Predatory Fish Research Articles

Fish–Seascape Associations Within an Offshore Protected Area in the Arabian Gulf

ABSTRACTCoral reef ecosystems support high fish biodiversity through ecological interactions with structural complexity across multiple spatial scales including coral colony architecture and the surrounding seascape structure. In an era where the complexity of coral reef ecosystems is being diminished, understanding the importance of structural characteristics beyond single focal patches has the potential to better inform actions for protecting, restoring or creating habitat for reef‐associated species. A seascape ecology approach was applied to explore the associations between multiple scales of seascape structure and fish assemblage response variables within a small (49.6 km2) offshore no‐take MPA, Sir Bu Nair Island Protected Area, in Sharjah, United Arab Emirates. Fish–seascape associations were modelled with single regression trees. Both in situ and remote sensing–derived variables produced the best models with highest contributions from coral cover, amount of hard‐bottom habitat type and structural complexity of the seafloor terrain. Fish species richness was significantly higher where coral cover exceeded 35%. The hard‐bottom areas with coral supported diverse assemblages dominated by carnivorous and omnivorous fishes. The Sir Bu Nair Island Protected Area provides a critical refuge for threatened and regionally overexploited species including those with low resilience to fishing. The ecological success of this protected area is key to safeguarding regional marine biodiversity and recovering fish populations to enhance food security.

Adaptation in the Anthropocene: How behavioural choice and colour change enables chameleon prawns to camouflage on non-native seaweeds.

Animals combine colour change and behavioural choices to enhance concealment and adapt to changes in habitat in time and space. However, non-native and invasive habitat-forming plants and seaweeds can change the landscape, challenging animals to remain camouflaged, especially when the colour of the new habitat differs from the native backgrounds.The chameleon prawn (Hippolyte varians) exhibits remarkable colour variation and effective camouflage against different native seaweeds in shallow tidepools. Individuals optimize crypsis by choosing colour-matching seaweeds and changing colour over time. In some locations, the prawn's native habitats are now replaced by non-native seaweeds of different coloration and structure, making it important to understand whether substrate choice and colour change facilitates the occupation of these seaweeds and enables prawns to camouflage against new backgrounds.Using image analysis and visual modelling of a fish predator, we assessed the colour variation and camouflage of chameleon prawns occupying the non-native seaweeds brown wireweed (Sargassum muticum) and pink harpoon weed (Asparagopsis armata) in southwest UK. We performed laboratory trials to examine whether prawns maintain their preference for colour-matching native substrates when given a choice between them and non-native seaweeds, and if they can change their coloration to improve camouflage against non-native substrates.Prawns exhibit phenotypic diversity and camouflage that varied with the non-native seaweed species, with low colour variation and effective camouflage on pink harpoon weed, but high colour diversity and reduced concealment against brown wireweed. Prawns choose non-native seaweeds when the alternative native substrate provides mismatching coloration, but they did not exhibit any preference between colour-matching native and non-native seaweeds. Once in non-native habitats, prawns change their appearance over a few days to match the background, sometimes faster than when changing on native seaweeds of contrasting coloration.Although human activities considerably modify the coloration of marine landscapes by increasing the establishment of non-native seaweeds, the impacts of those changes appear less severe for colour-changing species, such as chameleon prawns, and will depend on the similarity between the colour of the new substrates and the original native backgrounds, and how animals use behaviour and physiology to match new habitats.

Assessing the use of remote underwater video (RUV) to identify fish and their feeding behaviour in New Zealand's Greenshell™ mussel (Perna canaliculus) farms

