Explore the vast range of titles available.

Information on fish trophic levels is important to assess fishing impacts and to better understand the bioaccumulation of pollutants within aquatic food chains. The local ecological knowledge held by small-scale fishers can fill knowledge gaps in fish trophic ecology. We estimated the trophic levels of 69 tropical and subtropical fish species (33 coastal and 36 freshwater species) using data on fish diets from the literature and obtained from interviews with Brazilian fishers. The fish trophic levels estimated from fishers’ knowledge were positively correlated with the trophic levels estimated using data from biological studies for both coastal and freshwater fish. The fishers’ knowledge also indicated bioaccumulation patterns, as the fish trophic levels estimated from fishers’ knowledge were positively related to the mercury (Hg) content in fish muscle (wet weight, from literature data) in 41 fish species (15 coastal and 26 freshwater). These findings reveal the potential for new applications of fishers’ knowledge to ecotoxicology, which could improve management of aquatic ecosystems and strengthen fishers’ political status.

Variations in levels of parasitism among individuals in a population of hosts underpin the importance of parasites as an evolutionary or ecological force. Factors influencing parasite richness (number of parasite species) and load (abundance and biomass) at the individual host level ultimately form the basis of parasite infection patterns. In fish, diet range (number of prey taxa consumed) and prey selectivity (proportion of a particular prey taxon in the diet) have been shown to influence parasite infection levels. However, fish diet is most often characterized at the species or fish population level, thus ignoring variation among conspecific individuals and its potential effects on infection patterns among individuals. Here, we examined parasite infections and stomach contents of New Zealand freshwater fish at the individual level. We tested for potential links between the richness, abundance and biomass of helminth parasites and the diet range and prey selectivity of individual fish hosts. There was no obvious link between individual fish host diet and helminth infection levels. Our results were consistent across multiple fish host and parasite species and contrast with those of earlier studies in which fish diet and parasite infection were linked, hinting at a true disconnect between host diet and measures of parasite infections in our study systems. This absence of relationship between host diet and infection levels may be due to the relatively low richness of freshwater helminth parasites in New Zealand and high host–parasite specificity.

Bottom trawling is one of the main pressures on benthic ecosystems, directly impacting the targeted species and physically disturbing the seabed and the benthic invertebrate communities, in turn indirectly impacting benthivorous fish and the entire benthic food web structure and functioning. To predict the cascading effect of bottom trawling on benthic and demersal fish communities, it is crucial to understand the trophic interactions between benthic and demersal fish and benthic invertebrates. Here, we assessed the diet of benthic and demersal fish and the structure and functioning of the benthic food web in two areas in the German Baltic Sea, the Fehmarnbelt and the Odra Bank. The Fehmarnbelt benthic invertebrate community is characterized by a high number of species and biomass, contrary to the one on the Odra Bank which is species poor with high individual abundance but low biomass. We used mixing models based on stable isotopes of carbon and nitrogen combined with stomach content analyses to estimate the fish diet at both sites, and we used community-wide trophic indices, derived from stable isotopes to compare the structure and functioning of the fish benthic food webs. We show that fish in the Fehmarnbelt can chose preferential prey items, resulting in higher trophic diversity, contrary to fish on the Odra Bank, which feed on all available prey species, resulting in higher trophic redundancy. We found that the generalist behavior of fish on the Odra Bank is likely the result of scarcity in prey items, the benthic invertebrate community being species poor with high abundance of small individuals. We demonstrate that the differences in structure and functioning of the benthic fish food web between the two sites was mainly driven by differences in the characteristics of the benthic prey communities.

