Feeding Ecology Of Fishes Research Articles

Insight into the diet of early stages of mesopelagic fishes in the Indian Ocean using DNA metabarcoding

Despite playing a critical role in oligotrophic ocean food webs, relatively little is known about the diet of mesopelagic fishes in the Indian Ocean. These fishes are an abundant component of the micronekton assemblages and are a major energy- and nutrient-rich food source, linking the plankton which they feed on to marine predators at higher trophic levels. DNA metabarcoding, a molecular method to identify species from mixed assemblages, has not been commonly used in studies of mesopelagic fish diet, but using it to analyse gut contents can greatly improve the understanding of mesopelagic fish feeding ecology. In this study, we apply DNA metabarcoding (18S rRNA and COI) to gut contents from Stomiiformes and Myctophiformes species from 20 sampling stations covering 30 ˚ of latitude on the 110 ˚ E meridian in the Indian Ocean. In total, 174 fish specimens from 13 genera were examined. Differences in the gut contents among fish families, geographic areas and fish stages were identified. Specimens within the family Myctophidae had the most diverse diet, more so in the northern sampling stations than the south. Gonostomatidae had the least diverse diet. Overall, the most frequently identified prey items from the gut contents were calanoid copepods and halocyprid ostracods. The proportion of halocyprids were also identified to be significantly different among Myctophidae larvae and juvenile specimens, which is a potential ontogenic shift in diet towards a higher ostracod contribution in juveniles as mouth gape increases. In comparison with other plankton abundance data, Copepoda were the most abundant plankton in the gut contents of all fishes sampled throughout the latitudinal gradient, allowing them to be a potential food resource through the region. There are indications that other less abundant plankton, such as like Ostracoda and Malacostraca, may be preferentially targeted by some mesopelagic fish families.

Feeding ecology of Chaeturichthys stigmatias during autumn in Haizhou Bay

Research about feeding ecology of fish is important to understand individual behavior and population development, which is also the basic to analyze trophic structure and function of aquatic ecosystems. Chaetrichthys stigmatias is one of the key species in the Haizhou Bay fisheries ecosystem, which has critical ecological niche within the food web. In this study, we collected samples through bottom trawl surveys during the fall of 2018 in the Haizhou Bay, and analyzed the feeding ecology of C. stigmatias based on both stomach content analysis and stable isotope technology. The results showed that the primary diet groups for C. stigmatias were Ophiuroidea and Shrimp, including Ophiothrix marenzelleri, Ophiopholis mirabilis, Ophiura sarsii, Penaeidae, and Alpheus japonicus. The range of δ13C values of C. stigmatias was from -19.39‰ to -15.74‰, with an average value of (-18.07±0.87)‰, which had no significant correlation with body length. The range of δ15N values was from 8.16‰ to 12.86‰, with an average value of (10.14±1.51)‰, which was positively correlated with body length. The trophic level of C. stigmatias showed a positive relationship with body length, with an average value of (3.74±0.34) and a range value of 3.32 to 4.20 among different size groups. The contribution rates of different prey groups varied significantly. Based on the structural equation modeling, we found that the feeding intensity of C. stigmatias was primally influenced by body length, sea bottom salinity, sea bottom temperature, and water depth, with a particularly signi-ficant positive correlation with body length. The combination of stable isotope technology and stomach content analysis methods could contribute to comprehensive understanding on the feeding ecology of C. stigmatias, providing essential data and foundation for research on trophic structures and resource conservation in the Haizhou Bay ecosystem.

Po-210 activity concentrations in wild and farmed fish from the Aegean Sea and Sea of Marmara and dose assessment to consumers.

