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Physiological and morphological acclimation capacities of black‐chinned tilapia, Sarotherodon melanotheron were studied from fish to gill cell level when fish are maintained in freshwater, seawater, and hypersaline conditions. Fish osmoregulatory capacity, gill ionocyte morphology, osmo‐respiratory compromise, O2 consumption rate, branchial antioxidative defense, and cell apoptosis were considered. Captive juvenile tilapias were maintained in controlled freshwater conditions (FW: 0.4 ppt; 12 mOsm kg−1) or gradually transferred to seawater (SW: 32 ppt; 958 mOsm kg−1) and concentrated SW (cSW: 65 ppt; 1920 mOsm kg−1). After 15 days in these conditions, blood osmolality and chloride ion concentration were determined. Gill ionocyte density and morphology were measured using immunolabelled histological sections to specifically detect the sodium pump (NKA). Gill osmo‐respiratory compromise was also calculated along with oxygen consumption rates from normoxic to hypoxic conditions from excised gills (indirect respirometry). Finally, catalase and caspase 3/7activities were recorded from gill extracts. Results indicate that elevated salinity induces an osmotic imbalance and a profound morphological change with proliferating and hypertrophied ionocytes. This thickening of the gill interlamellar cell mass and the shortening of the lamellae induce a reduced osmo‐respiratory ratio and reduced respiratory capacity under both normoxic and hypoxic conditions. Although salinity changes do not affect one of the major antioxidative defense mechanism, it strongly affects apoptosis that appears the most elevated in SW. However, in freshwater condition, fish can maintain their osmotic balance with a low ionocyte density, a low apoptotic level and a drastically reduced O2 consumption in normoxic condition that is maintained in hypoxia. Therefore, S. melanotheron presents the typical functional remodeling due to environmental salinity changes ranging from FW to SW. However, elevated seawater induces major cellular stress inducing a profound gill morphofunctional dysfunctioning. While cell apoptosis is reduced, ionocyte proliferation is massively increased with impaired osmotic regulation and reduced O2 consumption both in normoxic and hypoxic conditions. [ABSTRACT FROM AUTHOR]

Reproduction is one of the most crucial physiological processes for the continuation of the generation of any species. Teleost are one of the most divergent aquatic species. The reproductive neuro-endocrine regulatory studies are limited to only few species. Neuroendocrine regulation is a finely tuned complex mechanistic pathways, involving mainly hypothalamic-pituitary-gonad (HPG) axis. Within the HPG axis, gonadotropin-releasing hormone (GnRH) modulates the synthesis and release of pituitary gonadotropins, which act on the gonads to stimulate steroidogenesis and gametogenesis. Very recently, several novel neuropeptides, associated with reproductive regulation, have been identified. Spexin (SPX), a novel neuropeptide coevolved with the galanin/kisspeptin family, has been identified as a regulator of the species-specific reproductive processes in teleost. Pituitary adenylate cyclase-activating polypeptide (PACAP) is another novel member of the secretin-glucagon peptide family that functions as a hypophysiotropic factor involved in regulating pituitary hormone secretion in fish. These two emerging neuropeptides have pleiotropic functions, but information regarding their exact roles in fish reproduction is very limited. An updated overview of the mechanistic reproductive functions of these two new neuropeptides are highlighted in this review. [ABSTRACT FROM AUTHOR]

Targeted metabolomic analysis was conducted on juvenile Chinook salmon exposed for 10 days to wastewater effluent (WWE) from a large urban treatment plant. Exposures included five dilutions of WWE (20%, 5.3%, 1.4%, 0.4%, and 0.1%) and a control with 7 replicates per treatment. Liver was extracted from fish and analyzed via liquid chromatography - mass spectrometry (LC-MS) for 361 endogenous metabolites, of which 185 were detected. Control-versus-treatment comparisons identified several metabolites that were associated with altered biochemical pathways observed for all treatments, including several that are important for energy generation and utilization. These altered pathways are crucial for fish health and may be an early indicator of potential adverse effects on growth, reproduction, behavior, and immune function. Juvenile ocean-type Chinook salmon spend several days to weeks in the nearshore estuary where they may encounter high concentrations of WWE contaminants. They are exposed to a wide range of potent pharmaceuticals, personal care products, and industrial compounds from WWE that have the potential to affect physiological homeostasis and disrupt their normal life cycle. [ABSTRACT FROM AUTHOR]

Wastewater treatment plants release complex mixtures of chemicals into the aquatic environment as wastewater effluent (WWE); however, the effects of these mixtures are still poorly understood. Chinook salmon (Oncorhynchus tshawytscha) are a culturally important species in the Pacific Northwest and are a vital food resource for southern resident killer whales (Orcinus orca) that are listed as 'critically endangered' under the U.S. Endangered Species Act (ESA). Chinook populations have declined drastically in this region and have failed to show significant recovery despite regional-to-federal efforts, resulting in many populations being listed as threatened under the ESA. One source of stress to juvenile Chinook is chemical pollution from WWE during their outmigration along river corridors and residency in estuaries. In this study, we investigated effects of WWE on juvenile Chinook health in a ten-day exposure to dilutions of WWE from 0.1% to 20%. At the end of the exposure, we measured endpoints associated with endocrine disruption, brain function, osmoregulation, stress, and metabolism. Exposure to WWE significantly (a = 0.1 for all analyses) induced vitellogenesis, indicating endocrine system disruption. We saw significant reductions in plasma glucose, an indication of stress, and brain Na+/K+-ATPase (NKA) activity, an enzyme essential for neuronal signaling. Lastly, metabolism was affected as evidenced by altered total protein, cholesterol, and albumin in plasma, a drastic decrease in whole body lipid content, and a significant increase in visible liver anomalies. We compared contaminant concentrations in exposure water with effects concentrations from the literature for chemicals known to induce vitellogenin or inhibit brain NKA. For most contaminants, concentrations in exposure waters were several orders of magnitude below effects concentrations in the literature. The exception was estrogenic hormones, which were detected at similar concentrations in this study compared to concentrations in other studies that induced vitellogenin. Based on comparisons to the literature, contaminants measured in this study could not explain the inhibition of brain NKA; however, WWE mixtures contain many quantified and undetected compounds that are likely acting together to cause harmful effects in Chinook. This research highlights the need for improved wastewater treatment to improve aquatic health and mitigate effects to threatened species like Puget Sound Chinook salmon. [ABSTRACT FROM AUTHOR]

Striped wallago catfish (Wallago leerii), a freshwater catfish species with high economic value, has been extensively exploited in Indonesia. Therefore, domestication is necessary to ensure the sustainability of this species through a hormonal approach. This research aimed to evaluate hormonal treatments on the bioreproductive and physiological parameters of broodstocks during domestication. Collected broodstocks from Kampar River, Indonesia, were adapted in semiconcrete ponds and fed daily with live tilapia (Oreochromis niloticus) and bonylip barb (Osteochilus vittatus) fingerlings at a rate of 5% weight of biomass per day. Selected broodstocks (length:55.59 ± 5.21 cm; weight:1.60 ± 0.53 kg) were randomly divided into three experimental grdoups with four replicates each. Each group was injected with human chorionic gonadotropin (HCG), Spawnprime™, and Ovaprim™ hormones (0.1 mL/kg body weight). Egg sizes, fecundity, fertility rate, hatching rate, embryo development, and estradiol, glucose, hemoglobin, and cortisol levels were analyzed. HCG and Ovaprim™ treatment led to significant improvements in egg diameter compared to Spawnprime™ (p < 0.05). This finding was supported by an increase in estradiol levels (p < 0.05). However, HCG and Ovaprim™ did not reach optimal performance, as shown by the low fertility rates (9.83–12.33%), hatching rates (24.06–34.17%), and larval abnormalities. Hormone injection did not significantly impact the glucose level for all treatments (p > 0.05). On the other hand, hemoglobin was significantly lower in the HCG- and Ovaprim-treated broodstocks at the end of the experiment (p < 0.05), while the other treatments did not show significant differences (p > 0.05). Significant differences in cortisol levels were identified in all treatments (p < 0.05), except for the HCG-treated broodstocks (p > 0.05). In conclusion, HCG and Ovaprim™ improved striped wallago catfish gonadal maturation up to artificial spawning, whereas Spawnprime™ had a weak effect. The usage of hormones on gonadal maturation impacted some of their physiological parameters. [ABSTRACT FROM AUTHOR]

