are the driving force in the absorption of feed components through pumps, transporters and protein channels. In this study, we examined the impact of 5% increase in dietary NaCl on protein, lipid, ash and dry matter digestibility, as well as on the expression of intestinal peptide transporters (PepTs) and ion pumps (Na+/K+-ATPase, V-H+-ATPase, N+/H+-Exchanger) in Nile tilapia. In addition, effects on the gut microbiome were evaluated. Our results show that dietary salt supplementation significantly increased digestibility of all measured nutritional components, peptide transporters expression and ion pumps activity. Moreover, changes in the gut microbial diversity were observed, and were associated with lipid digestibility and Na+/K+-ATPase expression. [ABSTRACT FROM AUTHOR]

Aflatoxins (AF) can be cumulative in fish tissues and can influence weight, length, feed intake and survival depending on the species. The aim of this work is to measure performance and aflatoxin levels in tissues of matrinxã (Brycon cephalus) fish chronically exposed to aflatoxin. Aflatoxin was incorporated into fish diets at the following levels: Control Feed + 0 μg AFB1 kg-1; A. Feed + 10 μg AFB1 kg-1; B. Feed + 20 μg AFB1 kg-1; C. Feed + 50 μg AFB1 kg-1. It was used one tank per treatment, each one with 150 juvenile fish, and three replicates within each tank were used for sampling, that was carried out monthly over a period of six months. Aflatoxin was quantified by HPLC in fish liver and muscle after clean up using immunoaffinity columns. Performance was evaluated by using weight, length, consumption and survival rate. Muscle and liver aflatoxin levels were below the limit of detection in all control samples. Aflatoxins B2, G1 and G2 were not detected in any tissues. Traces (values between limits of detection and quantification) of AFB1 were observed in liver tissue in treatment A from day 30 through 90, reaching 0.32 μg AFB1 kg-1 at 150 days of exposure. Treatment B presented traces up to day 60 and had, with a maximum level of 0.39 μg AFB1 kg-1 at 150 days of exposure. Treatment C had aflatoxin residues after day 30, with values ranging from 0.17 to 0.61 μg AFB1 kg-1 during exposure. Muscle samples only had traces of AFB1 in all treatments. Fish was affected by exposure to AFB1 with higher values (P<0.05) for weight and length in treatments A, B and C relative to controls. Therefore, results indicate that matrinxã do not accumulate AFB1 residues in edible tissues, but chronic exposure affects the species. [ABSTRACT FROM AUTHOR]

We evaluated the chemical coding of the myenteric plexus in the proximal and distal intestine of gilthead sea bream (Sparus aurata), which represents one of the most farmed fish in the Mediterranean area. The presence of nitric oxide (NO), acetylcholine (ACh), serotonin (5-HT), calcitonin-gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP) containing neurons, was investigated in intestinal whole mount preparations of the longitudinal muscle with attached the myenteric plexus (LMMP) by means of immunohistochemical fluorescence staining. The main excitatory and inhibitory neurochemicals identified in intestinal smooth muscle were ACh, SP, 5HT, and NO, VIP, CGRP. Some neurons displayed morphological features of ascending and descending interneurons and of putative sensory neurons. The expression of these pathways in the two intestinal regions is largely superimposable, although some differences emerged, which may be relevant to the morphological properties of each region. The most important variances are the higher neuronal density and soma size in the proximal intestine, which may depend on the volume of the target tissue. Since in the fish gut the submucosal plexus is less developed, myenteric neurons substantially innervate also the submucosal and epithelial layers, which display a major thickness and surface in the proximal intestine. In addition, myenteric neurons containing ACh and SP, which mainly represent excitatory motor neurons and interneurons innervating the smooth muscle were more numerous in the distal intestine, possibly to sustain motility in the thicker smooth muscle coat. Overall, this study expands our knowledge of the intrinsic innervation that regulates intestinal secretion, absorption and motility in gilthead sea bream and provides useful background information for rational design of functional feeds aimed at improving fish gut health. [ABSTRACT FROM AUTHOR]

Despite the advance of knowledge about the factors and potential mechanisms triggering the ichthyotoxicity in microalgae, these remain unclear or are controversial for several species (e.g. Heterosigma). Neither typical toxicity tests carried out with cell extracts nor direct exposure to harmful species were proved suitable to unravel the mechanism of harm. Ichthyotoxic species show a complex harmful effect on fish, which is mediated through various mechanisms depending on the species. In this work, we present a method to study sub-lethal effects triggered by reactive oxygen species of a population of harmful algae in vivo over a fish cell line. To that end, Transwell co-cultures in which causative and target species are separated by a 0.4 μm pore membrane were carried out. This allowed the evaluation of the effect of the released molecules by cells in a rapid and compact test. In our method, the harmful effect was sensed through the transcriptional activation of sub-lethal marker Hsp70b in the CHSE214 salmon cell line. The method was tested with the raphidophyte Heterosigma akashiwo and Dunaliella tertiolecta (as negative control). It was shown that superoxide intracellular content and its release are not linked in these species. The methodology allowed proving that reactive oxygen species produced by H. akashiwo are able to induce the transcriptional activation of sub-lethal marker Hsp70b. However, neither loss of viability nor apoptosis was observed in CHSE214 salmon cell line except when exposed to direct contact with the raphidophyte cells (or their extract). Consequently, ROS was not concluded to be the main cause of ichthyotoxicity in H. akashiwo. [ABSTRACT FROM AUTHOR]

Knowledge about the spatial patterns and movements of crustaceans has gained importance since the creation of marine protected areas and the development of spatial management for benthic ecosystems. The Juan Fernández spiny lobster (Jasus frontalis) is an endemic marine species and most valuable resource that exhibits migratory dynamics in a highly spatially regulated fishery. To study movement patterns around Alexander Selkirk Island, a mark-recapture program was implemented in 2008, when approximately 7000 non-commercial (undersized) lobsters were tagged and followed for nearly 14 months. Using quantitative georeferenced data, this study revealed spatial structuring of Juan Fernández spiny lobster and tested hypotheses about alongshore and inshore-offshore movements. Eight clusters were identified around Alexander Selkirk Island, with moderate time-varying connectivity between them. Seasonal inshore-offshore movements were detected all around the island, but more conspicuously to the north. Average travelling distance was 1.2 km (1.7 sd). Our results confirmed that towards the end of austral spring males and females embark in a seasonal offshore migration to deeper waters, returning to shallower waters only during winter. These findings quantitatively consolidate the conceptual migratory model that local fishermen had already inferred for this resource from about a century of sustainable fishing. [ABSTRACT FROM AUTHOR]