Fish Physiology Research Articles

Unraveling the Impact of Climate Change on Fish Physiology: A Focus on Temperature and Salinity Dynamics

In recent decades, climate change has significantly altered the environmental dynamics of aquatic ecosystems, profoundly impacting the intricate balance of life within them. This review paper delves into the multifaceted impacts of climate change on the physiology of aquatic life, emphasizing temperature and salinity as pivotal ecological factors unique to aquatic environments. The intricate relationship between rising global temperatures and their repercussions on freshwater and seawater habitats forms the cornerstone of this exploration. Elevated temperatures and escalating frequency of extreme heatwave events have reshaped the paradigm for fish survival, pushing them beyond optimal temperature thresholds. Furthermore, the study delves into the interconnection of seemingly disparate abiotic factors, where heightened greenhouse gas concentrations amplify coastal winds, precipitating coastal upwelling. The consequence—nutrient‐rich yet oxygen‐deprived waters—fuels a cascade of challenges, inducing hypoxic conditions that significantly impact aquatic organisms. The plight of fish, as ectotherms finely tuned to environmental fluctuations, is underscored, illuminating their susceptibility to temperature variations. The direct correlation between external and internal temperatures, exacerbated by climate‐induced fluctuations, accentuates the urgency of addressing climate change’s impact on aquatic habitats. This review disentangles the complex web of interconnected environmental shifts, illuminating their far‐reaching repercussions on the physiology of aquatic life. It emphasizes the imperative for collective endeavors aimed at understanding and addressing the challenges imposed by our evolving climate on these indispensable ecosystems.

Evaluation of the Effect of Dietary Manganese on the Intestinal Digestive Function, Antioxidant Response, and Muscle Quality in Coho Salmon.

Manganese (Mn) is a nutritional element required for fish growth and physiology functions. In this study, we examined the effect of Mn on the intestinal digestive function, antioxidant response, and muscle quality in coho salmon (Oncorhynchus kisutch). Nine hundred salmons with initial weight approximately 0.35 g were fed with six isoproteic and isoenergetic diets formulated to contain 2.4, 8.5, 14.8, 19.8, 24.6, and 33.7 mg/kg Mn for 84 days. The result showed that the activity of trypsin and lipase was elevated, whereas α-amylase activity was not affected by various Mn diets in intestine. Dietary Mn elevated the activity of Mn-superoxide dismutase (Mn-SOD), total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-PX), and catalase (CAT), but had no influence on copper/zinc-superoxide dismutase (Cu/Zn-SOD) in intestine. Dietary Mn at 8.5, 14.8, 19.8, 24.6, and 33.7 mg/kg enhanced the gene expression level of protein kinase B (Akt) and mammalian target of rapamycin (mTOR). In addition, the accumulation of Mn in muscle was enhanced with increasing levels of dietary Mn. Dietary Mn elevated the content of sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca), but the content of iron (Fe) and Zn was decreased by dietary Mn in the salmon muscle. The content of fatty acids and amino acids was enhanced by various levels of dietary Mn in muscle. Moreover, a significant quadratic effect was observed on the texture of salmon muscle. The dietary Mn requirement was 16.9-25.7 mg/kg Mn to acquire the highest value of muscle texture using the quadratic regression model. The diets at 14.8 and 19.8 mg/kg Mn had a higher score of sensory evaluation for raw muscle. Our result showed that dietary Mn affected the intestinal digestion function and antioxidant response, which may further result in the change of muscle quality in coho salmon. The result will provide reference for detecting the effect of dietary micronutrients on the muscle quality of salmons.

Interactive effects of sedimentary turbidity and elevated water temperature on the Pugnose Shiner (Miniellus anogenus), a threatened freshwater fish.