Polonium (210Po) is the major contributor (with approximately 90%) to the radiation dose from radionuclides contained in the human diet, and it is mostly associated with seafood. This study presents 210Po activity concentrations in the tissues of 16 fish species from the Aegean Sea and Sea of Marmara. Among all species investigated, the highest 210Po activity concentration was 4450 ± 33 Bq kg-1 dry weight (dw) in the digestive tract of anchovy (Engraulis encrasicolus), and the lowest 210Po activity concentration was 1.3 ± 0.6 Bq kg-1 (dw) in the muscle tissue of the thornback ray (Raja clavata). Significant differences in 210Po concentrations were consistently found among the tissues of fish (P < 0.05). In general, the prominent accumulation of 210Po was observed in the digestive tract and liver while the muscle tissue generally displayed the lower concentrations. Polonium concentrations in the internal organs, such as muscle and liver, were related to the feeding ecology of fish and thus are a consequence of 210Po transfer in the food chain rather than 210Po uptake from water. The average 210Po concentration in fish filet was 54.1 Bq kg-1 dw and to attain the recommended limit for the annual committed effective dose (1 mSv year-1) would require the consumption of 1024 kg of mixed fish filet in 1 year, which is unlikely to happen. The highest 210Po activity concentration in the edible part of fish (filet) was determined in the anchovy (E. encrasicolus) but to reach the 1mSv year-1 limit would require still the consumption of 7.1 kg year-1 of anchovy filet. Similar size specimens of wild and farmed fish, Dicentrarchus labrax and Sparus aurata, were analyzed to assess the differences in 210Po concentrations. Polonium concentrations in the wild fish were several-fold higher than in farmed specimens, these ones fed with fish feed with 210Po content lower than natural food in the sea. Therefore, the current trend of increasing the consumption of seafood from aquaculture seems to be reducing the radiation exposure to 210Po in the human diet that is considered beneficial to public health.

Fatty acid isotopic composition in Atlantic pollock is not influenced by environmentally relevant dietary fat concentrations.

The application of fatty acid (FA) isotopic analysis has great potential in elucidating food web structure, but it has not experienced the same wide-spread use as amino acid isotopic analyses. The failure to adopt FA isotopic methods is almost certainly linked to a lack of reliable information on trophic fractionation of FA, particularly in higher predators. In this work, we attempt to address this shortfall, through comparison of FA δ13C values in captive Atlantic pollock (Pollachius virens) liver and their known diets. Since catabolism is likely the main cause of fractionation and it may vary with dietary fat content, we investigated the impact of dietary fat concentration on isotopic discrimination in FA. We fed Atlantic pollock three formulated diets with similar FA isotopic compositions but different fat concentrations (5-9% of diet), representative of the range found in natural prey, for 20weeks. At the conclusion of the study, δ13C values of liver FA were very similar to the FA within the corresponding diets, with most discrimination factors < 1. For all FA except 22:6n-3, dietary fat had no effect on discrimination factors. Only for 22:6n-3 did fish fed the highest fat diet have lower δ13C values than the diet consumed. Thus, these FA-specific discrimination factors can be applied to evaluate diets in marine fish consuming natural diets and will serve as additional and valuable biomarkers in fish feeding ecology.

Feeding Ecology of Fishes – A Mini Review

Fishes constitute more than half of the vertebrates, inhabiting almost every aquatic habitat of the world and form an inexpensive source of vital nutrients. The depletion of fishery stocks as a result of anthropogenic interferences is evident worldwide and mandates an urgent need to address the cause before rate of loss exceeds the limit. This makes the assessment of various aspects of fish, especially their feeding ecology quite imperative for developing conservation and management strategies. Food forms a vital factor for fishes required chiefly for growth and reproduction in fishes and its qualitative or quantitative variation is influenced by various biotic and abiotic factors. Amongst the various attributes influencing fishes, food and feeding constitute a vital aspect that impacts the growth and general wellbeing of the fish. Feeding ecology of a fish is directly linked to its population dynamics and helps in understanding of various aspects of fish like habitat preference, competition, prey selectivity, energy transfer etc. Under this backdrop the current review was drafted to acquire knowledge about the three major aspects of feeding ecology of fish i.e., analysis of the gut contents, feeding biology and prey selectivity. The analysis of gut contents helps to identify the prey diversity and abundance consumed by a fish. Feeding biology helps to evaluate the acceptability of the prey by depicting the correlation between biology of the fish and its food preferences. Prey selectivity deals with the evaluation of prey choice depicting the reason behind choice of one prey over the other.

Effect of Artificial Reefs on the Alimentary Strategies of Two Mediterranean Sea Teleosts

In this study, we aimed to investigate the presence of an alteration in the feeding ecology of fish after the deployment of anti-trawling reefs at the Punta Tramontana site (Sardinia, Italy). To achieve this aim, we examined prey in the stomach contents of two target species of fish: Diplodus annularis and Mullus surmuletus. The samples were obtained from fishing activities carried out over one year from June 2017 to October 2018 at two impact sites, selected by the presence of artificial reefs, and two control sites. The results showed that installing these artificial devices increased the food spectrum availability of the target species and induced two different ecological feeding behaviors, probably derived from their different ecologies. D. annularis changed its alimentary strategy from generalist at control sites to specialist at impact sites, focusing its diet on the crustacean Gnathia maxillaris. Mullus surmuletus was not affected by the presence of the barriers, which constitute an additional site where the fish feed during their foraging activities. In conclusion, these anti-trawling reefs, in addition to the purpose for which they are designed (in this case, avoiding illegal trawling), did not produce any negative environmental impact on surrounding marine biota.