The United Nations World Drug Report published in 2022 alarmed that the global market of illicit drugs is steadily expanding in space and scale. Substances of abuse are usually perceived in the light of threats to human health and public security, while the environmental aspects of their use and subsequent emissions usually remain less explored. However, as with other human activities, drug production, trade, and consumption of drugs may leave their environmental mark. Therefore, this paper aims to review the occurrence of illicit drugs in surface waters and their bioaccumulation and toxicity in fish. Illicit drugs of different groups, i.e., psychostimulants (methamphetamines/amphetamines, cocaine, and its metabolite benzoylecgonine) and depressants (opioids: morphine, heroin, methadone, fentanyl), can reach the aquatic environment through wastewater discharge as they are often not entirely removed during wastewater treatment processes, resulting in their subsequent circulation in nanomolar concentrations, potentially affecting aquatic biota, including fish. Exposure to such xenobiotics can induce oxidative stress and dysfunction to mitochondrial and lysosomal function, distort locomotion activity by regulating the dopaminergic and glutamatergic systems, increase the predation risk, instigate neurological disorders, disbalance neurotransmission, and produce histopathological alterations in the brain and liver tissues, similar to those described in mammals. Hence, this drugs-related multidimensional harm to fish should be thoroughly investigated in line with environmental protection policies before it is too late. At the same time, selected fish species (e.g., Danio rerio, zebrafish) can be employed as models to study toxic and binge-like effects of psychoactive, illicit compounds. [ABSTRACT FROM AUTHOR]

Immune nutrition is currently used to enhance fish health by incorporating functional ingredients into aquafeeds. This study aimed to investigate the connections between tryptophan nutrition and the network that regulates the communication pathways between neuroendocrine and immune systems in European seabass (Dicentrarchus labrax). When tryptophan was supplemented in the diet of unstressed fish, it induced changes in the hypothalamic-pituitary-interrenal axis response to stress. Tryptophan-mediated effects were observed in the expression of anti-inflammatory cytokines and glucocorticoid receptors. Tryptophan supplementation decreased pro-opiomelanocortin b-like levels, that are related with adrenocorticotropic hormone and cortisol secretion. When stressed fish fed a tryptophan-supplemented diet were subjected to an inflammatory stimulus, plasma cortisol levels decreased and the expression of genes involved in the neuroendocrine response was altered. Modulatory effects of tryptophan dietary intervention on molecular patterns seem to be mediated by altered patterns in serotonergic activity. [ABSTRACT FROM AUTHOR]

The nutritional quality of food can affect the health of animals. This study examined the effects of dietary supplementation with Lippia sidoides essential oil (LSEO) on the physiology of Danio rerio. Four hundred fourty‐eight fish were divided into 28 tanks and subjected to different dietary treatments: a control group with no supplementation, a group with grain alcohol supplementation and five groups with LSEO at concentrations of 0.25%, 0.50%, 0.75%, 1.00% and 1.25%. After 15 days, histological and enzymatic analyses were conducted. The 0.25% LSEO group exhibited lower glutathione peroxidase and catalase activity compared to the 1.00% group. Additionally, fish in the 0.25% LSEO group showed improved liver, kidney and splenic integrity indices. These findings support the inclusion of 0.25% LSEO in the diet of D. rerio, suggesting potential benefits for fish physiology and encouraging further research on phytotherapeutics in fish diets. [ABSTRACT FROM AUTHOR]

Simple Summary: Aquaculture produces fish that are then marketed to the population, but the type of production used today generates stress in fish. Constant stress, which occurs through the hormone cortisol, negatively affects the seawater adaptation of juvenile fish, which is detrimental to the aquaculture process. For many years, it was thought that only cortisol influenced physiological responses in fish. However, in recent years, the cortisol intermediary 11-deoxycorticosterone (DOC) has been considered a complementary stress-related hormone in fish. Given the above, this work aims to unravel whether DOC is involved in the regulation of early physiological and transcriptional responses in fish gills. To ascertain this, juvenile rainbow trout were injected with DOC and/or pharmacological inhibitors of corticosteroid receptors. Then, the physiological parameters and RNA sequencing of the gills were analyzed. The experiment concluded that DOC is important during stress and that it is vital for the balance between minerals and water in fish. The results of this work will help us understand the other effects of DOC in fish, as well as help improve the monitoring of animal welfare in the aquaculture industry through the incorporation of novel and potential stress molecular biomarkers. In aquaculture, stress can negatively affect fish growth. For years, the cortisol hormone has been thought to play both glucocorticoid and mineralocorticoid functions. Nevertheless, recent research has suggested that 11-deoxycorticosterone (DOC) released during stress could contribute to cortisol actions, though this process is still misunderstood. Here, we evaluated the DOC effects on physiological and early transcriptional responses by RNA-seq. Juvenile rainbow trout were treated with DOC and/or glucocorticoids (mifepristone) or mineralocorticoid (eplerenone) receptor antagonists. Subsequently, plasma was collected, and cDNA libraries were generated from the gills of vehicle (control), DOC, mifepristone, mifepristone with DOC, eplerenone, and eplerenone with DOC groups. Calcium and phosphate levels in plasma were changed. Results revealed 914 differentially expressed transcripts (DETs) induced by DOC compared with control, mainly associated with sodium ion transmembrane transport, gluconeogenesis, negative regulation of transmembrane transport, and activation of innate immune response. DOC versus eplerenone with DOC comparison displayed 444 DETs related to cell-cell junction organization, canonical glycolysis, positive regulation of immune response, and potassium ion transport. Conversely, no DETs were detected in DOC versus mifepristone with DOC comparison. These data suggest that DOC has a relevant role in gill stress response and ion transport, which is differentially regulated by mineralocorticoid receptors. [ABSTRACT FROM AUTHOR]

Climate-driven species redistributions are facilitated by niche modifications that increase a species's chances of establishment in novel communities. It is well understood how range-extending species adjust individual niche traits when entering novel environments, yet whether modification of ecological niche traits collectively alters the pace of range extensions or contractions remains unknown. We quantified habitat niche, abundance, physiological performance and cellular defence/damage of range-extending coral reef fishes and coexisting local temperate fishes along a 2000 km latitudinal gradient. We also assessed their dietary and behavioural niches, and establishment potential, to understand whether ecological generalism facilitates successful range extension of coral reef fishes. The coral reef fish that increased all ecological niches, showed stronger establishment, increased physiological performance and cellular damage, but decreased cellular defence at their cold-range edge, whereas tropical species that showed unmodified ecological niches showed lower establishment. One temperate species showed decreased abundance, habitat niche width and body condition, but increased cellular defence, cellular damage and energy reserves at their warm-trailing range, while other temperate species showed contrasting responses. Therefore, ecological generalists might be more successful than ecological specialists during the initial stages of climate change, with increasing future warming strengthening this pattern by physiologically benefitting tropical generalists but disadvantaging temperate specialists. [ABSTRACT FROM AUTHOR]

The current research work provided insights into the expression patterns of key genes in the BPG axis of Mugil cephalus females, highlighting differences between wild and captive environments during the spawning season. The investigated genes include Kiss2, Gpr54, Gnrh1, and Drd2 in the brain and ovary, as well as Lhβ, Fshβ, and Slα in the pituitary and ovary. The finding indicated that the relative expression of all examined genes is elevated in mature females compared to immature ones across all examined tissues (brain, pituitary, and ovary). The observation that the expressions of the examined genes in wild females of M. cephalus are highly correlated, either directly or inversely, with their counterparts in captive females, indicated a connection between gene expression patterns and the different environments (wild vs. captive). The results between wild and captive females were in significant values (P≤ 0.05). Overall, the observed correlations and significant differences in gene expression proposed potential impacts of captivity on the reproductive physiology of these fish. [ABSTRACT FROM AUTHOR]

This research introduces an optimal Fin Ray gripper design for vegetable handling in horticulture applications. Fin Ray grippers are triangular with crossbeams. The gripper flexes and adjusts to the structure of the object upon activation. The change in the gripper's form resembles fish fin physiology. This research entails the design and fabrication of Fin Ray inclined grippers with variations in their geometrical structure, namely, the gap between the crossbeams, the inclination angle of the crossbeams, and the thickness of the crossbeams. The Box-Behnken design and analysis of variance approaches were used to assess the major impacts, interactions, and importance of the crossbeam's characteristics on weightlifting capacity and displacement. The Fin Ray gripper design parameters were successfully optimised by the chosen Response Surface Methodology. Less force is needed to obtain a good grasp on an object when a design is made to achieve optimum weightlifting capacity and bending displacement. The gripper's design and analysis, as well as the experimental results demonstrating how well it handles various types of vegetables, are described in the paper. The design of an optimal Fin Ray gripper presents a new and unique idea for adaptive grasping in horticultural robots. [ABSTRACT FROM AUTHOR]