High turbidity and elevated water temperature are environmental stressors that can co-occur in freshwater ecosystems such as when deforestation increases solar radiation and sedimentary runoff. However, we have limited knowledge about their combined impacts on fish behaviour and physiology. We explored independent and interactive effects of sedimentary turbidity and temperature on the swimming activity and both thermal and hypoxia tolerance of the Pugnose Shiner (Miniellus anogenus, formerly Notropis anogenus), a small leuciscid fish listed as Threatened under Canada's Species at Risk Act (SARA). Fish underwent a 15-week acclimation to two temperatures (16°C or 25°C) crossed with two turbidities (~0 NTU or 8.5 NTU). Swimming activity was measured during the first 8weeks of acclimation. Fish in warm water were more active compared to those in cold water, but turbidity had no effect on activity. Behavioural response to hypoxia was measured after 12weeks of acclimation, as the oxygen level at which fish used aquatic surface respiration (ASR). Fish in warm water engaged in ASR behaviour at higher oxygen thresholds, indicating less tolerance to hypoxia. Turbidity had no effect on ASR thresholds. Finally, thermal tolerance was measured as the critical thermal maximum (CTmax) after 13-15weeks of acclimation. Acclimation to warm water increased fish CTmax and Tag (agitation temperature) but reduced the agitation window (°C difference between Tag and CTmax) and thermal safety margin (°C difference between the acclimation temperature and CTmax). Furthermore, fish in warm, turbid water had a lower CTmax and smaller thermal safety margin than fish in warm, clear water, indicating an interaction between turbidity and temperature. This reduced thermal tolerance observed in Pugnose Shiner in warm, turbid water highlights the importance of quantifying independent and interactive effects of multiple stressors when evaluating habitat suitability and conservation strategies for imperilled species.

High water temperature significantly influences swimming performance of New Zealand migratory species.

Anthropogenic structures in freshwater systems pose a significant threat by fragmenting habitats. Effective fish passage solutions must consider how environmental changes introduce variability into swimming performance. As temperature is considered the most important external factor influencing fish physiology, it is especially important to consider its effects on fish swimming performance. Even minor alterations in water properties, such as temperature and velocity, can profoundly affect fish metabolic demands, foraging behaviours, fitness and, consequently, swimming performance and passage success. In this study, we investigated the impact of varying water temperatures on the critical swimming speeds of four migratory New Zealand species. Our findings revealed a significant reduction in critical swimming speeds at higher water temperatures (26°C) compared to lower ones (8 and 15°C) for three out of four species (Galaxias maculatus, Galaxias brevipinnis and Gobiomorphus cotidianus). In contrast, Galaxias fasciatus exhibited no significant temperature-related changes in swimming performance, suggesting species-specific responses to temperature. The cold temperature treatment did not impact swimming performance for any of the studied species. As high water temperatures significantly reduce fish swimming performance, it is important to ensure that fish passage solutions are designed to accommodate a range of temperature changes, including spatial and temporal changes, ranging from diel to decadal fluctuations. Our research underscores the importance of incorporating temperature effects into fish passage models for habitat restoration, connectivity initiatives, and freshwater fish conservation. The influence of temperature on fish swimming performance can alter migration patterns and population dynamics, highlighting the need for adaptive conservation strategies. To ensure the resilience of freshwater ecosystems it is important to account for the impact of temperature on fish swimming performance, particularly in the context of a changing climate.

Assessing Seasonal Changes in Physicochemical Traits and Biochemical Profiles of Key Carp Species in Masani Barrage Lake and JLN Canal

Our thorough seasonal analysis of Masani Barrage Lake and JLN Canal in Rewari reveals the profound impact of seasonal changes on aquatic ecosystems. Both water bodies display distinct patterns in temperature, pH, salinity, and other parameters. The unique characteristics of lakes, with greater temperature fluctuations and nutrient cycling, contribute to differences in phytozooplankton and ecological dynamics compared to more regulated canals. Additionally, our study on common carp tissues shows clear seasonal variations in moisture, ash, protein, lipid, and fatty acid levels, indicating specific metabolic responses to environmental conditions. Understanding these nuances is crucial for grasping the diverse influences of these habitats on fish physiology, with lakes experiencing more significant variations than canals due to their larger and more open systems.

Dietary alpha-lipoic acid boosts growth, immune-antioxidant traits, behavior, and transcriptomes of antioxidant, apoptosis, and immune-related genes to combat cold stress in Nile tilapia (Oreochromis niloticus)