Exploring temporal patterns in fish feeding ecology: Are ontogenetic dietary shifts stable over time?

Disentangling the causes and consequences of ontogenetic niche shifts has been a pivotal challenge in ecology, aiming to enhance the understanding of biological processes that function at the individual, population, and community levels. Studies on ontogenetic dietary shifts have traditionally focused on short time scales, mostly including sampling covering just one or a few consecutive years, thus neglecting possible aspects of temporal variation and ecosystem stability that can only be revealed on long-term scales. We address ontogenetic dietary shifts of two fish predators in an intraguild system (Arctic charr and brown trout) using a long-term dataset spanning 20 consecutive years. Our study revealed distinct ontogenetic niche shifts of the two intraguild predators and demonstrated that these patterns were stable over time, suggesting large stability in prey acquisition and resource partitioning despite changes in their abundances and relative species composition. Some interannual variation was observed, but this was primarily due to sampling bias from low observation numbers for some ontogenetic stages, reflecting a common methodical challenge for ontogenetic niche shift studies. The persistent patterns in the trophic ontogeny of intraguild predators likely facilitate population and community stability by reducing inter- and/or intraspecific competition, thereby having important consequences for ecosystem functioning and resilience. Our study provides a strong rationale for performing ontogenetic niche shift studies over several consecutive years, enabling important insights into temporal variation, enhancement of observation numbers by merging data from multiple years, and the facilitation of a less intrusive sampling scheme for more vulnerable populations.

Are fatty acids in fish the evidence of trophic links? A case study from the southern Baltic Vistula Lagoon

Most knowledge on the feeding ecology of fish has been based on the analyses of food remains from the alimentary tracks. This traditional method, however, only provides information about recently consumed food, and is burdened with a risk of incorrect assessment of the role of individual diet components due to the different rates of digestion. A method free from such limitations is the analysis of fatty acids. The objective of our study was to recognise the potential of fatty acid signatures in providing information on the diet and feeding habits of six fish species from the shallow brackish Vistula Lagoon, southern Baltic Sea (Anguilla anguilla, Abramis brama, Rutilus rutilus, Pelecus cultratus, Perca fluviatilis, Sander lucioperca). Multivariate statistical analyses of fatty acid signatures permitted relevant grouping of the fish according to species and their diet, as well as evidenced substantial ontogenetic changes in perch, roach, and bream. They might be caused by dietary changes but can also result from internal regulatory processes. The obtained results confirmed that fatty acids provide useful, time-integrated dietary information, contributing to expanding knowledge regarding the feeding ecology of fish in shallow coastal water ecosystems. They also pointed to the necessity of assessment of the invertebrates and fish's ability to perform endogenous synthesis of polyunsaturated fatty acids, particularly in research on benthic communities. To our best knowledge, this is the first attempt to investigate the feeding habits of fish and food-web relationships in the coastal waters of the Baltic Sea using fatty acids.

Feeding habit and diet composition of Glossogobius aureus Akihito & Meguro, 1975 in the Vietnamese Mekong Delta

Glossogobius aureus (Gobiiformes: Gobiidae) is a target fish and widely distributed in the Mekong Delta, from fresh to brackish waters. However, knowledge on its food and feeding ecology is scarce. Therefore, this research was carried out in four sampling sites along the estuarine of Hau River in order to fill this information gap. A total of 742 individual fish was collected monthly using trawl nets from January to December 2020. A combined analysis of the fullness index and Costello graph suggested that this fish species displayed high feeding intensity. The results revealed that G. aureus is a carnivore and its food composition comprised Acetes spp., Actinopterygii, zooplankton, and other preys (e.g. snails and detritus). Acetes spp. is the main food of this species. The diet composition varied with sites but not genders, fish sizes, and seasons. Acetes spp., Actinopterygii and other preys contributed to the spatial variation of food composition. The findings revealed knowledge about the fish feeding ecology, which may propose suitable foods for its aquaculture development.