Simple Summary: The sustainability of aquaculture's growth is a worldwide challenge in the coming decades. Among the different approaches considered (e.g., implementation of recirculation systems, zero waste, etc.), reducing the use of raw materials imported from third countries might help to lower the carbon footprint of European aquaculture. Soybean meal (SBM) is one of the most widely used alternative raw materials to replace fishmeal, but is largely imported from Argentina, Brazil, and/or USA. Red vetchling (Lathyrus cicera) is a crop locally produced in Europe that might reduce the European dependency on SBM imports. Here, the replacement of SBM with red vetchling in diets for rainbow trout (Oncorhynchus mykiss) juveniles has been evaluated in different percentages (from 0 to 100%). Only fish fed a diet where SBM has been replaced at 100% showed lower growth, an altered amino acid profile in fish fillet, and some histopathological signs in the liver (greater % of pyknotic nuclei). Also, although temporally, glucose and triglycerides blood plasma levels were reduced, normal values were found at 24 h after feeding. Since vetchling meal can partially replace SBM without a negative effect on fish growth or physiology, its use might allow the reduction of SBM imports and the carbon footprint of European aquaculture. In fish diets, soybean meal (SBM) is still positioned as the most widely used alternative to replace fishmeal. Red vetchling (Lathyrus cicera), a crop locally produced in Europe, is here evaluated as a substitute for SBM. Rainbow trout (Oncorhynchus mykiss) juveniles (10.34 ± 0.04 g) were fed for 90 days. Six experimental diets replacing the SBM content at 0, 8, 16, 33, 66, and 100% (Named Control, T8, T16, T33, T66, and T100) were tested. Growth performance and fish fillet amino acid composition were only significantly reduced in fish fed the T100 diet. Histopathological analysis showed that no major alterations were observed in the intestine, while T100 fish had a higher density of pyknotic nuclei in the hepatocytes than the Control, but similar hepatocyte surface coverage. Finally, postprandial levels of glucose and triglycerides in blood plasma decreased when red vetchling content was increased, but was only not fully restored after 24 h in the case of glucose in T66 and T100 fish. According to these results, red vetchling meal can replace up to 66% of the SBM without a negative effect on fish growth or physiology, representing a good alternative raw material for reducing European aquaculture's dependency on SBM imports and the carbon footprint of aquafeeds. [ABSTRACT FROM AUTHOR]

Analyzing digestive enzyme concentration in the gut is important to know about the digestive physiology of fish. Therefore, we determined concentrations of protease, lipase, and amylase enzyme in gut extracts of juvenile and adult groups of Notopterus notopterus relative to total body length (TBL), body weight (W), gut length (GL), relative gut length (RGL), Zihler's index (ZI) and condition factor (K). A total of 60 N. notopterus specimens (30 juvenile and 30 adult) were collected, the gut of each removed, homogenized, and evaluated for the concentrations of protease, lipase, and amylase. Protease and lipase concentration were observed significantly (P < 0.01) correlated with increased TBL, W, and GL in both juvenile and adult groups of N. notopterus. Amylase concentration significantly (P < 0.01) increases with an increase in TBL, weight, and GL in the juvenile group, whereas amylase concentration significantly (P < 0.01) decreases with an increase in TBL, W, and GL in the adult group. K had a significant (P < 0.01) positive correlation with protease and lipase concentrations in both juvenile and adult groups, whereas K showed a significant (P < 0.01) positive correlation with amylase concentrations in juvenile and significant (P < 0.01) negative correlation in the adult group. Protease and lipase concentration were observed significantly (P < 0.01) correlated with an increase in ZI in the juvenile and adult groups. Amylase concentration significantly (P < 0.01) increases with an increase in ZI in the juvenile group, whereas amylase concentration significantly (P < 0.01) decreases with an increase in ZI in the adult group. The concentrations of protease (344.12 U/mg) and lipase (172.49 U/mg) were observed high in juvenile and adult groups, whereas amylase concentration (3.80 U/mg) was found low in the juvenile and adult N. notopterus groups. Present study results revealed the digestive physiology and carnivorous behavior of N. notopterus. Moreover, information from the present study about digestive enzyme concentration in juvenile and adult species of N. notopterus provides valuable information to understand the digestive physiology of carnivorous fishes. [ABSTRACT FROM AUTHOR]

The effects of increased levels of carbon dioxide (CO2) on the Earth's temperature have been known since the end of the 19th century. It was long believed that the oceans' buffering capacity would counteract any effects of dissolved CO2 in marine environments, but during recent decades, many studies have reported detrimental effects of ocean acidification on aquatic organisms. The most prominent effects can be found within the field of behavioural ecology, e.g., complete reversal of predator avoidance behaviour in CO2‐exposed coral reef fish. Some of the studies have been very influential, receiving hundreds of citations over recent years. The results have also been conveyed to policymakers and publicized in prominent media outlets for the general public. Those extreme effects of ocean acidification on fish behaviour have, however, spurred controversy, given that more than a century of research suggests that there are few or no negative effects of elevated CO2 on fish physiology. This is due to sophisticated acid–base regulatory mechanisms that should enable their resilience to near‐future increases in CO2. In addition, an extreme "decline effect" has recently been shown in the literature regarding ocean acidification and fish behaviour, and independent research groups have been unable to replicate some of the most profound effects. Here, the author presents a brief historical overview on the effects of elevated CO2 and ocean acidification on fishes. This historical recap is warranted because earlier work, prior to a recent (c. 10 year) explosion in interest, is often overlooked in today's ocean acidification studies, despite its value to the field. Based on the historical data and the current knowledge status, the author suggests future strategies with the aim to improve research rigour and clarify the understanding of the effects of ocean acidification on fishes. [ABSTRACT FROM AUTHOR]

Protein turnover is highly energy consuming and overall relates to an organism's growth performance varying largely between species, e.g., due to pre-adaptation to environmental characteristics such as temperature. Here, we determined protein synthesis rates and capacity of protein degradation in white muscle of the cold stenothermal Antarctic eelpout (Pachycara brachycephalum) and its closely related temperate counterpart, the eurythermal common eelpout (Zoarces viviparus). Both species were exposed to acute warming (P. brachycephalum, 0 °C + 2 °C day−1; Z. viviparus, 4 °C + 3 °C day−1). The in vivo protein synthesis rate (Ks) was monitored after injection of 13C-phenylalanine, and protein degradation capacity was quantified by measuring the activity of cathepsin D in vitro. Untargeted metabolic profiling by nuclear magnetic resonance (NMR) spectroscopy was used to identify the metabolic processes involved. Independent of temperature, the protein synthesis rate was higher in P. brachycephalum (Ks = 0.38–0.614 % day−1) than in Z. viviparus (Ks= 0.148–0.379% day−1). Whereas protein synthesis remained unaffected by temperature in the Antarctic species, protein synthesis in Z. viviparus increased to near the thermal optimum (16 °C) and tended to fall at higher temperatures. Most strikingly, capacities for protein degradation were about ten times higher in the Antarctic compared to the temperate species. These differences are mirrored in the metabolic profiles, with significantly higher levels of complex and essential amino acids in the free cytosolic pool of the Antarctic congener. Together, the results clearly indicate a highly cold-compensated protein turnover in the Antarctic eelpout compared to its temperate confamilial. Constant versus variable environments are mirrored in rigid versus plastic functional responses of the protein synthesis machinery. [ABSTRACT FROM AUTHOR]

Beta-glucans have immense potential to stimulate immune modulation in fish by being injected intramuscularly, supplemented with feed or immersion routes of administration. We studied how supplementing Labeo rohita's diet with reishi mushroom powder containing beta-glucan influenced immunological function. A supplemented diet containing 10% reishi mushroom powder was administered for 120 days. Afterwards, analyses were conducted on different immunological parameters such as antioxidants, respiratory burst, reactive oxygen species (ROS), alternative complement activity, and serum immunoglobulin, which resulted significant increases (p < 0.05; p < 0.01) for the reishi mushroom-fed immune primed L. rohita. Additionally, analyzing various hematological parameters such as erythrocytes and leukocytes count were assessed to elucidate the immunomodulatory effects, indicating positive effects of dietary reishi mushroom powder on overall fish health. Furthermore, the bacterial challenge-test with 1.92 × 104 CFU/ml intramuscular dose of Aeromonas veronii showed enhanced disease-defending system as total serum protein and lysozyme activity levels accelerated significantly (p < 0.01). Nevertheless, reishi mushroom powder contained with beta-glucan ameliorated the stress indicating parameters like acetylcholinesterase (AChE), serum-glutamic pyruvic transaminase (SGPT) and serum-glutamic oxaloacetic transaminase (SGOT) enzyme activities results suggested the fish's physiology was unaffected. Therefore, the results indicated that adding dietary reishi mushroom as a source of beta-glucan could significantly boost the immune responses in Rohu. [ABSTRACT FROM AUTHOR]

Fish health can influence important population-level processes, especially those trying to deal with challenges posed by the natural environment, and growth, which in turn affect stock productivity. Two experiments were conducted to evaluate the metabolites of epidermal mucus in response to two threats of environment faced by the fishes: starvation and pathogenic attack; with the aim to check the alteration in values of innate immune parameters in the epidermal mucus of three Indian major carps, Catla catla, Labeo rohita, and Cirrhinus mrigala. Study showed that, in all three species the amount of mucus secretion and parameters like protein, carbohydrate and lipid of skin mucus altered after both the challenge trials and their concentration differed with respect to species. In particular, immune parameters including lysozyme, alkaline phosphatase and protease increased after both challenges (starvation and pathogenic attack) to face the stress. In contrast myeloperoxidase activity decreased significantly (P < 0.05) after the challenge of starvation but its value increased with pathogen challenge. Variations in mucosal parameters thus could be employed as possible non-invasive biomarkers for studying fish physiology in response to environmental stresses and as an integrated approach to assess the particular species response to the specific condition. [ABSTRACT FROM AUTHOR]