Fish predation poses a significant and escalating challenge for the global mussel aquaculture industry. In New Zealand, Greenshell™ mussel farms experience crop losses of up to 100 % that are anecdotally attributed to fish predation, although the fish species responsible have not been confirmed. In this study, remote underwater video (RUV) was used to observe fish activity within four mussel farms at different stages of production in the Firth of Thames, New Zealand. The RUV enabled the identification of the fish species inhabiting mussel farms, including those responsible for predating cultured mussels. Four fish species were identified as frequent inhabitants of the mussel farms, with Australasian snapper (Chrysophrys auratus) and parore (Girella tricuspidata) the most abundant at three out of four mussel farm sites. Australasian snapper was the most common predator, taking as many as 2880 bites of the dropper lines holding mussels in a single 11 min 47 s video recording. Snapper formed feeding aggregations around dropper lines holding juvenile mussels (> 20 mm SL), indicating their potential to remove mussels from nursery farms in a short amount of time. Observations of the feeding behaviour of parore indicated their potential to contribute to the losses of mussels on recently seeded spat farms with these fish recorded tearing apart seeded lines, possibly targeting the macroalgae that is seeded out with the mussel spat. Besides confirming the identity and the predatory behaviour of fish species that are contributing to crop losses from mussel farms in New Zealand, this study also confirms the effectiveness of RUV methods for this purpose. This knowledge can be used to begin to develop mitigation strategies aimed at reducing crop losses in mussel aquaculture.

The impact of microplastics on lake communities: A mesocosm study

Plastics are pervasive pollutants that are being produced at an increasing rate to meet consumer demands. After entering the environment, plastics can break down, creating smaller fragments, including secondary microplastics. Microplastic contamination in lakes has been recorded worldwide, and the ingestion of microplastics has been documented in zooplankton, macroinvertebrates, and fish. Microplastic ingestion and exposure can cause varying deleterious effects on these organism groups, but the impact of realistic microplastic concentrations on whole freshwater food webs requires further study. We addressed these knowledge gaps by conducting an 8-week experiment factorially crossing microplastic addition at a concentration of 1.5 particles/L with a fish predator (perch, Perca fluviatilus) presence in 1200-L outdoor mesocosms. Microplastic exposure had time-varying effects on zooplankton abundance, with a lower abundance of zooplankton in plastic treatments at the end of the experiment. Although microplastics had no impact on total macroinvertebrate abundance, there were effects on individual taxa. In the presence of microplastics, the cased caddisfly Triplectides spp. had a significantly lower abundance, which may have led to an increase in the snail Gyraulus spp. in week eight. Across the benthic and pelagic invertebrate communities, there were near-significant compositional differences between control and plastic treatments. These findings indicate that microplastic exposure may negatively impact freshwater invertebrate communities, even at low, field-realistic concentrations representative of the densities currently found in lakes.

Predator Personality Variation, Not the Multiple Stressors of Temperature and Light, Determines Feeding Motivation in an Ambush Piscivore Saxatilia proteus

ABSTRACTEnvironmental conditions in freshwater ecosystems are increasingly determined by human activity. Increased temperature and light intensity are among the anthropogenic stressors dramatically altering these ecosystems, for example, through deforestation that reduces canopy cover of riparian vegetation. Simultaneous exposure to multiple stressors complicates predictions of responses to environmental stressors due to potential interactions, yet the interaction between temperature and light intensity on feeding motivation remains poorly understood. Here, a fully factorial design was employed to investigate the combined effect of increased temperature and light intensity on the feeding motivation of a freshwater predator, the pike cichlid Saxatilia proteus. Strikes toward food items were used to quantify the subjects' motivation to feed. We found no effect of temperature or light intensity on feeding motivation, either individually or as an interaction. Our repeated measures design allowed us to test whether the predatory fish showed personality variation, i.e., consistent inter‐individual differences, in their motivation to feed. While the time taken to make the first strike was not consistently different between individuals, the number of strikes in 1 min, 3 min and the time taken for the 10th strike (which were strongly correlated to one another) was consistently different between individuals. This variation could not be explained by variation in body length, which had no effect as a main effect. Thus, we suggest that anthropogenic effects that alter the composition of individuals in a population of predators, for example selective harvesting, will have a greater ecological effect than direct short‐term effects of variability in environmental factors.