Foraging ecology of the amphibious mudskipper Periophthalmus chrysospilos (Gobiiformes: Gobiidae).

The food composition and feeding ecology of fishes living in the intertidal zone play an essential role in understanding the energetic connectivity between terrestrial and aquatic systems. Periophthalmus chrysospilos is an amphibious fish species occurring in the intertidal zone, but data on its diet and foraging ecology is still poorly known. This study on Ps. chrysospilos was carried out from April 2020 to March 2021 at four sites within the Mekong Delta estuary to define the influence of spatio-temporal factors on the diet of this species. The diet composition and relative gut lengths (RGLs) of Ps. chrysospilos were analysed in relation to four parameters—sex, size, site, and season. A total of 1,031 individuals were collected, and their digestive tract lengths were used to calculate the RGL. The digestive tracts of only 546 individuals were with food items (approximately 1:1 of empty vs full digestive tract) and were subsequently used for further analyses. The ranges in total length and weight in both adult and juvenile individuals were 3.4–10.6 cm and 0.38–14.13 g, respectively. The RGL values varied with season, fish size and site, but was always lower than 1, indicating a predominantly carnivorous diet. The variability of food items found within the digestive tracts demonstrated its adaptability in pursuing prey items within the limits of the littoral zone, and its importance as a conduit of terrestrial-marine connectivity. This species is characterised as an opportunistic mesopredator feeding primarily on Acetes spp., Uca spp., Dolichoderus sp., and rarely on Polychaeta and Actinopterygii. Other items found within the digestive tract are Mollusca, and detritus. The diet composition of Ps. chrysospilos did not vary with season and size, but changed with sex and site parameters. Uca spp. contributed to the sexual variation in dietary component, whereas Mollusca, Uca spp., Dolichoderus sp. and detritus, were drivers for spatial variation in the dietary component. The research provides fundamental information on diet composition and feeding strategy, as well as contributes towards knowledge on foraging ecology and resource use by intertidal animal communities.

Do macrophytes act as restaurants for fishes in a tropical beach? An approach using stomach content and prey availability analyses

Tropical sandy beaches have low primary productivity, thus depend on external food sources. Generally, allochthonous macrophytes, form the basis of these food webs, also may influence factors such as fish’s abundance, richness, species composition, and biomass. However, the role of such drifting macrophytes to the feeding ecology of fishes in tropical sandy beaches is uncertain. We aim to explain if this microhabitat acts as restaurants for fishes in a tropical sandy beach by performing stomach content and prey availability analyses using Stellifer punctatissimus as a model because it has an association with drifting macrophytes mainly on sandy beaches along the northeastern Brazilian coast. The most consumed prey was amphipods, which were eaten in a specialist way, especially by the smaller fishes. The prey availability along with electivity index suggested that this species may choose amphipods. Seasonal variations suggest that the fishes did not locate suitable prey as an effect of the availability, this can be also explained by optimal foraging theory and compensatory growth. Here, we redefined the S. punctatissimus trophic guild as zooplanktivorous, highlighting drifting macrophytes as restaurants for fishes in a tropical sandy beach as they are the main source of food.

A Hemimysis-driven novel ecosystem at a modified rubble-mound breakwater: An Engineering With Nature® Demonstration Project.

The US Army Corps of Engineers (USACE) repairs aging breakwater structures as part of routine maintenance to maintain safe navigation in Great Lakes commercial ports. A USACE repair to an existing breakwater structure in Milwaukee Harbor (WI) implementing Engineering With Nature (EWN) principles created complex rocky habitat by strategically placing cobble-sized stone over conventional 5.4 to 9.1 metric ton boulders, thus creating "control" (boulder) and "treatment" (cobble) habitats. We evaluated the resultant nature-based breakwater (NBBW) developing food web versus an adjacent referencesite on the same breakwater and determined that, unexpectedly, locally abundant Hemimysis anomala were impacting the food-web dynamics and feeding ecology of fishes occupying the structure. Fish and forage communities were sampled using gillnets, night scuba diving surveys, rock collections, and a novel trap to capture invertebrates. The resultant NBBW became home to a prolific population of nonindigenous Hemimysis, with indications that they were more abundant on cobble versus boulders,based on rainbow smelt feeding. This lithophilic/cave swelling mysid provided an important new food resource in Milwaukee Harbor for two introduced pelagic prey fishes: alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax). Gillnetting and night scuba diving surveys confirmed that rainbow smelt preferred to forage on the cobble section (p < 0.05). Hemimysis were also the primary food item consumed by nearshore game fishes such as young-of-the-year (YOY) yellow perch (Perca flavescens), YOY largemouth bass (Micropterus salmoides), and juvenile rock bass (Ambloplites rupestris). We propose that those breakwaters that harbor abundant Hemimysis constitute novel ecosystems (ecosystems that include both native and non-native biota) that might benefit harbor fisheries if well-managed. This project demonstrated how a low-cost design modification could be applied during the repair of rubble-mound, breakwater structures to achieve benefits beyond safe navigation. Integr Environ Assess Manag 2022;18:49-62. Published 2021. This article is a US Government work and is in the public domain in the USA.