Simple Summary: The greater amberjack (Seriola dumerili) is an economically important fish with high farming value. This species is intolerant to hypoxia, which makes it susceptible to mass mortality and hinders the progress of amberjack cultivation. Based on a comparative analysis of the liver transcriptome between acute hypoxia-tolerant (HT) and intolerant (HS) groups, this study first explored the molecular mechanisms of acute hypoxia in greater amberjack. The results showed that the glycolipid metabolism, antioxidant activity, and apoptotic pathways of greater amberjack significantly responded when exposed to acute hypoxia. In addition, the relative downregulation of apoptosis and autophagy-related genes, such as endog, hm13, and casp6, was also detected in the HT group. The NF-kB pathway was partly promoted in the HT group relative to the HS group to resist apoptosis. This investigation will offer significant technical assistance in the prevention of death caused by acute hypoxia and the subsequent reduction in financial losses. Acute hypoxia is a common abiotic stress in commercial aquaculture and has significant effects on fish physiology and metabolism. Due to its large size and rapid growth, the greater amberjack (Seriola dumerili) is an economically important fish with high farming value. This species is intolerant to hypoxia, which makes it susceptible to mass mortality and hinders the progress of amberjack cultivation. Based on a comparative analysis of the liver transcriptome between acute hypoxia-tolerant (HT) and -intolerant (HS) groups, this study first explored the molecular mechanisms of acute hypoxia in greater amberjack. By simulating the acute hypoxic environment and using RNA sequencing (RNA-Seq), the differences in liver transcriptional changes between the acute hypoxia-tolerant (HT) and hypoxia-intolerant (HS) groups of greater amberjack were probed. Based on differential expression analysis, 829 differentially expressed genes (DEGs) were screened in both groups. Relative to the HS group, 374 DEGs were upregulated and 455 were downregulated in the HT group. Compared with the HS group, genes such as slc2a5 and prkaa2 related to promoting sugar transport and inhibiting lipid syntheses were upregulated, while genes that inhibit gluconeogenesis and promote lipid syntheses, such as pgp and aacs, were downregulated. The expression of odc1 was significantly and relatively downregulated in the HT group, which would lead to the inhibition of intracellular antioxidant activity and decreased scavenging of ROS. The NF-kB pathway was also promoted to some extent in individuals in the HT group relative to the HS group to resist apoptosis. In addition, the relative downregulation of apoptosis and autophagy-related genes, such as endog, hm13, and casp6, was also detected in the HT group. The present findings first reported the regulation mechanism by which liver tissue coped with the acute hypoxia stress in greater amberjack, which will provide important technical support for preventing acute hypoxia-induced death in advance and reducing economic losses. [ABSTRACT FROM AUTHOR]

The experiment aimed to evaluate the plasticity of juvenile Russian sturgeon (Acipenser gueldenstaedtii, J. F. Brandt & Ratzeburg, 1833) reared in a floating cage located on a pond. The biological material was 1400 juvenile Russian sturgeon with a mean weight of 9 g/fish and 40 days of age. The intensive rearing system was a 5x5x3 m floating cage in a pond. The fish were fed NUTRA MP-L extruded feed containing 52% crude protein and 20% fat three times a day. The experimental results showed a 64% survival of Russian sturgeon juveniles and the evaluation of productive bioindicators demonstrates high technological plasticity at 50% of the tested group. From the analysis of rearing conditions (environmental and technological), it was concluded that Russian sturgeon juveniles show a certain degree of plasticity depending on the adaptability of the Russian sturgeon to the different environmental conditions which depend principally on the anatomy and physiology of the species Acipenser gueldenstaedtii. [ABSTRACT FROM AUTHOR]

Changes in water temperature and its seasonal timing influences the physiological processes of many aquatic ectotherms. Wastewater treatment plants (WWTP) contribute to warmer and more consistent water temperatures in streams draining the North American Great Plains, particularly during winter months. Reduced variation in seasonal water temperature may adversely affect fishes that rely on temperature fluctuation or specific overwintering temperatures for reproductive cues. We used johnny darter Etheostoma nigrum (Family Percidae), a thermally sensitive species native to the South Platte River Basin, as a focal species to assess the effects of winter water temperature regulations in Colorado.Our objective was to evaluate the effects of winter stream temperature and winter duration on reproductive success of johnny darter in the laboratory to inform development of water quality criteria for the South Platte River Basin. Winter duration (60, 90 or 120 days) and temperature (4 or 12°C) were crossed in a factorial design of six treatments that simulated warmed effluent‐impacted streams as well as streams with a more natural thermal regime. We defined reproductive success in johnny darter by examining four reproductive endpoints: (1) spawning timing, (2) egg and larvae production, (3) egg success, and (4) egg development. Across the four endpoints, seven main response variables were measured: spawning initiation date, eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, egg‐to‐larva survival and days to hatch.Winter temperature and duration influenced spawning timing and egg development. Earlier spawning initiation dates were observed in fish exposed to 12°C winters and was associated with a higher number of days to hatch. Eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, and egg‐to‐larva survival were similar among winter treatments.Although the State of Colorado chronic winter water temperature standard of 12°C appears to be adequate for egg and larvae production in johnny darter, our results showed that fish exposed to the standard began spawning significantly earlier than fish exposed to 4°C winters. Evaluating reproductive output in the context of seasonal timing is valid because spawning timing has the potential to affect overall production and egg development, and consequently recruitment and population sustainability. Therefore, spawning timing should be considered when making management decisions and revising water temperature standards.The warming of streams and rivers from WWTP effluent is a global issue, especially in areas that are undergoing rapid urbanisation. Fishes are particularly sensitive to water temperature and many fishes worldwide are likely to be experiencing changes in important physiological processes, affecting both reproduction and survival. Our study indicates that reproductive timing could be influenced by stream warming and stresses the need for further studies on the influence of anthropogenic effects on stream warming. [ABSTRACT FROM AUTHOR]

Fish skin is the first barrier against external invasion, and also an important interface for communication between males and females during reproduction. Nonetheless, sexual dimorphism in the physiology of fish skins is still poorly understood. Herein, transcriptomes of skin were comparatively analysed between males and females in spinyhead croaker, Collichthys lucidus. Totally, 170 differentially expressed genes (DEG) were detected, including 79 female‐biased genes and 91 male‐biased genes. Gene ontology (GO) annotation items of the DEGs were mainly enriched in biological process items (86.2%), including regulation of biological processes, responses to chemical and biological stimuli, transport and secretion, movement, immune response, tissue development, etc. In KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis, the male‐biased genes were enriched in pathways including those related to immunity such as the TNF signalling pathway and IL‐17 signalling pathway, whereas the female‐biased genes were enriched in pathways including those related to female steroids such as ovarian steroidogenesis and oestrogen signalling pathway. In addition, odf3 was found to be a male‐specific expression gene, being a candidate marker for phenotypic sex. Thus, the sexual difference in gene expression in fish skin in spawning season was uncovered by transcriptome analysis for the first time, providing new insights into sexual dimorphism in the physiology and functions of fish skin. [ABSTRACT FROM AUTHOR]

Simple Summary: To warrant food security and nutrition, more sustainable aquafeeds should be used in fish farming, and the content of fish meal (FM) in fish diets should be reduced. Soybean meal (SBM) is one of the most commonly used alternative raw materials to replace FM in commercial diets, although a high SBM dietary content can affect fish growth, physiology, and wellbeing. Although these effects are known to be produced by several antinutritional factors (ANFs), the underlying mechanisms are still not fully understood. Deeper characterization of how SBM dietary content alters fish physiology will allow the development of more integrative fish physiology monitoring. In the present work, the expression of six microRNAs (miRs) in blood plasma was associated with a high SBM dietary content and related physiological consequences. Circulating miRs can be used as a less invasive procedure to monitor fish physiology without the need of animal sacrifice, allowing the development of more sustainable aquafeeds with the use of fewer animals in experimentation. High dietary SBM content is known to induce important physiological alterations, hampering its use as a major FM alternative. Rainbow trout (Oncorhynchus mykiss) juveniles were fed two experimental diets during 9 weeks: (i) a FM diet containing 12% FM; and (ii) a vegetable meal (VM) diet totally devoid of FM and based on SBM (26%). Fish fed the VM diet did not show reduced growth performance when compared with fish fed the FM diet. Nevertheless, fish fed the VM diet had an increased viscerosomatic index, lower apparent fat digestibility, higher aminopeptidase enzyme activity and number of villi fusions, and lower α-amylase enzyme activity and brush border integrity. Small RNA-Seq analysis identified six miRs (omy-miR-730a-5p, omy-miR-135c-5p, omy-miR-93a-3p, omy-miR-152-5p, omy-miR-133a-5p, and omy-miR-196a-3p) with higher expression in blood plasma from fish fed the VM diet. Bioinformatic prediction of target mRNAs identified several overrepresented biological processes known to be associated with high dietary SBM content (e.g., lipid metabolism, epithelial integrity disruption, and bile acid status). The present research work increases our understanding of how SBM dietary content has a physiological impact in farmed fish and suggests circulating miRs might be suitable, integrative, and less invasive biomarkers in fish. [ABSTRACT FROM AUTHOR]