Benthic Pond Macroinvertebrates Coexist with Nearby Potentially Predatory Fish

Benthic Pond Macroinvertebrates Coexist with Nearby Potentially Predatory Fish

The impact of increasing turbidity on the predator–prey interactions of freshwater fishes

Abstract Human activities are exacerbating environmental change globally. Turbidity in freshwater systems is increasing due to extreme weather events and intensification of activities such as deforestation, urbanisation, agriculture and altering water flow with dams and other structures. Prey species may benefit from turbid habitats as turbidity creates a visual barrier to predators; such predators thus face reduced foraging success as water clarity decreases. However, the literature on the effects of water turbidity on predator–prey interactions in fish is often contrasting. Environmentally driven changes in predator and prey behaviour, foraging and survival ultimately have the potential to affect community structure and ecosystem functioning, thus understanding the impact of changes in turbidity on predator–prey interactions should be a priority. Given the contrasting results in the primary literature, the aim of this review is to provide a broad overview of the current knowledge on the impacts of increased turbidity on predator–prey interactions in freshwater fishes, summarise the published literature and identify knowledge gaps on this topic. We collated 281 studies from the peer‐reviewed literature that tested the impact of water turbidity on the foraging behaviour of predatory fish and anti‐predator behaviour of prey fish. We recorded changes in predator and prey behaviours in response to changes in turbidity levels. Furthermore, we reported whether these behavioural changes were considered to have a positive (e.g. enhanced foraging success) or negative (e.g. higher mortality) impact on the focal species, or whether the impact was unspecified (e.g. changes in anti‐predator behaviour without quantifying actual predation risk). The literature has some strong taxonomic, geographical and environmental biases, where most research focused on commercially important, temperate species. A large proportion of studies (47%) reported a negative (versus a positive or unspecified) impact of turbidity on the focal species (either predator or prey freshwater fish). Negative impacts were reported more often for predators (58%) compared to prey (19%) and while changes in behaviour were frequently reported in prey species, if these changes are adaptive or not is unclear, as actual predation risk was not assessed in the majority of relevant studies (55%). Increases in turbidity have complex effects on predator–prey interactions, with negative impacts more often reported for adult piscivore predators, while prey species may gain a relative advantage compared to visual predators. However, whether prey behavioural responses to increased turbidity are adaptive is generally unclear. We suggest that a more holistic and ecologically relevant experimental approach is needed to disentangle the underlying mechanisms and determine the adaptive nature of prey behavioural responses to increased turbidity. Our review serves as a broad and comprehensive summary of the empirical research conducted on impacts of increasing water turbidity on predator–prey interactions in freshwater fishes. It highlights knowledge gaps and provides a reference point to guide future experimentation and research synthesis in this crucial and growing area of research.

Lake Restoration Improved Ecosystem Maturity Through Regime Shifts—A Case Study of Lake Baiyangdian, China

Lake ecosystems are impacted by anthropogenic disturbances and have become vulnerable worldwide. Highly disturbed lake ecosystems are not well understood due to the lack of data on changes in the structures and functions of ecosystems. In this paper, we focus on Lake Baiyangdian (BYDL), the largest shallow lake in North China. Following the establishment of the Xiong’an New Area (XNA) in 2017, concerted efforts to restore BYDL’s aquatic environment have been undertaken, which has led to significant changes in the structures and functions of the ecosystems. We evaluated the biomass dynamics of main biological communities and detected the regime shifts of environmental factors in BYDL from 2016 to 2023. Further, we constructed a food web model for the BYDL ecosystem in 2023 by using Ecopath with Ecosim (EwE) and made a comparison with the reported results in 2018. The results showed significant changes in the ecosystem structure of BYDL over the last 6 years. In 2023, the submerged macrophytes biomass in the system increased by 4.2 times compared to 2018, leading to an increase in total system throughput. We found that BYDL changed from an algal-type lake to a macrophyte-dominated lake. In addition, we found TN, NH4+-N, and CODMn were significantly decreased in BYDL during the restoration. TN and NH4+-N had a change point in approximately 2021, indicating that a regime shift had occurred during restoration. Overall, the BYDL ecosystem was in an immature but developing state, as indicated by ecological network analysis indicators. Nutrient-loading reduction, hydrological regulation, and rational biomanipulation may be the potential driving factors of change in the BYDL ecosystem. We strongly recommend the timely harvesting of submerged macrophytes, the proliferation and release of herbivorous fishes, and the assessment of the ecological capacity of carnivorous fishes in the future ecological restoration of BYDL.