Water temperature is a major environmental factor affecting fish activity, physiology, behavior, and growth. Alpha lipoic acid (ALA) has garnered much attention lately as an aqua feed supplement because of its antioxidant effects. Thus, this study aimed to assess the effect of dietary ALA on performance, hematological and immunological indices, behavior and oxidative stress, apoptosis, and genetic inflammation in Oreochromis niloticus following 60 days of cold stress. Two hundred forty fish were divided into four groups (15 fish/replicate, N = 60 fish/group). The control (CNT) and ALA groups were reared at 25 °C and fed a basal diet without any supplementation or a basal diet containing 600 mg ALA/kg diet, respectively. The cold water-stressed group (CWS) and ALA + CWS groups were reared at 18 °C and fed basal and basal diets containing ALA, respectively. The results revealed that dietary ALA supplementation significantly improved feed utilization and growth in fish. ALA also mitigated CWS-induced microcytic hypochromic anemia and hyperlipidemia. Moreover, ALA supplementation considerably enhanced the antioxidant status and boosted intestinal α amylase, lipase, protease, and serum acetylcholinesterase activity of CWS-exposed fish. Besides, ALA supplementation significantly reversed CWS-induced upregulation of proinflammatory genes, pro-apoptotic genes, heat shock protein, and proliferating cell nuclear antigen or downregulation of superoxide dismutase and catalase gene expressions in liver and spleen tissues. Furthermore, ALA supplementation reduced CWS-induced histopathological alterations in fish liver, spleen, and intestine. We can conclude that ALA (600 mg/kg diet) could be recommended as an aqua feed supplement to boost growth, antioxidant capacity, and immunity and attenuate inflammatory and apoptotic reactions of fish reared under CWS-induced.

Central pattern generators for biomorphic robotics

Typically, the structure of the robot fish frame significantly differs compared to the real organism. One significant difference is in the number of body segments. While live fish can have between 16 (moon fish) to 400 belt fish [1] segments, robots usually have only 5–6 segments since substantial precision is unnecessary when simulating movement. At the same time, this method limits a significant portion of the control circuit’s structure compared to a fish’s nervous system because it only requires control over a smaller number of body segments. Control systems using different oscillators can simulate the functioning of fish central generators [2–4]. Typically, each half-center of the fish’s CPGs is interconnected with and mutually inhibitory towards the others, with each being responsible for the antagonist muscles. In this case, the generator’s pattern characteristics stem from the mutual influence of oscillator-antagonist pairs connected to each other. The half-centers’ interaction mechanism with each other is designed to match the movement pattern’s desired final parameters. This “artificial” approach is unsuitable for working with spike neurons because the mechanisms of cellular interaction are well-defined. Altering how cells interact with each other when creating a biologically relevant model is also undesired. Here we present evidence that incorporating select physiological traits of fish into the design of a CPG structure utilizing spike neurons can enhance the system’s functional capacity. Previously, we demonstrated a half-center CPG model using Izhikevich neurons [5]. This model can serve as a control loop for a tuna robot. Although this development aligns with the fundamental principles of CPG organization in fish, reproducing the typical generator mode of operation for pike on it proved challenging. This is due to the fact that the anguliform type of locomotion implies the presence of a moving wave, which means a phase lag in the activation of half-centers. One potential solution to the problem lies in the physiology of fish, specifically the structure of their muscle fibers. Fish have muscle segments called myomeres, which correlate with the number of vertebrae and spinal centers that create the CPG. A distinguishing feature of these myomeres is their zigzag shape. To achieve body bending at a single point, it requires a collaborative action between multiple myomeres and corresponding CPG segments. While our model assumes control of the entire fish with only 5 segments of the CPG, the actual pike includes 56–65 segments. To attain the necessary difference in activation phase between generator segments, we propose increasing the number of generator nodes responsible for operating a single propulsion unit. Indeed, increasing the number of transmission segments resulted in a steady divergence in activation phases among successive segments of the CPG. However, the incorporation of supplementary segments fails to address the challenge of managing the frequency of the CPG’s operation and shifting between patterns. Consequently, we intend to integrate CPG neurons of diverse types outlined in the model, along with introducing feedback to rectify its modes of operation in the future.

Translational neurobiology of zebrafish (<i>Danio rerio</i>)