Feeding studies take guts - critical review and recommendations of methods for stomach contents analysis in fish.

Studies on the feeding ecology of fish are essential for exploring and contrasting trophic interactions and population and community dynamics within and among aquatic ecosystems. In this respect, many different methods have been adopted for the analysis of fish stomach contents. No consensus has, however, been reached for a standardised methodology despite that for several decades there has been an ongoing debate about which methodical approaches that should be preferred. Here, we critically review and scrutinise methods, addressing their strengths and weaknesses and emphasising inherent problems and possible pitfalls in their use. Although our critical assessment reveals that no completely ideal approach exists, appropriate and reliable procedures can be adopted through careful considerations and implementation. In particular, we advocate that different objectives require different methodical approaches and the choice of method should therefore be closely linked to the research questions that are addressed. For a standardisation of methods, we recommend a combination of the relative-fullness and presence-absence methods as the optimal approach for the commonly applied feeding studies addressing relative dietary composition in terms of prey diversity and abundance. Additionally, we recommend the gravimetric method for objectives related to the quantification of food consumption rates and the numerical method for prey selection studies. DNA-based dietary analysis provides a new and promising complementary approach to visual examination of stomach contents, although some technical challenges still exist. The suggested method standardisation facilitates comparisons across species, ecosystems and time and will enhance the applicability and benefits of fish feeding studies in trophic ecology research.

Thyroid hormone modulation during zebrafish development recapitulates evolved diversity in danionin jaw protrusion mechanics.

Protrusile jaws are a highly useful innovation that has been linked to extensive diversification in fish feeding ecology. Jaw protrusion can enhance the performance of multiple functions, such as suction production and capturing elusive prey. Identifying the developmental factors that alter protrusion ability will improve our understanding of fish diversification. In the zebrafish protrusion arises postmetamorphosis. Fish metamorphosis typically includes significant changes in trophic morphology, accompanies a shift in feeding niche and coincides with increased thyroid hormone production. We tested whether thyroid hormone affects the development of zebrafish feeding mechanics. We found that it affected all developmental stages examined, but that effects were most pronounced after metamorphosis. Thyroid hormone levels affected the development of jaw morphology, feeding mechanics, shape variation, and cranial ossification. Adult zebrafish utilize protrusile jaws, but an absence of thyroid hormone impaired development of the premaxillary bone, which is critical to jaw protrusion. Premaxillae from early juvenile zebrafish and hypothyroid adult zebrafish resemble those from adults in the genera Danionella, Devario, and Microdevario that show little to no jaw protrusion. Our findings suggest that evolutionary changes in how the developing skulls of danionin minnows respond to thyroid hormone may have promoted diversification into different feeding niches.

The influence of ontogeny and prey abundance on feeding ecology of age‐0 Lake Whitefish (Coregonus clupeaformis) in southeastern Lake Michigan

AbstractA shift towards oligotrophic conditions in Lake Michigan has led to concern that altered trophic pathways are leading to lower early life survival and recruitment for Lake Whitefish (Coregonus clupeaformis). This study evaluated ontogenetic shifts in age‐0 Lake Whitefish diets and evaluated how feeding ecology and the amount of food eaten varied with prey abundance and composition at a site in southeastern Lake Michigan during 2014–2017. Although prey densities varied among years, cyclopoid copepods were overall the most abundant prey available. In turn, cyclopoids were the predominant prey item in diets each year, particularly for the smallest larval Lake Whitefish. However, there was a tendency for the importance of cyclopoids to decline somewhat in each diet index as fish grew and other prey such as calanoid copepods, Bosminidae, Daphniidae and/or chironomids increased in importance. High zooplankton abundance, especially high cyclopoid abundance, available to the small size groups of Lake Whitefish (&lt;21 mm) in 2014 was associated with high food mass/fish, high number of zooplankton eaten/fish, and low incidence of empty stomachs compared with 2015–2017. As fish grew, the impact of food abundance on prey consumption diminished somewhat, indicating that the relationship between fish feeding ecology and the prey environment can change quickly with fish size during the early life period.