Rapid predator-prey balance shift follows critical-population-density transmission between cod (Gadus morhua) and capelin (Mallotus villosus)

Sensing limitations have impeded knowledge about how individual predator-prey interactions build to organized multi-species group behaviour across an ecosystem. Population densities of overlapping interacting oceanic fish predator and prey species, however, can be instantaneously distinguished and quantified from roughly the elemental individual to spatial scales spanning thousands of square kilometres by wide-area multispectral underwater-acoustic sensing, as shown here. This enables fundamental mechanisms behind large-scale ordered predator-prey interactions to be investigated. Critical population densities that transition random individual behaviour to ordered group behaviour are found to rapidly propagate to form vast adversarial prey and predator shoals of capelin and surrounding cod in the Barents Sea Arctic ecosystem for these keystone species. This leads to a sudden major shift in predator-prey balance. Only a small change in local behaviour triggers the shift due to an unstable equilibrium. Such unstable equilibria and associated balance shifts at predation hotspots are often overlooked as blind spots in present ocean ecosystem monitoring and assessment due to use of highly undersampled spatio-temporal sampling methods.

The Box Crab Calappa hepatica as a Nuclear Species for the Opportunistic Foraging Behaviour of the Flowery Flounder, Bothus mancus, in the Indo-Pacific

Some predatory fishes may exhibit opportunistic feeding behaviour by exploiting potential prey that is distracted, displaced, or exposed by the activities of a third party that acts as a ‘nuclear’ species. Other fishes mostly perform the role of ‘nuclear’ species, but benthic invertebrates, such as octopuses, have also been reported. Crabs are rarely observed in this role, with only a few records from the tropical Atlantic Ocean. Here, we report the temporary association between two specimens of the flowery flounder, Bothus mancus (family Bothidae), and a box crab, Calappa hepatica (family Calappidae), from the Philippines, representing the first record of a crab–fish feeding association in the Indo-Pacific region.

Faecal DNA Metabarcoding for Diet Analysis of Endangered Fish Species, Odontobutis obscurus.

Understanding the ecological characteristics of endangered species is essential for their management and conservation. The dark sleeper (Odontobutis obscurus) is a carnivorous freshwater fish that has been designated an endangered species in South Korea because of its highly restricted habitat range and small population size. However, ecological research on prey items for this species remains severely limited globally, posing challenges for establishing conservation measures such as translocation management. In this study, the food sources and feeding strategies of O. obscurus were identified through non-invasive faecal DNA metabarcoding. A total of 24 O. obscurus specimens were collected from Sanyang Stream on Geoje Island, and faecal DNA was amplified using mitochondrial cytochrome c oxidase I (COI) primer. As a result, 13 prey items were identified, comprising fish and benthic invertebrates. Dietary metrics revealed the overall food composition and major food source of O. obscurus, and the Costello method enabled graphical diet analysis, suggesting that O. obscurus is a generalist, feeding on a wide variety of food sources. The food selectivity index suggested that O. obscurus prefers specific prey items, such as genus Misgurnus, Zacco (fish), Radix (gastropod), and Ephemera (mayfly). This molecular method facilitated the diet analysis of an endangered fish species that cannot undergo dissection, providing crucial information for their management, particularly regarding translocation efforts.

Transcriptome analysis reveals the importance of phototransduction during the first-feeding in mandarin fish (Siniperca chuatsi).