The occurrence of low dissolved oxygen (hypoxia) in coastal waters may alter trophic interactions within the water column. This study identified a threshold at which hypoxia in the northern Gulf of Mexico (NGOMEX) alters composition of fish catch and diet composition (stomach contents) of fishes using fish trawl data from summers 2006–2008. Hypoxia in the NGOMEX impacted fish catch per unit effort (CPUE) and diet below dissolved oxygen thresholds of 1.15 mg L⁻¹ (for fish CPUE) and 1.71 mg L⁻¹ (for diet). CPUE of many fish species was lower at hypoxic sites (≤ 1.15 mg L⁻¹) as compared to normoxic regions (> 1.15 mg L⁻¹), including the key recreational or commercial fish species Atlantic croaker Micropogonias undulatus and red snapper Lutjanus campechanus. Overall, fish diets from hypoxic sites (≤ 1.71 mg L⁻¹) and normoxic sites (> 1.71 mg L⁻¹) differed. Fish caught in normoxic regions consumed a greater mass of benthic prey (ex. gastropods, polychaetes) than fish caught in hypoxic regions. Hypoxia may increase predation risk of small zooplankton, with observations of increased mass of small zooplankton in fish stomachs when bottom hypoxia was present. Changes in contributions of small zooplankton and benthic prey to fish diet in hypoxic areas may alter energy flow in the NGOMEX pelagic food web and should be considered in fishery management.

— The paper presents characteristics of the species composition, spatial distribution, and trophic interactions of ichthyoplankton and zooplankton in the spring–summer period 2017 dependent on intensity of the warming-up of the upper sea layer against the background of transition in a system of the surface currents from the winter-to summer-type of the circulation. In April–May, successful spawning of temperate-water fish species was prolonged due to low values of the sea surface temperature (8–9°С) on the shelf of Crimean Peninsula between Kerch Strait and the cape Sarych. The maximum abundance of Sprattus sprattus eggs was 162.8 egg/m 2 and larvae –116 ind/m 2 . Warm-water species occurred only in the western sector from Herakleian Peninsula to the Cape Tarkhankut, where the water temperature was at its maximum and peaked at 14–15°С. In June–July the delayed summer hydrological season hampered the warming-up of the upper quasi-homogenous layer, which thickness varied from 1–5 to 10–15 m. Notwithstanding the large number of species in the ichthyoplankton, maximum abundance did not exceed 50 egg/m 2 and 14 ind/m 2 for larvae. The proportion of larvae of temperate-water fish species averaged 32% and reached 40% in deep water areas. Juvenile stages of copepods of the cold-water complex were dominant in the larval fish diet both in the spring and summer seasons.

Ecological monitoring contributes to the understanding of complex ecosystem functions. The diets of fish reflect the surrounding environment and habitats and may, therefore, act as useful integrating indicators of environmental status. It is, however, often difficult to visually identify items in gut contents to species level due to digestion of soft‐bodied prey beyond visual recognition, but new tools rendering this possible are now becoming available. We used a molecular approach to determine the species identities of consumed diet items of an introduced generalist feeder, brown trout (Salmo trutta), in 10 Tasmanian lakes and compared the results with those obtained from visual quantification of stomach contents. We obtained 44 unique taxa (OTUs) belonging to five phyla, including seven classes, using the barcode of life approach from cytochrome oxidase I (COI). Compared with visual quantification, DNA analysis showed greater accuracy, yielding a 1.4‐fold higher number of OTUs. Rarefaction curve analysis showed saturation of visually inspected taxa, while the curves from the DNA barcode did not saturate. The OTUs with the highest proportions of haplotypes were the families of terrestrial insects Formicidae, Chrysomelidae, and Torbidae and the freshwater Chironomidae. Haplotype occurrence per lake was negatively correlated with lake depth and transparency. Nearly all haplotypes were only found in one fish gut from a single lake. Our results indicate that DNA barcoding of fish diets is a useful and complementary method for discovering hidden biodiversity. In this paper sequence‐based DNA barcoding was applied to determine the diet of a generalist predator (brown trout, Salmo trutta) based on gut analyses. Subsequently, the results were compared with data derived from visual inspection. Based on our results, we discuss the potential of using prey organisms in fish gut contents as a supplementary monitoring tool to reveal hidden biodiversity.