Background and Aims: Coronavirus disease-2019 (COVID-19) impacts increasing the use of disinfectants (benzalkonium chloride), which indirectly accumulate in water. The disinfectant accumulation in waters has been studied, but there has been no study of its impact on aquatic commodities, especially fish with a high sensitivity, one of which is goldfish (Carassius auratus). Benzalkonium chloride can potentially affect several body proteins, including the cytoskeleton, nervous and endocrine systems, and fish physiology. This study aimed to determine the impact of benzalkonium chloride as a disinfectant on the level of color brightness, growth, gill histopathology, and mortality in goldfish. This investigation provides input into the impact of using disinfectants to prevent COVID-19 on aquatic commodities. Materials and Methods: This study utilized goldfish specimens sourced from Tulungagung, East Java, Indonesia. The experiment involved different concentration levels of benzalkonium chloride: (T1) 0 mg/L, (T2) 0.03 mg/L, (T3) 0.06 mg/L, (T4) 0.09 mg/L, and (T5) 0.12 mg/L. The research data were subjected to an analysis of variance for analysis. In cases where significant differences were observed, Duncan's test was conducted for color brightness, growth, and mortality data. Furthermore, if the gill histopathological data yielded significant differences, additional tests were applied (Kruskal-Wallis and Mann-Whitney test). Results: The findings of this study demonstrated significant differences (p < 0.05) in the level of color brightness, growth, gill histopathology, and mortality in goldfish in response to varying concentrations of benzalkonium chloride. The relationship between the length and weight of the goldfish was analyzed using regression coefficients (b values), which were determined as 4.86, -0.04, -0.2, 0.8, and -0.07, respectively. Notably, the brightness level in the T2 group exhibited positive color results with a hue value of 11.55°, while optimal growth was observed in the T4 group, as evidenced by b value of 0.8. The gill histopathological data showed significant differences (p < 0.05). The scoring of histopathological damage in the goldfish gills ranged from 0 to 10, with higher scores indicating more severe damage. The highest total score of 10 was observed in the T5 group exposed to a concentration of 0.12 mg/L, resulting in an 85% mortality rate. This indicates that benzalkonium chloride, with its toxic compounds, can disrupt the respiratory system of fish and lead to death. Conclusion: The effects of benzalkonium chloride were evident even at a concentration of 0.03 mg/L. With increasing concentration, there was an increase in mortality rate, a decrease in growth, and a rise in histopathological damage to the gills. These findings highlight the negative impact of using conventional disinfectants on water and its organisms, emphasizing the need for further research on environmentally friendly alternatives. [ABSTRACT FROM AUTHOR]

Physiological effects of ocean acidification associated with elevated CO2 concentrations in seawater is the subject of numerous studies in teleost fish. While the short time within-generation impact of ocean acidification (OA) on acid-base exchange and energy metabolism is relatively well described, the effects associated with transgenerational exposure to OA are much less known. Yet, the impacts of OA can vary in time with the potential for acclimation or adaptation of a species. Previous studies in our lab demonstrated that transgenerational exposure to OA had extensive effects on the transcriptome of the olfactory epithelium of European sea bass (Dicentrarchus labrax), especially on genes related to ion balance, energy metabolism, immune system, synaptic plasticity, neuron excitability and wiring. In the present study, we complete the previous work by investigating the effect of transgenerational exposure to OA on the hepatic transcriptome of European sea bass. Differential gene expression analysis was performed by RNAseq technology on RNA extracted from the liver of two groups of 18 months F2 juveniles that had been exposed since spawning to the same AO conditions as their parents (F1) to either actual pH or end-of-century predicted pH levels (IPCC RCP8.5), respectively. Here we show that transgenerational exposure to OA significantly impacts the expression of 236 hepatic transcripts including genes mainly involved in inflammatory/immune responses but also in carbohydrate metabolism and cellular homeostasis. Even if this transcriptomic impact is relatively limited compared to what was shown in the olfactory system, this work confirmed that fish transgenerationally exposed to OA exhibit molecular regulation of processes related to metabolism and inflammation. Also, our data expand the up-regulation of a key gene involved in different physiological pathways including calcium homeostasis (i.e. pthr1), which we already observed in the olfactory epithelium, to the liver. Even if our experimental design does not allow to discriminate direct within F2 generation effects from transgenerational plasticity, these results offer the perspective of more functional analyses to determine the potential physiological impact of OA exposure on fish physiology with ecological relevance. [ABSTRACT FROM AUTHOR]

Cholesterol has been used as additive in fish feeds due to the reduced use of fish meal and fish oil. In order to evaluate the effects of dietary cholesterol supplementation (D-CHO-S) on fish physiology, a liver transcriptome analysis was performed following a feeding experiment on turbot and tiger puffer with different levels of dietary cholesterol. The control diet contained 30% fish meal (0% fish oil) without cholesterol supplementation, while the treatment diet was supplemented with 1.0% cholesterol (CHO-1.0). A total of 722 and 581 differentially expressed genes (DEG) between the dietary groups were observed in turbot and tiger puffer, respectively. These DEG were primarily enriched in signaling pathways related to steroid synthesis and lipid metabolism. In general, D-CHO-S downregulated the steroid synthesis in both turbot and tiger puffer. Msmo1, lss, dhcr24, and nsdhl might play key roles in the steroid synthesis in these two fish species. Gene expressions related to cholesterol transport (npc1l1, abca1, abcg1, abcg2, abcg5, abcg8, abcb11a, and abcb11b) in the liver and intestine were also extensively investigated by qRT-PCR. However, the results suggest that D-CHO-S rarely affected the cholesterol transport in both species. The protein-protein interaction (PPI) network constructed on steroid biosynthesis-related DEG showed that in turbot, Msmo1, Lss, Nsdhl, Ebp, Hsd17b7, Fdft1, and Dhcr7 had high intermediary centrality in the dietary regulation of steroid synthesis. In conclusion, in both turbot and tiger puffer, the supplementation of dietary cholesterol inhibits the steroid metabolism but does not affect the cholesterol transport. [ABSTRACT FROM AUTHOR]

In aquaculture, drugs are often abused to accomplish disease control without considering the negative effects on fish health. This study aimed at elucidating the pernicious effects of in-feed antiparasitic drug emamectin benzoate (EB) abuse on the haemato-biochemistry and erythro-morphometry of healthy Nile tilapia Oreochromis niloticus. The fish were fed EB at 50 μg (1×) and 150 μg/kg biomass/d (3×) for 14 d as against the recommended 7 d and periodically assessed the blood parameters. A significant dose- and time-dependent reduction in feed intake, survival, total erythrocytes (TEC), monocytes (MC), hemoglobin (Hb), hematocrit (Ht) and mean corpuscular Hb concentration were noted. The total leukocytes (TLC), thrombocytes (TC), lymphocytes (LC) and neutrophils (NC) markedly augmented. The EB-dosing altered the fish physiology by enhancing the glucose, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and creatinine and reducing the calcium, chloride and acetylcholinesterase (AChE) levels dose-dependently. The fish recovered within 4 weeks in the 1× group post-dosing but persevered in the overdosed group. The erythro-cellular and nuclear dimensions were reduced with the increase in dose and normalized after the cessation of dosing, except for nuclear volume. The erythro-morphological alterations were more prominent in the overdosed group. The results implied the pernicious effect of oral EB medication on the biological responses of fish if abused. [ABSTRACT FROM AUTHOR]

Fish microbiota studies have mostly addressed intestinal bacterial communities because of their role in fish physiology; however, the skin microbiota has been studied less despite its role as the first pathogen barrier in the host. DNA-based molecular techniques have contributed to improving our understanding of the skin microbiota, but this approach faces challenges, such as the low count of bacteria in healthy fish skin. To overcome this limitation, an RNA-based approach was developed to study the skin microbiota in salmonids, including tissue sampling, RNA extraction, and downstream procedures to obtain PCR amplicons for next-generation sequencing. The protocol originated in this work overcomes the limitations of low bacterial counts and is useful for describing active microbiota in fish skin. The application of the protocol to salmonids reared in both an experimental setting and on a farm revealed that the trout skin microbiota was dominated by bacteria from the phylum Proteobacteria (>65%). At the genus level, Piscirickettsia (46%) was highlighted as the most abundant in the experimental unit samples; in contrast, Pseudoalteromonas (26%), followed by Escherichia_Shigella (~25%), was the most abundant in farmed trout. [ABSTRACT FROM AUTHOR]