The mandarin fish (Siniperca chuatsi), as a typical freshwater carnivorous fish, has high economic value. Mandarin fish have a peculiar feeding habit of feeding on other live fry during the first-feeding period, while rejecting zooplankton or particulate feed, which may be attributed to the low expression of zooplankton-associated gene sws1 in mandarin fish. The domesticated strain of mandarin fish could feed on Artemia at 3 days post hatching (dph). However, the mechanism of mandarin fish larvae recognize and forage Artemia as food is still unclear. In this study, we employed transcriptional analysis to identify the representative differential pathways between mandarin fish larvae unfed and fed with Artemia at 3 dph. The comparative transcriptome analysis has unveiled a tapestry of genetic expression, highlighting 403 genes that have been up-regulated and 259 that have been down-regulated, all of which constitute the differentially expressed genes (DEGs). KEGG pathway analysis revealed that the number of differentially expressed genes in the photoconductive signaling pathway was the largest. Next, the Vorinostat (suberoylanilide hydroxamic acid, SAHA) was used to assess whether sws1 induced ingestion of Artemia in mandarin fish larvae. We discovered that SAHA-treated larvae had more food intake of Artemia and up-regulated the transcription level of npy, which might have been associated with the up-regulated of sws1 opsin. Additionally, exposure to 0.5 µM SAHA increased the expression of genes involved in phototransduction pathway. These findings would provide insights on the molecular processes involved in mandarin fish larvae feeding on Artemia at the first-feeding stage.

Predicting habitat suitability for the co-occurrence of an estuarine mesopredator and two top predatory fishes

Predicting habitat suitability for the co-occurrence of an estuarine mesopredator and two top predatory fishes

Histochemical Analysis of DNA and RNA Identified by Methyl Green - Pyronin ‘Y’ Method and Feulgen’s Reaction Staining in Liver of Channa Punctatus

The light microscopy was to identify cells, storage products, tissue deposits, and microbial pathogens. The Assessment of surrounding tissue with special stains may reveal aspects of interest for the tissue. We illustrate the expected staining characteristics of control Channa punctatus liver tissue with Methyl Green -Pyronin ‘Y’ and Feulgen’s Reaction stains. The aim of this study was to characterize the normal structure of the liver of Channa punctatus, a carnivorous freshwater fish found in Hasanparthy Lake, using gross anatomy, histology and histochemistry. Anatomically, the liver presents C-shaped and only two lobes smaller right and bigger left. The gallbladder is located in right lobe and shows elongated shaped. Histological analysis demonstrated that the hepatic parenchyma is made of two hepatocytes plates surrounded by sinusoids. The fish moreover pancreatic tissue was observed in visceral portion of liver, formed by exocrine pancreatic tissue and islet organ, constituting an extrahepatic pancreas. The nucleic acids content in different tissues in the freshwater fish of Channa punctatus. The fish were scarified and the tissues such as liver and Pancreas removed and processed for determination of nucleic acids. The results obtained in the present study may provide a contribution to the knowledge of the characteristics of nucleic acid as parameters of estimation of DNA and RNA levels in Liver of the fish.

Assessment of heavy metal concentration in pelagic fish species and associated health risks along the Kanyakumari coast, India – a baseline study

ABSTRACT This research examines heavy metal concentration in fish from the Kanyakumari coast of India, emphasising its ecological consequences and possible health hazards for consumers. The study investigates the levels of several heavy metals such as zinc, manganese, iron, cadmium, copper, chromium, cobalt, lead, and nickel in different organs of multiple pelagic fish species obtained from the Kanyakumari fish landing site. Concentrations of heavy metals exhibit considerable variation among different fish organs and species, with distinct patterns identified for each metal. Muscle tissue often demonstrates reduced amounts of heavy metals in comparison to other organs. Except Zn and Fe, other heavy metals in fish muscle were above the acceptable limits set by health organisations. Cadmium was found to be 36-fold higher than the permissible limit, followed by nickel (30.4) and lead (7.6). Copper, nickel, and cadmium provide possible health hazards according to the Target Hazard Quotient (THQ). Lead and cadmium exhibit Excessive Lifetime Cancer Risk (ELCR) markedly above tolerable thresholds. Large predatory fish, such as Thunnus thynnus, exhibit elevated levels of contaminants such as cadmium. Environmental conditions, aquatic habitat, and dietary intake affect metal build-up in fish. The research employs multiple analytical methods and statistical methods, such as Atomic Absorption Spectrophotometry, correlation and Principal Component Analysis, to evaluate heavy metal concentrations and their interrelations. The study underscores the critical necessity for monitoring and mitigation techniques to combat heavy metal pollution in coastal waters and its possible effects on human health through fish intake.