Do marine fish juveniles use intertidal tide pools as feeding grounds?

Several authors have put forward the hypothesis that juveniles of transient marine fish concentrate in intertidal tide pools, not only to benefit from refuge and higher temperatures, but also to use them as feeding grounds. However, there have been no attempts to test this. The feeding ecology of fish was studied in intertidal tide pools to evaluate the importance of these habitats as feeding grounds for non-resident juvenile fish. Fish were collected in 5 beaches in Southeastern Brazil. Juveniles of four species of non-resident fish were identified in the pools: Abudefduf saxatilis (Linnaeus, 1758), Diplodus argenteus (Valenciennes, 1830), Eucinostomus melanopterus (Bleeker, 1863) and Odontesthes argentinensis (Valenciennes, 1835). The most abundant species was A. saxatilis, followed by E. melanopterus and D. argenteus. The diet of those three species was characterized and correlated to the supply of potential food items in the pool where they were collected, in the surrounding intertidal and the nearest subtidal habitat. There was extensive diet overlap among species, largely explained by a generalized predation on copepods. The diet of all species was best correlated to the frequency of resources in tide pools, except for the diet of E. melanopterus which was equally correlated to the intertidal nearby habitat. The consistent similarity between stomach contents and prey availability inside the pool, observed for all species, indicates that intertidal tide pools are likely used as feeding grounds by juvenile stages of these transient fish.

Feeding ecology of fishes associated with artificial reefs in the northwest Gulf of Mexico.

The feeding ecology of two reef fishes associated with artificial reefs in the northwest Gulf of Mexico (GoM) was examined using gut contents and natural stable isotopes. Reefs were divided into three regions (east, central, west) across an east to west gradient of increasing reef complexity and salinity. Gray triggerfish (Balistes capriscus) primarily consumed reef-associated prey (xanthid crabs, bivalves, barnacles) and pelagic gastropods, while red snapper (Lutjanus campechanus) diets were mainly comprised of non-reef prey (stomatopods, fishes, portunid crabs). Natural stable isotopes of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) were measured in consumer muscle tissue as well as potential primary producers. Gray triggerfish occupied a lower trophic position than red snapper, with lower δ13C and δ15N values across all size classes and regions, and generally higher δ34S values. Red snapper had a smaller range of stable isotope values and corrected standard ellipse areas across all size classes and regions, indicating a smaller isotopic niche. Contribution estimates of particulate organic matter (26 to 54%) and benthic microalgae (BMA, 47 to 74%) for both species were similar, with BMA contributions greater across all three size classes (juveniles, sub-adults, adults) of red snapper and all but the juvenile size class for gray triggerfish. Species gut contents and stable isotopes differed by region, with fishes consuming more crabs in the east region and more gastropods in the central and west regions. δ13C and δ15N values generally decreased from east to west, while δ34S increased across this gradient. Results highlight species-specific feeding differences associated with artificial reefs, where gray triggerfish may be more dependent on the reef structure for foraging opportunities. In addition, results offer further information on the integral role of BMA in primary production at nearshore artificial reefs.

Ecosystem type shapes trophic position and omnivory in fishes

AbstractThe identification of patterns in ecological characteristics of organisms is a central challenge in macroecology with a growing research interest. The goal of this study was to establish whether patterns in trophic ecology (trophic position and omnivory) of fishes can be extended to an ecosystem dimension (freshwater vs. marine environments), based on the premise that differences in environmental and ecological conditions of aquatic ecosystems have a large influence on the feeding ecology of fishes. To elucidate any relationship between trophic ecology and ecosystem type, we compiled a database using a global data set for fishes (http://www.fishbase.org). The database included 5,426 species distributed in 53 orders based on three common feeding strategies (herbivory, filter‐feeding and predatory). Trophic position and omnivory increased from freshwater to marine ecosystems in filter‐feeding and predatory species. In herbivore species in contrast, omnivory decreased, whereas no statistically significant trends were found for trophic position, which may reflect a similar diet specialization on primary producers regardless of ecosystem type. These findings suggest that ecosystem type has a marked effect on trophic position and omnivory in fishes, but the impact depends on the type of feeding strategy. Prey availability, inherent feeding traits linked to the phylogenetic relatedness of species, ontogenetic effects, spatial variability (habitat‐related factors) and body size are considered as responsible factors for the observed patterns. Our findings demonstrate consistent patterns in trophic characteristics of organisms linked to ecosystem type and underline the usefulness of fishes as model organisms to test macroecology hypotheses.