Simple Summary: Consumption and excessive use of substances or items that are taken for granted in our daily lives such as personal care products, plastic objects, and medicines inevitably lead to their release into marine and freshwater systems with, unfortunately, potentially devastating consequences over time. For this reason, it is of crucial importance that the scientific community, as well as society, is aware of the environmental problems linked mainly to the release of contaminants into the sea. In this context, the Mediterranean Sea is a special biodiversity hotspot of marine fauna and flora. Nevertheless, it is becoming a source of concern due to the presence of emerging pollutants. In the present paper, the specific focus on the catshark Scyliorhinus canicula, as a vertebrate species, and on the Mediterranean mussel Mytilus galloprovincialis, as an invertebrate, lies in their ability to provide appropriate information about the health conditions of their surrounding environment. The studies reported on this topic show that it is rather evident that entire aquatic ecosystems suffer from anthropogenic pollution. Therefore, this review aims to collect and demonstrate its effects on the environment and organisms' health. In this historical context, the Mediterranean Sea faces an increasing threat from emerging pollutants such as pharmaceuticals, personal care products, heavy metals, pesticides and microplastics, which pose a serious risk to the environment and human health. In this regard, aquatic invertebrates and fish are particularly vulnerable to the toxic effects of these pollutants, and several species have been identified as bio-indicators for their detection. Among these, bivalve molluscs and elasmobranchs are now widely used as bio-indicators to accurately assess the effects of contaminants. The study focuses on the catshark Scyliorhinus canicular and on the Mediterranean mussel Mytilus galloprovincialis. The first one is a useful indicator of localised contamination levels due to its exposure to pollutants that accumulate on the seabed. Moreover, it has a high trophic position and plays an important role in the Mediterranean Sea ecosystem. The bivalve mollusc Mytilus galloprovincialis, on the other hand, being a filter-feeding organism, can acquire and bioaccumulate foreign particles present in its environment. Additionally, because it is also a species of commercial interest, it has a direct impact on human health. In conclusion, the increasing presence of emerging pollutants in the Mediterranean Sea is a serious issue that requires immediate attention. Bivalve molluscs and elasmobranchs are two examples of bio-indicators that must be used to precisely determine the effects of these pollutants on the marine ecosystem and human health. [ABSTRACT FROM AUTHOR]

With the purpose of improving aquaculture sustainability, the search for protein alternatives to fishmeal makes it necessary to test different variables and the possible repercussions of new ingredients. The use of insect meal as a protein source for aquaculture is well described, but the complex composition of insect meals (fat and other components) can affect the physiology of fish. For this reason, as a part of a bigger study, the aim of the current manuscript was to test diets based on three different presentations of insect meal coming from yellow mealworm (Tenebrio molitor): full fat, partially defatted, and supplemented with a long chain omega–3-enriched oil, and to evaluate their effects on protein digestibility, biometric indices, immunological system and gut health (intestinal histomorphology and microbiota) of rainbow trout (Oncorhynchus mykiss). Digestibility of the protein and body indices showed a minor but consistent trend. The non-specific immunological system did not show changes, but the histology of the intestine showed signs that insect meals could be softening a mild inflammatory response. The gut microbiota suffered several changes, which could be associated with the different amino acid and fatty acid compositions of the diets. [ABSTRACT FROM AUTHOR]

The regulation of lipid stores is a central process for the physiology and ecology of fishes. Seasonal variation in lipid stores has been directly linked to survival of fishes across periods of food deprivation. We assessed whether a seasonally changing photoperiod was correlated to seasonal changes in energetic status to help better understand these important processes. Groups of first feeding Chinook salmon fry were introduced to a seasonal photoperiod cycle, but the point of entrance into the seasonal cycle varied from near the winter solstice (December), to either side of the spring equinox (February & May). Temperature and feeding rate were similar for all treatments. Subsequently, condition factor and whole body lipid content were assessed through a seasonal progression. Throughout most of the experiment, length and weight did not differ between the different photoperiod treatments, however whole body lipid and Fulton's condition factor did. Furthermore, changes in both whole body lipid and Fulton's condition factor in all treatment groups followed a similar seasonal pattern that was inversely related to day length (highest K and lipid levels found during days with the least light). These results suggest that regardless of age or size, there is a correlation between seasonal changes in photoperiod and changes in body composition in juvenile Chinook salmonids. [ABSTRACT FROM AUTHOR]

I recently led a field study to assess how midshipman fish respond to motorboat noise while caring for eggs in their nests, using a real motorboat as a noise stimulus. I am studying the effect of motorboat noise on Plainfin Midshipman fish behavior and vocalizations - particularly their parental care, nest defense, and courtship. [Extracted from the article]

This review is focused on the questions of why fish exhibit heat failure at thermal extremes and which physiological mechanisms determine the acute upper thermal tolerance. We propose that rapid direct thermal impacts on fish act through three fundamental molecular mechanisms reaction rates, protein structure, and membrane fluidity. During acute warming, these molecular effects then lead to loss of equilibrium and death through various cellular, organ, and physiological pathways. These pathways include mitochondrial dysfunction, oxygen limitation, and impacted excitability of excitable cells and eventually lead to neural and/or muscular failure. The pathways may also lead to loss of homeostasis and subsequent heat failure. There is strong evidence in some species for oxygen limitation in these processes and strong evidence against it in other species and contexts. The limiting mechanisms during acute warming therefore appear to differ between species, life stages, and recent thermal history. We conclude that a single mechanism underpinning the acute upper thermal tolerance across species and contexts will not be found. Therefore, we propose future avenues of research that can elucidate major patterns of physiological thermal limitations in fish. [ABSTRACT FROM AUTHOR]

Temperature‐dependent sex determination (TSD) occurs when the temperature during development affects gonad determination. Historically, most work on TSD in fishes was conducted under constant temperatures, yet daily fluctuating temperatures can significantly alter fish physiology and life history. Thus, we subjected the Atlantic silverside, Menidia menidia (a TSD species), to 28, 28 ± 2 and 28 ± 4°C (a high, masculinizing temperature) and quantified sex ratios and length. We found that the percentage of females increased by 60%–70% when the fish were exposed to daily fluctuating temperatures (from 10% to 16% and 17% under fluctuations). [ABSTRACT FROM AUTHOR]

Evolution in the chronic cold of the Southern Ocean has had a profound influence on the physiology of cryonotothenioid fishes. However, the suite of genetic changes underlying the physiological gains and losses in these fishes is still poorly surveyed. By identifying the genomic signatures of selection, this study aims to identify the functional classes of genes that have been changed following two major physiological transitions: the onset of freezing temperatures and the loss of hemoproteins. Looking at the changes that followed the onset of freezing temperatures, positive selective pressure was found among a set of broadly acting gene regulatory factors, suggesting a route through which cryonotothenioid gene expression has been retooled for life in the cold. Further, genes related to the cell cycle and cellular adhesion were found under positive selection suggesting that both present key challenges to life in freezing waters. By contrast, genes showing signatures of the relaxation of selective pressure showed a narrower biological impact, acting on genes related to mitochondrial function. Finally, although chronic cold-water temperatures appear correlated with substantial genetic change, the loss of hemoproteins resulted in little observable change in protein-coding genes relative to their red-blooded relatives. Combined, the influence of positive and relaxed selection shows that long-term exposure to cold has led to profound changes in cryonotothenioid genomes that may make it challenging for them to adapt to a rapidly changing climate. [ABSTRACT FROM AUTHOR]

The gills are the major organ for Na+ uptake in teleosts. It was proposed that freshwater (FW) teleosts adopt Na+/H+ exchanger 3 (Nhe3) as the primary transporter for Na+ uptake and Na+-Cl− co-transporter (Ncc) as the backup transporter. However, convincing molecular physiological evidence to support the role of Ncc in branchial Na+ uptake is still lacking due to the limitations of functional assays in the gills. Thus, this study aimed to reveal the role of branchial Ncc in Na+ uptake with an in vivo detection platform (scanning ion-selective electrode technique, SIET) that has been recently established in fish gills. First, we identified that Ncc2-expressing cells in zebrafish gills are a specific subtype of ionocyte (NCC ionocytes) by using single-cell transcriptome analysis and immunofluorescence. After a long-term low-Na+ FW exposure, zebrafish increased branchial Ncc2 expression and the number of NCC ionocytes and enhanced gill Na+ uptake capacity. Pharmacological treatments further suggested that Na+ is indeed taken up by Ncc, in addition to Nhe, in the gills. These findings reveal the uptake roles of both branchial Ncc and Nhe under FW and shed light on osmoregulatory physiology in adult fish. [ABSTRACT FROM AUTHOR]

Pygocentrus nattereri is a widely distributed species in the Neotropical region and a potential bio-indicator. Kidneys have functions in fish physiology, allowing them to live in different environments. We aimed to compare the histological characteristics of caudal kidneys between males and females, associating them with the renosomatic index (RSI). For this purpose, 15 males and 14 females were used for biometric and histological analyses. Structural volumetric density (SVD), renal corpuscle histometric measures, and hemosiderin and lipofuscin deposit frequency in macrophages melanogenic (MMs) were assessed. No biometric differences were observed between the sexes, but body weight and standard length were correlated with RSI. The SVD showed difference in hematopoietic tissue between female and males, whereas the density of the other structures was not different. The RSI was positively associated with hematopoietic tissue and proximal tubule density in contrast to distal tubules, blood vessels, collecting ducts and MMs. Females exhibited a higher renal corpuscle area, glomerulus area, distal tubule diameter, collecting tubule area, and collecting tubule lumen area. These differences may be due to metabolic differences between males and females. Sex effect in P. nattereri may define punctual differences in future studies on the metabolism and immunity of this species. [ABSTRACT FROM AUTHOR]