Line-diffuser hypolimnetic oxygenation was initiated in North Twin Lake, Washington, in 2009 to mitigate reductions in Rainbow Trout ( Oncorhynchus mykiss ) and Brook Trout ( Salvelinus fontinalis ) habitat due to temperature-dissolved oxygen “habitat squeeze”. Previous studies demonstrated that trout populations rapidly expanded into increased hypolimnetic habitat within the first few years of oxygenation and previous short-term diet analyses indicated an effect on fish diet; however, the long-term effects on fish ecology have yet to be established. In this study, stable isotope analysis of fish liver tissue suggests relatively few differences in feeding ecology of principal coldwater fish species in North Twin Lake compared to unoxygenated South Twin Lake. When compared between lakes, Rainbow Trout and Brook Trout diets contained similar proportions of Daphnia , Chironomidae, and Chaoboridae. Littoral and epilimnetic-focused Golden Shiner ( Notemigonus crysoleucas ) diets were also similar between lakes. Observed similarities between Golden Shiner and trout diets suggest the effects of interspecific competition between salmonids and non-salmonids may be limiting trout growth and survival. Fisheries managers should therefore consider both habitat limitations and interspecific competition when managing for coldwater fish species in mesotrophic, dimictic lakes.

Functional traits are growing in popularity in modern ecology, but feeding studies remain primarily rooted in a taxonomic‐based perspective. However, consumers do not have any reason to select their prey using a taxonomic criterion, and prey assemblages are variable in space and time, which makes taxon‐based studies assemblage‐specific. To illustrate the benefits of the trait‐based approach to assessing food choice, we studied the feeding ecology of the endangered freshwater fish Barbus meridionalis. We hypothesized that B. meridionalis is a selective predator which food choice depends on several prey morphological and behavioral traits, and thus, its top‐down pressure may lead to changes in the functional composition of in‐stream macroinvertebrate communities. Feeding selectivity was inferred by comparing taxonomic and functional composition (13 traits) between ingested and free‐living potential prey using the Jacob's electivity index. Our results showed that the fish diet was influenced by 10 of the 13 traits tested. Barbus meridionalis preferred prey with a potential size of 5–10 mm, with a medium–high drift tendency, and that drift during daylight. Potential prey with no body flexibility, conical shape, concealment traits (presence of nets and/or cases, or patterned coloration), and high aggregation tendency had a low predation risk. Similarly, surface swimmers and interstitial taxa were low vulnerable to predation. Feeding selectivity altered the functional composition of the macroinvertebrate communities. Fish absence favored taxa with weak aggregation tendency, weak flexibility, and a relatively large size (10–20 mm of potential size). Besides, predatory invertebrates may increase in fish absence. In conclusion, our study shows that the incorporation of the trait‐based approach in diet studies is a promising avenue to improve our mechanistic understanding of predator–prey interactions and to help predict the ecological outcomes of predator invasions and extinctions. Although functional traits are growing in popularity in modern ecology, feeding studies remain firmly rooted in a taxonomic‐based perspective. Our study shows that morphological and behavioral traits may explain prey vulnerability to predation and, consequently, suggests that the adoption of a trait‐based perspective in feeding ecology studies can improve our mechanistic understanding of prey–consumer relationships.

Beneficial effects of n-3 fatty acids on a variety of physiological functions have been reported, but information related to the effects of oily fish consumed within a varied diet on glucose metabolism and diabetes risk is scarce. The objective of the study was to compare the effects of a diet rich in oily fish to those of a diet rich in red meat on lipid profile, oxidative status, glucose metabolism and insulin sensitivity in young, iron-deficient women. The study was designed attending the CONSORT statement guidelines. It was a randomised crossover dietary intervention study with two 8-week periods. Two diets were designed differing only in their oily fish or red meat content (four portions per week). Twenty-five young iron-deficient women with normal lipid, glucose and insulin levels participated in the assay. Lipid profile (total, LDL- and HDL-cholesterol, TAG), fasting glucose, fasting insulin, and oxidation (lipoperoxides) and inflammation (soluble intercellular adhesion molecule-1 and soluble vascular cell adhesion molecule-1) biomarkers were analysed. Insulin sensitivity was assessed by the Homeostasis Model Assessment (HOMA) and Quantitative Insulin Sensitivity Check Index (QUICKI). Insulin levels significantly decreased and insulin sensitivity significantly increased with the oily fish diet. HDL-cholesterol significantly increased with the oily fish diet. Other parameters did not significantly differ between diets. An increase in oily fish consumption increases insulin sensitivity in young iron-deficient women. This outcome should be considered when giving dietary advice to this population.