Food and feeding habits of critically endangered bagrid catfish Hemibagrus punctatus (Jerdon, 1862) (Teleostei: Bagridae) in the Cauvery River, South India

The aim of the study was to investigate the variation in diversity and abundance of food items in Hemibagrus punctatus in relation to season and also to assess its food preference and feeding behaviour which may reflect the availability of prey items in upstream and downstream areas of Hogenakkal area under the Cauvery river systems. Through its stomach content analysis, the fish has been found to be omnivorous and euryphagous, with only a few qualitative differences in the diet. Feeding rate was found to vary in relation to monsoon caused environmental changes during the course of a year. Among the wide variety of prey consumed, juvenile fishes (39.88%) formed an important dietary component. The next major food group was insects (19.50%) followed by diatoms (11.54%), green algae (8.40%), crustaceans (7.29%), blue green algae (3.98%), plant matter (2.79%), worms (2.71%), copepods (1.33%), cladocerans (1.33%), and mollusks (1.33%). All the food items of this fish (% of food- composition) was found vary in monthly. The present findings would facilitate the examination of complex food and feeding regimes of fishes and would help identify the groups of species that use similar resources within a specific community and could also serve as a reference database for feeding ecology of fishes in highly impacted tropical habitats.

Comparing the fish assemblages and food‐web structures of large floodplain rivers

Abstract The Upper Zambezi, Kavango and Kwando are large floodplain rivers with substantial biodiversity, providing water and ecosystem services to a large tract of southern Africa. These rivers differ in hydrological regime. The Upper Zambezi and Kavango rivers are in flood for 4 months (March, April, May, June) while, in the Kwando River, floods are later and last for 1–2 months in July and August. The Upper Zambezi River has the largest annual flood pulse, followed by the Kavango River, while the Kwando River experiences small and unreliable floods. During years of exceptional flooding of the Upper Zambezi and Kavango rivers, the rivers are interconnected at peak flows and therefore share a common ichthyofauna. This provided a natural experiment to investigate the responses of fish communities comprised of the same species to differing flood regimes by comparing the fish assemblages and food‐web structures between rivers. Fish assemblage structure was characterised by analysing biomass catch per unit effort data collected using gillnets in all water‐level seasons for all three rivers. Whole ecosystem‐stable isotope data collected once from each river were used to examine differences in food‐web structure and fish feeding ecology between rivers. Due to temporal differences in hydrology, the Upper Zambezi and Kavango river food webs were characterised during the low and falling water seasons, while the Kwando River food web was sampled during the rising water season. In the Upper Zambezi and Kavango rivers, fish assemblages varied with hydrological season due to the homogenising influence of the flood pulse, while in the Kwando River fish assemblages did not change seasonally. The Upper Zambezi River food web had a restricted nitrogen range (NR = 0.90), with a reduced food chain length and predators did not occupy elevated trophic positions compared to those in the Kavango and Kwando river food webs (NR = 1.05 and 0.97 respectively). The Kwando and Kavango rivers are less exploited than the heavily fished Upper Zambezi River, where fishing has reduced the abundance of primary and tertiary consumers, potentially resulting in the observed reduction in food chain length. The Upper Zambezi and Kavango river food webs were based on differing basal resources compared to the Kwando River food web. The Upper Zambezi and Kavango river food webs were likely supported by 13C‐enriched resources such as C4 riparian vegetation from the floodplain, while the Kwando River food web was likely based on 13C‐depleted resources such as filamentous algae and aquatic macrophytes. The influence of the varying flood pulses on the fish communities of these three rivers supports the flood pulse concept. There is also evidence that food‐web structures differ between rivers but, due to differing hydrological regimes in the rivers, further study is required to understand causal factors. These ecosystems are increasingly impacted by human population growth and development, as well as climate change, and improved predictions in fish community and food‐web structure in relation to flood pulse changes are important for ecosystem management in future.