The zebrafish (Danio rerio) is a small freshwater teleost fish species that is increasingly utilized in biomedical research, particularly in neuroscience and biological psychiatry. Currently, zebrafish is the second-most utilized model organism in biomedicine globally, after mice, based on the number of animals tested each year. The model’s significance results from its experimental ease of use, affordability, conservation of fish physiology, relatively high genetic homology with humans (70%), rapid development, and potential for high-throughput bioscreening of drugs and genetic mutations. Over the past 15 years, our laboratory has conducted extensive experimental work to establish the principles behind using zebrafish to study various brain pathologies, including acute and chronic stress, anxiety, and depression, as well as probing their molecular mechanisms. In addition, existing behavioral models to study the central nervous system (CNS) development and new data on the zebrafish’s critical role in memory research were reviewed. Furthermore, this study will illustrate the effectiveness of integrating zebrafish models with advanced biological research techniques, such as molecular biology, bioinformatics, omics technologies, and chemical biology methods. For example, adult zebrafish experiencing chronic stress exhibit behavioral affective syndromes along with changes in neurochemistry, specifically in the metabolism of serotonin and dopamine in the telencephalon. Moreover, alterations in the expression of genes regulating neurotransmitter receptors, glial biomarkers, cytoskeleton, and pro- and anti-inflammatory cytokines, occur in the brain. In particular, we will focus on neuroimmune and epigenetic mechanisms of CNS pathogenesis in zebrafish models, including changes in the expression of apoptotic genes in the brain. Additionally, our own findings on using artificial intelligence (AI) systems to study zebrafish behavior after administering various neurotropic drugs, such as anxiolytics, antidepressants, psychostimulants, and hallucinogens will be presented. In general, zebrafish is a strategic and promising model organism for translational neuroscience research, creating new models of CNS pathogenesis and finding new drugs to treat various human brain diseases. Studies of CNS pathogenesis in zebrafish are critical because of their evolutionary conservatism and ease of laboratory application, revealing novel brain disease biomarkers and potential remediation targets. Meanwhile, certain distinctive aspects of the biology and neurophysiology of zebrafish facilitate the resolution of supplementary experimental issues, thereby enhancing data and discoveries attained in typical animal models using rodents.

Swimming Performance of Schizothorax sp. and Planning of Fish Passages in Nepal

Swimming performance of migrating fish is crucial for the planning and design of effective fish passages. Commonly the fish swimming speeds are classified into five categories: 1) Optimum Swimming Speed, 2) Maximum Sustained Swimming Speed, 3) Critical Swimming Speed, 4) Maximum Domed Swimming Speed, and 5) Burst Swimming Speed. Swimming characteristics are related to the different species' adaptions to the environmental conditions. A variety of different factors affect the swimming capacity of fish which is directly related to fish size and species-specific morphology. A crucial abiotic factor is water temperature, which affects the fish physiology and thereby the swimming speed of the fish. This means that the fish's swimming speed can increase with increased water temperature. The swimming speed also increases with fish size. Fish often use burst speeds when passing a step in a fish ladder or entering a culvert. Burst speed is the highest speed attainable for fish, and it is the maximum energy output to be gained by using the white muscle (red muscle in salmonids). The burst speed can only be maintained for short periods of time (seconds). In the Himalayas, the main objective of many fisheries development plans is to secure future habitats and ensure up- and downstream migration of fish. Schizothorax richardsonii is often a targeted species in the area due to its importance as a food resource. If a fish passage is prepared for the upstream migration of fish, it is also crucial for the fish population development to ensure a safe downstream passage. Data on swimming performance for many of the native fish species in Nepal are scarce which complicates the design of suitable ecologically adapted fishways. In general, nature-like fish passes allow most of the species to migrate, followed by vertical slot fishways, meander fishways, and thereafter fish ladders of the pool-and-weir type. The key factor is to construct fish-passes that under all naturally required environmental circumstances can allow appropriate passage conditions of the targeted fish species.

Studies on Histopathological Alterations in the Brain and Gill, of <i>Cyprinus carpio</i> Exposed to the Insecticide Afidopyropen

The histopathology of the brain and gill tissues of the fish Cyprinus carpio following exposure to afidopyropen was determined by light microscopy. This particular carp species is one of the most prevalent in India. Afidopyropen (0.2 mg/L) was administered to fish for 1, 10, 20, and 30 days as part of an experiment. The tissues in the control group were found healthy. The abnormalities in the brain were Neural Degeneration (ND) Pyknotic Neuron (PN) Necrotic Internal Granule Cells (NIGC) Demyelination (DM). In gill tissues exposed to afidopyropen, hyperplasia, telangiectasia, epithelial separation, and total destruction of lamellae were seen. In the current study, afidopyropen damaged the organs, indicating its potential for harm. There were no sudden histological changes in one day-exposed group of the fishes. It could be due to healthy fish’s strong and quick adaptation capacity. The severity of stress and the associated histological changes would likely increase over time as the exposure to afidopyropen continues. However, prolonged exposure to the toxicant extremely affects the fish physiology leading to the form of above said pathological lesions.