Fish screens are structures associated with pump stations and power plants, that prevent entrainment of fish, but may also be a source of physiological stress, if placed in locations of strong flow speeds that fish are unable to sustain swimming against over time. Herein, the acute response of Anguilla anguilla and Oncorhynchus mykiss to a 30-minute exposure to two water flow regimes was evaluated at the lowest level of the hypothalamus–pituitary–interrenal axis, from blood serum and skin mucus, in a controlled setup presenting a 45° vertically-angled fish screen. Cortisol response was species specific, regardless of the matrix employed. While the flow velocity factor did not describe any variance of eel data, and no statistically significant differences in cortisol concentrations were observed among eel groups, cortisol release in response to flume hydraulics followed a dose-dependent pattern in trout, with a large proportion of the variance described by the model. Mucus cortisol was highly and strongly correlated to serum levels of trout specimens subjected to the strongest flow. Given the established neuromodulatory and molecular roles of cortisol on major fitness-relevant processes, animal welfare implications may be severe, especially considering ever increasing exposure to chronic anthropogenic stressors, resulting in repeated and/or prolonged elevation of circulating glucocorticoids. [ABSTRACT FROM AUTHOR]

Simple Summary: In the context of climate change, warming of the seas and expansion of hypoxic zones are challenges that most species of fish are, or will be subjected to. We provide first-time estimates on the metabolic rates, thermal, and oxygen-related limits for Halobatrachus didactylus, a coastal sedentary fish that lives in intertidal environments of the Northeast Atlantic. The metrics obtained in this study prove that H. didactylus is remarkably resilient to acute environmental variations in temperature and oxygen content, which might enable it to adapt to the extreme abiotic conditions forecasted for the world's oceans in the near future. In the context of climate change, warming of the seas and expansion of hypoxic zones are challenges that most species of fish are, or will be subjected to. Understanding how different species cope with these changes in their environment at the individual level can shed light on how populations and ecosystems will be affected. We provide first-time estimates on the metabolic rates, thermal, and oxygen-related limits for Halobatrachus didactylus, a coastal sedentary fish that lives in intertidal environments of the Northeast Atlantic. Using respirometry in different experimental designs, we found that this species is highly resistant to acute thermal stress (CTmax: 34.82 ± 0.66 °C) and acute hypoxia (Pcrit: 0.59–1.97 mg O2 L−1). We found size-specific differences in this stress response, with smaller individuals being more sensitive. We also quantified its aerobic scope and daily activity patterns, finding this fish to be extremely sedentary, with one of the lowest standard metabolic rates found in temperate fish (SMR: 14.96 mg O2 kg−1h−1). H. didactylus activity increases at night, when its metabolic rate increases drastically (RMR: 36.01 mg O2 kg−1h−1). The maximum metabolic rate of H. didactylus was estimated to be 67.31 mg O2 kg−1h−1, producing an aerobic scope of 52.35 mg O2 kg−1h−1 (77.8% increase). The metrics obtained in this study prove that H. didactylus is remarkably resilient to acute environmental variations in temperature and oxygen content, which might enable it to adapt to the extreme abiotic conditions forecasted for the world's oceans in the near future. [ABSTRACT FROM AUTHOR]

Locomotion is a defining characteristic that can dictate many aspects of an organism's life history in the pursuit of maximizing fitness, including escaping predators, capturing prey, and transitioning between habitats. Exhaustive exercise can have negative consequences for both short-term and long-term energetics and life history trade-offs, influencing fish survival and reproduction. Studies of swimming performance and exhaustive exercise in fish are often conducted on individual species, but few multispecies analyses exist and even fewer in field settings. In fish, swimming performance and exercise have historically been studied in the laboratory using swim tunnels, but an increasing body of work in recreational fisheries science provides a novel way to examine swimming capacity and exhaustion. Using fight time, the time it takes for a hooked fish to be landed on rod and reel fishing gear, as an opportunistic proxy for fish exhaustion, a multispecies meta-analysis of data from studies on recreational fisheries was conducted to elucidate the factors that most influence capacity for exhaustive exercise. Data from 39 species of freshwater and marine fish were aggregated, and negative binomial mixed effects models as well as phylogenetic least squares regression were used to identify the factors that most influenced exhaustive exercise in the field. Fish total length, aspect ratio of the caudal fin, and body form were significant factors in explaining the capacity for exhaustive exercise. Large migratory fish with high aspect ratios were able to fight, and therefore exercise, the longest. These results illustrate that body form and physiology are both deeply intertwined to inform function across fish species and point to angling fight time as a useful approximation of fish swimming capabilities that can be further developed for understanding the limits of fish exercise physiology. [ABSTRACT FROM AUTHOR]

Heavy metals have a high density that is harmful even in low quantity. These metals enter aquatic habitats through various sources, home effluents, including industrial waste, atmospheric sources, and other metal-based businesses, as well as EWaste. Heavy metal pollution is responsible for degenerating aquatic species, creating physical abnormalities in creatures and contaminating the aquatic environment. These poisonous heavy metals cause a variety of fish ailments like decrease in hatching rate, teratogenesis and bioaccumulation in the tissues etc. The contamination of heavy metals in aquatic bodies and ecosystems has a significant influence on the food chain. Because fish people consume fish, it has an indirect impact on their health. These heavy metals also have a higher impact on the environment because they remain for longer periods and have bio -accumulative capabilities, leading water health to deteriorate. This study offers insight into the disruption of fish and human physiology, their reproductive ability by heavy metals. This review provides baseline data on the heavy metals and aquatic environment, especially fish and human health. The data will increase sensitivity to preventing and managing aquatic environmental pollution, particularly heavy metal contamination. [ABSTRACT FROM AUTHOR]

Simple Summary: Vitamin K (VK), and particularly phylloquinone (VK1), is an essential micronutrient whose stability in aquafeeds has not been extensively evaluated. Losing stability can lead to nutritional deficiency, which is known to hamper fish development and physiology. Gut microbiota also plays a key role in host health through the interaction with several biological processes. The present study evaluated the best storing conditions of aquafeeds when supplemented in VK1 and intestinal microbiota modulation in Senegalese sole (Solea senegalensis) juveniles. Aquafeeds with a high level of VK1 supplementation required storage at −20 °C for short-term (up to 7 days) and at −80 °C for long-term (up to three months) to ensure optimal preservation. Furthermore, gut bacterial communities of Senegalese sole specimens fed with a commercial feed supplemented with VK1 showed a better-balanced population of microorganisms in the intestine, which might improve Senegalese sole health during the ongrowing phase. These results provide the practical guidelines for the proper storing of aquafeeds in the industry when supplemented with VK1 and highlight the potential benefits of dietary VK1 supplementation for a balanced intestinal microbiota and overall fish health. Vitamin K (VK) is a fat-soluble vitamin necessary for fish metabolism and health. VK stability as dietary component during aquafeed storage and its potential effect on intestinal microbiome in fish have not yet been completely elucidated. The convenient storage conditions of aquafeeds when supplemented with phylloquinone (VK1), as well as its potential effects on the gut microbiota of Senegalese sole (Solea senegalensis) juveniles, have been explored. Experimental feeds were formulated to contain 0, 250 and 1250 mg kg−1 of VK1 and were stored at different temperatures (4, −20 or −80 °C). VK stability was superior at −20 °C for short-term (7 days) storage, while storing at −80 °C was best suited for long-term storage (up to 3 months). A comparison of bacterial communities from Senegalese sole fed diets containing 0 or 1250 mg kg−1 of VK1 showed that VK1 supplementation decreased the abundance of the Vibrio, Pseudoalteromonas, and Rhodobacterace families. All these microorganisms were previously associated with poor health status in aquatic organisms. These results contribute not only to a greater understanding of the physiological effects of vitamin K, particularly through fish intestinal microbiome, but also establish practical guidelines in the industry for proper aquafeed storage when supplemented with VK1. [ABSTRACT FROM AUTHOR]