Food Preference of Purple‐Spotted Bigeye (Priacanthus tayenus Richardson 1846) in Northern Coast of Java, Indonesia

ABSTRACTDiet is one of the essential information used in the management of fisheries resource. The objective of this study was to assess the dietary preferences, index of preponderance, trophic level, food niche breadth, and food overlap of purple‐spotted bigeye (Priacanthus tayenus) caught from the northern coast of Java, Indonesia. A total of 407 fish samples were collected from July to October 2023. Each fish sample was measured for total length and body weight. Fish were then dissected to determine sex, gut length, gut volume, and diet composition. Data analysis included relative gut length, diet composition, frequency of occurrence, trophic level, index of preponderance, food niche breadth, and food overlap. The result showed that the purple‐spotted bigeye is a carnivorous fish (trophic level ranges from 3.88 to 4.18), whose main food is fish and shrimp. Based on the niche breadth value, purple‐spotted bigeye from East Java were more diverse in finding food (niche breadth = 0.26) than from West Java (niche breadth = 0.06) and Central Java (niche breadth = 0.09). The purple‐spotted bigeye species from West Java and Central Java exhibited a high level of competition in their search for food, as indicated by a food overlap value of 0.998.

Seasonal Distribution of Key Small-Sized Fish in the South Inshore of Zhejiang, China

Small-sized fish are a vital food source for large predatory commercial fish and play a key role in marine food webs, bridging lower and higher trophic levels. They are indispensable in maintaining the energy flow and material cycling within aquatic ecosystems. This study utilized bottom-trawl survey data from 2017 to 2020 along the south inshore of Zhejiang, China, complemented by concurrent environmental data, to examine the influence of environmental factors on the resource density and seasonal distribution patterns of four dominant small-sized fish species. The research findings indicated that SSH (sea surface height) and Chl (chlorophyll-a concentration) emerged as the key environmental factors influencing resource densities, with all four species exhibiting similar preferences toward these variables. However, significant disparities were observed in their preferences for SST (sea surface temperature), SSS (sea surface salinity), and DO (dissolved oxygen). The various species’ resource density and distribution patterns underwent significant seasonal variations. Additionally, the seasons and regions with the highest resource densities consistently aligned, occurring predominantly in autumn within the northern waters of the study area. This research further elucidated the environmental predilections and seasonal spatial distribution traits of small-sized fish in the south inshore of Zhejiang, an important feeding ground for economic fish species in the East China Sea. This provides scientific backing for forecasting alterations in coastal fishery resources under environmental and climate change scenarios and supports ecosystem-based fisheries management strategies.

Prey diversity in the deep ocean: metabarcoding feeding ecology of the commercially important queen snapper in the US Caribbean