Responses to graded levels of zinc amino acid complex in Nile tilapia (Oreochromis niloticus).

Zinc (Zn) is an essential micronutrient that plays a crucial role in fish development and physiology. This study aimed to evaluate the effects on growth and health in Nile tilapia (Oreochromis niloticus) supplemented with graded levels of zinc amino acid complex (Zn-AA) and subjected to transport stress. Nile tilapia (21.78 ± 0.17g; (n = 12 fish per tank; stocking density of 1.045kg- 3) were fed with 0, 25, 50, 75, or 100mg Zn-AA kg- 1 (equivalent to 77.49, 102.69, 127.89, 153.09, or 178.29mg Zn kg- 1) in extruded diets (280g kg- 1 digestible protein; isoproteic and isocaloric) for 60 days. At the end of the experimental period, after growth performance measurements, the fish were transported by car for 3h, and blood collection was performed. The linear regression showed that the best growth performance (final weight, final biomass, weight gain, specific growth rate, and feed intake) was found in fish fed with 100mg Zn-AA kg diet- 1 (p < 0.05). The increased dietary Zn-AA increased linearly plasma triglyceride levels, hemoglobin, mean corpuscular hemoglobin, and leukocyte values and reduced plasma total protein, cholesterol (total and LDL), and aspartate aminotransferase levels (p < 0.05). According to quadratic regression, the highest plasma glucose and alanine aminotransferase values were found in the control group (p < 0.05). In conclusion, under the conditions of this study, 100mg Zn-AA kg diet- 1 is recommended for Nile tilapia as it can improve their growth, metabolism, physiology, and immunity.

Time of day-dependent effects of heat treatment on thermal tolerance and sex differentiation in Nile tilapia (Oreochromis niloticus)

The present research aimed to determine the influence of the time of day at which heat treatment (HT) is applied to sexual differentiation and thermal tolerance mechanisms in Nile tilapia (Oreochromis niloticus). To this end, fish larvae were subjected to HT (36 °C) for 12 days at different times of the day during the thermosensitive period (i.e. 11–23 days post-fertilization, dpf). The heat treatment was applied during the light phase (L-HT); during the dark phase (D-HT), or during both light-dark phases (LD-HT). A control group maintained at constant rearing temperature (28 °C, CTRL) was also used. At 25 dpf, thermal tolerance was determined (survival) and whole larvae samples were collected for the mRNA expression analysis (qPCR). There after, all the groups remained at constant temperature until 270 dpf, when some fish were sacrificed and each individual's gonadal lobules were collected for histological and qPCR analyses. At the same time, each experimental group was subjected to acute heat shock (HS; 36 °C for 2 h) in either the mid-light (ML) or the mid-dark (MD) phase. When HS exposure finished, adults' brains were extracted to determine the HS response by qPCR. The expression of the genes involved in female (cyp19a1a, foxl2, era) and male (amh, ara, sox9a, dmrt1) sexual differentiation and thermal tolerance (hsp70, hsp90a, hsp27) in the 25 dpf larvae and adults was studied. The results revealed that all the HT-treated larvae showed an up-regulation of testicular differentiation gene expression and inhibition of ovarian differentiation gene expression, which resulted in a higher percentage of males. The time of day of HT during development influenced thermotolerance in the larval and adult stages, with the lowest survival and highest cellular stress (higher HSPs expression) observed in the larvae of the D-HT and LD-HT groups. These findings reveal the need to further investigate the link between sexual differentiation and thermotolerance daily rhythms in thermal biology research. These results may be useful for optimizing masculinization protocols in the tilapia industry, while ensuring animal welfare and minimizing negative HT effects on fish physiology.

Insights on Fish Gut Microbiome - A Review

Fish continues to attract considerable scientific interest as they are the most diverse community of vertebrates and a major component of a growing global aquaculture market. Complex assemblages of microbes, collectively known as the gut microbiota, colonize the digestive tracts of vertebrates. The gut microbiome plays a key role in fish health by stimulating immune system growth, assisting in the acquisition of nutrients, and outcompete opportunistic pathogens. Key innovations in recent years include the incredible rise in research of microbiomes, driven by advances in high-throughput sequencing technologies. The manipulation of fish gut microbiota to increase health and diet is gaining popularity. To date, most research in this area has concentrated on humans, and our knowledge of the microbiota in fish guts is minimal. This review gives an insight into the research of fish gut microbiota, including their development, variation with habitat, factors affecting gut microbial composition, their role in fish physiology, methods of characterization, application and research gaps, which can guide the development of probiotics, prebiotics and other novel additives to improve the production of healthy fish, and promote sustainable aquaculture.