Predatory fish in the wild consume whole prey including hard skeletal parts like shell and bone. Shell and bone are made up of the buffering minerals calcium carbonate (CaCO3) and calcium phosphate (Ca3(PO4)2). These minerals resist changes in pH, meaning they could have physiological consequences for gastric acidity, digestion and metabolism in fish. Using isocaloric diets supplemented with either CaCO3, Ca3(PO4)2 or CaCl2 as non-buffering control, we investigated the impacts of dietary buffering on the energetic cost of digestion (i.e. specific dynamic action or SDA), gastric pH, the postprandial blood alkalosis (the "alkaline tide") and growth in juvenile rainbow trout (Oncorhynchus mykiss). Increases in dietary buffering were significantly associated with increased stomach chyme pH, postprandial blood HCO3−, net base excretion, the total SDA and peak SDA but did not influence growth efficiency in a 21 day trial. This result shows that aspects of a meal that have no nutritional value can influence the physiological and energetic costs associated with digestion in fish, but that a reduction in the SDA will not always lead to improvements in growth efficiency. We discuss the broader implications of these findings for the gastrointestinal physiology of fishes, trade-offs in prey choice in the wild, anthropogenic warming and feed formulation in aquaculture. [ABSTRACT FROM AUTHOR]

Water quality is crucial for maintaining a sustainable living environment in aquaculture. Limnological parameters affects the fish physiology, growth rate, and feed efficiency and may lead to high mortality rate under extreme conditions. The development of an adaptive aquaculture monitoring system for water quality using fuzzy logic will address this problem. Using Mamdani-type fuzzy inferences system (FIS) model, the input limnological parameters such as pH, temperature, total dissolved solids, and dissolved oxygen levels were transformed to four output states: excellent, good, poor, and toxic, for the prediction of water quality. For the simulation and evaluation of the developed FIS, MATLAB Simulink was used. Results of this study can be integrated with a feedback system for appropriate treatments including filtering, aeration, and water flushing to maintain safe environment for Nile tilapia. [ABSTRACT FROM AUTHOR]

Nephrocalcinosis is a common disorder in farmed Atlantic salmon, but the consequences for the fish physiology are not well understood. We performed a transcriptome study in kidneys of Atlantic salmon (Salmo salar) smolts without and with severe chronic nephrocalcinosis (NC). The study revealed that numerous genes are differentially expressed in fish with NC compared with healthy salmon. The most evident changes in gene expression patterns in the NC group were a massive downregulation of metabolism and energy production, upregulation of signalling pathways important for tissue repair and function maintenance and upregulation of inflammatory responses. Overall, the extensive tissue damage and the gene regulation responses that affect salmon with severe nephrocalcinosis are highly likely to have dramatic consequences on fish survival. [ABSTRACT FROM AUTHOR]

Vitamin C (VC) is a necessary nutrient for normal fish physiology and immunity. Therefore, A 60‐day feeding trial was designed to evaluate the dietary VC requirements of silver carp (Hypophthalmichthys molitrix). Six isocaloric and isonitrogenous diets were formulated by incorporation of VC at 0, 50, 100, 200, 400 and 800 mg kg−1 levels and the analysed VC content in diet was 5.7, 51.1, 95.3, 191.6, 370.7 and 757.5 mg kg−1 respectively. At the trial termination, VC supplementation significantly enhanced the growth and feed utilization. The highest values for whole body crude protein were recorded at 95.3 and 191.6 mg kg−1 of VC. In comparison to the basal diet, VC supplementation improved (p < 0.05) the whole body crude fat. Dietary VC had a dose‐dependent effect on the white blood cell count and haematocrit. A significant increase in the alkaline phosphatase activity was recorded for fish fed 5.7 to 95.3 mg kg−1 of VC, attaining a constant value afterwards (95.3–757.5 mg kg−1 of VC). In comparison, dietary VC decreased (p < 0.05) the aspartate aminotransferase and alanine aminotransferase activities. Similarly, the glucose content also decreased significantly from 5.7 to 95.3 mg kg−1 of VC and became constant thereafter. Dietary VC supplementation significantly affected the antioxidant enzyme activities. The liver VC content showed a dose‐dependent relation, where the VC content increased with the increase in VC supplementation reaching the highest value at 757.5 mg kg−1. Moreover, VC‐fed fish showed an increased (p < 0.05) survival against Aeromonas hydrophila challenge. On the basis of broken‐line regression, the optimum dietary VC requirement of H. molitrix for weight gain% and liver VC content is 61.31 and 241.13 mg kg−1 respectively. [ABSTRACT FROM AUTHOR]

Resolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size‐structure and potential yields of marine fishes. Previous studies based on mechanistic size‐based food web models have found that bottom‐up processes are important drivers of size‐structure and fisheries yield in changing climates. However, we know less about the joint effects of 'bottom‐up' and physiological effects of temperature; how do temperature effects propagate from individual‐level physiology through food webs and alter the size‐structure of exploited species in a community? Here, we assess how a species‐resolved size‐based food web is affected by warming through both these pathways and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size‐structure, and relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4‐NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature‐effects on physiology in addition to on basal productivity, projected size‐at‐age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size‐at‐age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in decline in the abundance of larger fish and hence spawning stock biomass. These results suggest that to understand how global warming affects the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for. [ABSTRACT FROM AUTHOR]

Simple Summary: Zoos and aquaria play an important role in preventing the mass extinction of wildlife through public awareness of conservation issues and providing a safe haven for wildlife populations. Because aquatic populations face many challenges due to pollution and global warming, it is important to develop an understanding of how species can cope with their environment whether it be in the wild or under human care. Here, we were interested in developing non-invasive methods to study fish stress physiology. We use the unique ocean sunfish (Mola mola) to develop the use of skin swabs to measure the stress hormone, cortisol. We used known times of stress including when a mola was injured or ill and during acclimation to the Monterey Bay Aquarium. We found that cortisol increased initially within the first month of being admitted to the aquarium, but returned to normal values afterward. Molas also had elevated cortisol when being treated for an injury or illness. This is the first step in the development of the use of skin swabs to collect samples for stress analysis in the mola. Additional biochemical analysis is needed to confirm these results and allow this method to be applied to other species of fish. The ocean sunfish (mola; Mola mola) is the heaviest bony fish in the world. This slow-moving fish often is injured by fishing boats that use drift gillnets attributing to its listing as Vulnerable by the IUCN. The Monterey Bay Aquarium (Monterey, CA, USA) has a program that brings in smaller molas from the ocean and acclimates them for an exhibit. When they grow too large for the million-gallon Open Seas exhibit, they are returned to Monterey Bay through a "reverse" acclimatization. Our overall goal was to use skin swabs to evaluate mola stress physiology to better understand the effects of this program. Our objectives were to validate this non-invasive method by taking opportunistic swabs throughout acclimatization and during stressful events. We swabbed each individual (n = 12) in three different body locations. Swabs were analyzed using a cortisol enzyme immunoassay. We averaged the three swabs and examined the absolute change of cortisol from the first taken upon handling to during treatments and the different acclimation stages. We considered elevated cortisol concentrations to be ≥1.5-fold higher than the first sample. Overall, mean (±SEM) cortisol varied among individuals (564.2 ± 191.5 pg/mL swab (range, 18.3–7012.0 pg/mL swab). The majority (four of six) of molas swabbed within the first week or month had elevated skin cortisol compared to their first sample. All seven molas that were being treated for an injury or illness had elevated skin cortisol (range, 1.7- to 127.6-fold higher) compared to their post-acclimation sample. This is the first step in validating the use of non-invasive skin swabs for glucocorticoid analysis in the mola. Further biochemical analysis is needed to determine the specific steroids that are being measured. [ABSTRACT FROM AUTHOR]

The study was conducted to evaluate the efficacy of biofloc meal incorporated diets on growth performance and physiological responses in Penaeus vannamei. The feeding trial was conducted using two control diets and four experimental diets, having biofloc meal at various incorporation levels, namely control diet (commercial diet), BFT0 (biofloc meal control, biofloc meal at 0%) BFT10 (biofloc meal at 10%), BFT20 (biofloc meal at 20%), BFT30 (biofloc meal at 30%), and BFT40 (biofloc meal at 40%). Healthy post larvae of P. vannamei (0.03 ± 0.00 g) were stocked (50 shrimp per tank) in a glass tank and fed with the experimental diets at 10% of animal body weight, four times a day, for a duration of 60 days. Among the different treatments, significantly higher final body weight (1.30 ± 0.06 g), weight gain (1.27 ± 0.06 g), specific growth rate (6.21 ± 0.01%/day), and survival rate (62 ± 0.20%) were recorded in BFT30 diet. In contrast, shrimp reared using control diet exhibited lower specific growth rate (5.53 ± 0.02%/day) and survival (48 ± 0.14%) compared to other treatment groups. At the end of the experiment, serum protein (1.6 ± 0.02 g/dl), prophenoloxidase (16.35 ± 2.98 U/mg protein), and peroxidase (0.2 ± 0.03 U/ml) were found to be significantly higher in BFT30 diet-fed group. Similarly, the digestive enzyme activities of amylase (4.75 ± 0.87 U/mg protein) and lipase (118 ± 5.10 U/mg protein) of BFT30 reared shrimp were found to be significantly higher. In addition, the histological observation of the shrimp revealed the larger proportion of mature cells with intracellular digestion (B) and absorption (R) in BFT30 group. Overall, the study revealed that biofloc meal incorporation at 30% in shrimp diet would potentially improves the growth performance and physiological responses of shrimp. [ABSTRACT FROM AUTHOR]