The queen snapper, Etelis oculatus, is experiencing a growing fishery presence across the wider Caribbean, yet our understanding of its distribution, biology, and ecology remains limited. To address this gap, we investigated the feeding ecology of this demersal deep-water snapper using two molecular approaches: single-species barcoding and multispecies metabarcoding. Between November 2019 and July 2020, we collected 157 queen snapper from seven locations along the west coast of Puerto Rico. Our analysis identified a diverse array of prey items in the stomachs, comprising 61 species from 31 families, 18 orders, and 38 genera. Our findings suggest that E. oculatus is a large carnivore, primarily preying on squids, shrimps, and deep-water fishes. Notably, common fish prey included Diaphus brachycephalus, D. dumerilii, Dasyscopelus selenops, Coccorella atlantica, Sigmops elongatus, and Zaphotias pedaliotus. In contrast, prevalent invertebrate prey consisted of Abralia veranyi, Doryteuthis pealeii, Abralia redfieldi, Oplophorus gracilirostris, and Systellaspis debilis. Although our data suggest potential variation in diet composition across locations, definitive conclusions remain elusive. However, we observed heightened prey richness at seamount Pichincho, possibly attributable to the high structural complexity of the karst terrain on the seafloor. Additionally, we noted variation in prey species composition across size classes, with certain species more prevalent in larger or smaller queen snapper. Given the challenge of examining the prey of deep-water fish species, our study showcases the utility of both single-species barcoding and multispecies metabarcoding methodologies in characterizing the dietary range of queen snapper and similar demersal deep-water carnivorous fishes. The multispecies metabarcoding approach, in particular, offers a rapid, comprehensive, and effective means of identifying prey species. As the commercial value of the queen snapper continues to rise, our investigation into its feeding behavior provides critical baseline information for future species management efforts. By enhancing our understanding of its ecological dynamics, we aim to contribute to informed conservation and sustainable fisheries practices in the region.

Fibroblast growth factor 1 (FGF1) improves glucose homeostasis, modulates gut microbial composition, and reduces inflammatory responses in rainbow trout (Oncorhynchus mykiss) fed a high-fat diet

High-fat diets (HFDs) are widely used in aquaculture due to their lipid and protein-conserving effects, thereby reducing feed costs. However, prolonged feeding of HFD often leads to metabolic disorders in fish, such as disruption of hepatic lipid homeostasis, liver injury, and disruption of glucose homeostasis. Fibroblast growth factor 1 (FGF1) plays an essential role in controlling glucose levels in the body and dampening immune reactions. However, its impact on teleosts remains poorly researched. The therapeutic potential of recombinant FGF1 (rFGF1) was examined in a 6-week culture experiment involving rainbow trout (Oncorhynchus mykiss) that were fed an HFD. The results revealed that rFGF1 significantly reduced serum glucose levels and hepatic PEPCK and G6PC activities, but improved hepatic glycogen (P < 0.05), compared to the HFD + PBS group. Further experiments indicated that the inhibitory effect of rFGF1 on hepatic gluconeogenesis was mediated by the cAMP signaling pathway and was dependent on the high expression of PDE4D. In addition, rFGF1 increased hepatic glycogen content, which involves the AKT-GSK3β axis. Despite this increase, rFGF1 did not lead to glycogen storage disease, as shown by reduced hepatic inflammation as a result of decreased GOT (glutamic oxaloacetic transaminase), GPT (glutamic pyruvic transaminase), and elevated SOD (superoxide dismutase) in the rFGF1-treated group, accompanied by decreased il-1β, il-6, and xbp-1, and elevated nrf2 and number of hepatocyte autophagosomes. Alterations in gut microbes and short-chain fatty acids (SCFAs) were noted, indicating that rFGF1 caused a notable rise in intestinal Lactobacillus, acetic acid, and butyric acid levels. This study investigated the molecular mechanisms of rFGF1 on glucose metabolism and inflammatory responses in an HFD-fed rainbow trout model, providing new insights to improve the regulation of glucose metabolism in carnivorous fish.

The influence of food web structure and foraging behaviour on visual system traits in a predatory freshwater fish

Lake trout (Salvelinus namaycush Walbaum, 1792) forages across macrohabitats (offshore vs nearshore) that likely pose different challenges to the visual system. We examined how differential foraging between macrohabitats challenges the visual system by sampling lake trout from four lakes with differing food web structures (e.g., presence/absence of cisco/smallmouth bass) and evaluating the association between nearshore energy use and visual traits. We found that lake trout foraging more nearshore had relatively larger eyes (corrected for body size) and larger optic tectum size only in lakes with the large pelagic cisco prey absent, while there was no association with these visual traits when cisco was present. Eye shape was not influenced by nearshore foraging. Our results suggest that nearshore foraging challenges the visual system more than offshore foraging but that this may be dependent on important food web structural attributes.