Exposure metanil yellow as textile dye

The textile industry is one of the fastest growing industries today. The more the textile industry, the more dye waste is generated. Waste that is not managed properly and is wasted in the waters can cause pollution. Fish that are commonly found in freshwater are the Cichlid group, one of which is tilapia (Oreochromis niloticus) which can be exposed to textile dye waste. Exposure to chemical-based textile dye waste can affect fish physiology, including the formation of fish bones when fish are growing. This can be seen from the results of research on the description of malformation of tilapia exposed to metanil yellow textile dye. This research is an experimental study on juveniles conducted in the laboratory for one month. The results showed that there were malformation in the cephal, truncus and caudal tilapia.

From Fish Physiology to Human Disease: The Discovery of the NCC, NKCC2, and the Cation-Coupled Chloride Cotransporters.

The renal Na-K-2Cl and Na-Cl cotransporters are the major salt reabsorption pathways in the thick ascending limb of Henle loop and the distal convoluted tubule, respectively. These transporters are the target of the loop and thiazide type diuretics extensively used in the world for the treatment of edematous states and arterial hypertension. The diuretics appeared in the market many years before the salt transport systems were discovered. The evolving of the knowledge and the cloning of the genes encoding the Na-K-2Cl and Na-Cl cotransporters were possible thanks to the study of marine species. This work presents the history of how we came to know the mechanisms for the loop and thiazide type diuretics actions, the use of marine species in the cloning process of these cotransporters and therefore in the whole solute carrier cotransproters 12 (SLC12) family of electroneutral cation chloride cotransporters, and the disease associated with each member of the family.

Bergmann patterns in planktivorous fishes: A light‐size or zooplankton community‐size rule is just as valid explanation as the temperature‐size rule

AbstractAimBergman patterns, the tendency of organisms to be larger at higher latitudes and lower temperatures, are a well‐studied biogeographic pattern. Yet, there is no consensus on the driver or underlying mechanisms. We aim to scrutinize the influence of several key proposed drivers of Bergmann patterns (temperature, seasonal light availability, prey size and seasonal abundance) on optimal body size in planktivorous fishes across high latitudes in the Northeast Atlantic.LocationNortheast Atlantic between 55 and 75° N, with implications for high‐latitude oceans globally.Time periodPresent day.Major taxa studiedPelagic planktivorous fishes, with Atlantic herring (Clupea harengus) as model organism.MethodsWe use a model that incorporates explicit mechanisms for vision‐based feeding and temperature‐dependent physiology of a planktivorous fish to explore how intrinsic and extrinsic constraints affect energy budgeting and thereby expected optimal body size based on bioenergetics. We run the model at latitudes with increasing seasonality and test the individual and joint effects of relevant drivers.ResultsA Bergmann pattern emerges from the interaction between visual feeding opportunities and temperature‐dependent physiology. Small individuals profit from faster energy processing at higher temperatures in the south, whereas large individuals benefit from a lower metabolic cost at colder temperatures and more daylight hours for feeding in the north. In isolation temperature, daylight hours, and prey size each produced Bergmann patterns, but the most pronounced pattern arose from all drivers combined.Main conclusionsStudying biogeographic body size patterns requires a holistic view, accounting for interactions between drivers and both intrinsic and extrinsic constraints on energy budgeting. Across latitudes, temperature effects on digestion and metabolism interact with effects of light availability, prey size and abundance on food accessibility, and thereby shape the optimal size. Our study highlights how details of ecological mechanisms and lifestyles are important for improving predictive ability.

Effects of acute hypoxic post-feeding condition on respiratory metabolism and digestion in yellow catfish (Pelteobagrus fulvidraco)

In this study, acute hypoxia was applied to two states of yellow catfish (Pelteobagrus fulvidraco) (non-feeding and feeding) for 48 h. We investigated the effects of acute hypoxia on the respiratory metabolism and digestive ability of yellow catfish (mean body length: 7.61 ± 0.52 cm). The results indicated that the respiratory frequency of yellow catfish under acute hypoxic post-feeding condition was rapidly accelerated and the oxygen consumption rate was reduced. The level of succinate dehydrogenase in the gills first increased and then significantly decreased (p < 0.05) and the level of lactate dehydrogenase significantly increased (p < 0.05). When the expression level of hypoxia-inducing factor was significantly increased (p < 0.05), the downstream coding genes (hexokinase 1 (hk1), phosphofructokinase (pfkla), and pyruvate kinase M1/2a (pkma)), key molecules of glycolysis, and the activity of crucial enzymes (hexokinase, phosphofructokinase, and pyruvate kinase) increased. At the same time, the glucose level dropped and the lactic acid level increased, indicating that the metabolic mode in the gills of yellow catfish under acute hypoxic post-feeding condition gradually changed to anaerobic, and the anaerobic glycolysis process was activated to provide the required energy for the body. In addition, we found that the activity of digestive enzymes (trypsin, lipase, and amylase) and expression levels of digestive genes (trypsin, lipase, and amylase) were inhibited in the liver and intestine of yellow catfish under the acute hypoxic post-feeding condition, indicating that their digestive ability was reduced. This may adversely affect growth and development. This study analyzed the effects of acute hypoxic post-feeding exposure on the respiratory metabolism and digestive capacity of yellow catfish, providing new insights into fish physiology and sustainable fish culture.

Dietary supplementation with Lippia sidoides essential oil improves organ integrity but the specific activity of antioxidant enzymes is dose-dependent in Danio rerio.

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 supplementationand 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, kidneyand 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.

An Astyanax mexicanus mao knockout line uncovers the developmental roles of monoamine homeostasis in fish brain.

Monoaminergic systems are conserved in vertebrates, yet they present variations in neuroanatomy, genetic components and functions across species. MonoAmine Oxidase, or MAO, is the enzyme responsible for monoamine degradation. While mammals possess two genes, MAO-A and MAO-B, fish possess one single mao gene. To study the function of MAO and monoamine homeostasis on fish brain development and physiology, here we have generated a mao knockout line in Astyanax mexicanus (surface fish), by CRISPR/Cas9 technology. Homozygote mao knockout larvae died at 13 days post-fertilization. Through a time-course analysis, we report that hypothalamic serotonergic neurons undergo fine and dynamic regulation of serotonin level upon loss of mao function, in contrast to those in the raphe, which showed continuously increased serotonin levels - as expected. Dopaminergic neurons were not affected by mao loss-of-function. At behavioral level, knockout fry showed a transient decrease in locomotion that followed the variations in the hypothalamus serotonin neuronal levels. Finally, we discovered a drastic effect of mao knockout on brain progenitors proliferation in the telencephalon and hypothalamus, including a reduction in the number of proliferative cells and an increase of the cell cycle length. Altogether, our results show that MAO has multiple and varied effects on Astyanax mexicanus brain development. Mostly, they bring novel support to the idea that serotonergic neurons in the hypothalamus and raphe of the fish brain are different in nature and identity, and they unravel a link between monoaminergic homeostasis and brain growth.

Cytoprotective effect of propolis on heat stress induces alteration to histological, ultrastructural, and oxidative stress in catfish (Clarias gariepinus)

Our study helps to evaluate the immune response, antioxidative status, and resistance against heat stress (HS) in Clarias gariepinus treated with propolis extraction; the results will contribute to theories of fish physiology and immunity under high-temperature conditions. Forty-five fish were divided into three equal groups: the control, the HS group at 36 °C, and the HS treated with alcoholic extraction of propolis that dissolved in water for 3 weeks. The results of our study suggested that the stress response differs among tissues thymus, spleen, and liver. All the tissues showed alteration in morphological and cytological structure at the light microscope (LM) and transmission electron microscope (TEM); thymus showed edema and thymocyte destruction; the spleen detected collagen deposition, and the liver displayed endoplasmic reticulum amplification (ER). In addition, we examined oxidative stress and antioxidant defenses (lipid peroxidation, catalase, and glutathione) of the spleen and measured blood biochemical parameters (alanine transaminase and aspartic transaminase levels) after heat stress. However, this toxic effect of HS was neutralized by the propolis extraction. To conclude, propolis is recommended to cope with the impacts of heat stress on catfish (Clarias gariepinus) by improving immunity and antioxidative resistance.