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The objective of the present study was to determine the diet composition and feeding habits of the crocodile shark, Pseudocarcharias kamoharai, in Ecuadorian waters, Southeast Pacific Ocean, at a general level, as well as by sex, year, and sexual maturity stage. A total of 401 individuals with their respective stomachs were sampled in the Santa Rosa fishery port, Ecuador; 200 were females and 201 males, with a total length (TL) between 50 to 117 cm and 72.5 to 100 cm, respectively. The number of stomach contents analyzed in this study was sufficient to describe the diet of P. kamoharai, as the asymptote was reached at 100 digestive tracts. A total of 24 prey species were identified, out of which 16 were cephalopods and eight bony fishes. The main identified prey species were the cockeyed squid, Histioteuthis heteropsis, the sharpear enope squid, Ancistrocheirus lesueurii, the purpleback flying squid, Sthenoteuthis oualaniensis, the Jumbo flying squid, Dosidicus gigas, and the neon flying squid, Ommastrephes bartramii. Pseudocarcharias kamoharai was considered a specialist predator that preferred five prey species (Bi = 0.09), and differences were observed by sex, years, and maturity stages. The trophic overlap was high in both females and males (Cλ = 0.98) between the years 2012–2013 and 2017–2018 (Cλ = 0.91), as well as between immature and mature individuals (Cλ = 0.95). The trophic level was Tlk = 4.37, which indicates that this species is a quaternary consumer or a tertiary carnivore. [ABSTRACT FROM AUTHOR]

Our study sought to analyze patterns and overlap in prey items consumed by elasmobranch species in southern Brazil through a complex network analysis. We hypothesized that species with the same habitat use would show greater trophic niche overlap and lower diet specialization than species with different habitat use. We conducted a literature survey of the species recorded in southern Brazil and analyzed publications with quantitative data on the diet of each species. We found records of 103 species in the region, of which 58 had their diets analyzed and had quantitative data to contribute to this analysis. The results suggest nested diet patterns in this community. Nestedness may arise for different reasons, and suggests that species might be balancing their high feeding niche overlap through compensatory mechanisms. There are no prior records of such a pattern in elasmobranch communities, which brings to light important information about their feeding niche. Data on prey consumption and temporal and spatial patterns of elasmobranch feeding may yield further insight into how these species are interacting in the environment and assist the investigation of the processes that shaped the current community's trophic structure. [ABSTRACT FROM AUTHOR]

Most of the world’s fish fauna is suffering from different types of human impacts and new conservation tools are required. The fish diet analysis is a tool that has been used to evaluate degradation processes of aquatic environments, however, few long-term studies are performed by several reasons (e.g., lack of funding, opportunity). Our aim was to test whether the fish gut content from biological collections can be used for comparisons with current data and, consequently, be used as a tool for long-term environmental impact studies. We compared the gut content of fish preserved for fifteen years in a biological collection with recently sampled fish, considering the factors size of the specimen, preservation time and preservation form. We did not find differences in the gut content percentage of preservation between fish size classes and preservation time. However, we found differences between preservation form, in which the fish fixed in formalin kept the digestive content preserved while the fish preserved directly in alcohol did not. Thus, we encourage the use of fish gut content from biological collections fixed in formalin for long-term ecological studies. Our findings may help elucidate some long-term effects of human impacts on fish fauna. [ABSTRACT FROM AUTHOR]

The intensity of competitive interactions between fishes is partly determined by prey use and ontogenetic niche shifts. In a wetland where distinct habitat shifts are missing we compared prey use of three generalist benthivorous sunfishes to look for evidence of ontogenetic, interspecific, and 'seasonal' variation in prey composition. Diet analysis revealed evidence of diet ontogeny in warmouth ( Lepomis gulosus, 30-152 mm standard length, SL), but not in bluespotted sunfish ( Enneacanthus gloriosus, 30-47 mm SL) or dollar sunfish ( Lepomis marginatus, 30-60 mm SL). Bluespotted and dollar sunfishes consumed small dipteran and amphipod prey and had similar diets in both seasons suggesting a potential for strong interspecific competition. In the dry season, warmouth shifted from using smaller insect prey to larger decapod and fish prey with increasing size. This shift to prey types that were little used by the other species reduced dietary niche overlap with the other sunfishes. After drought and re-flooding (in the wet season), decapods and small fish were less abundant in the wetland and the warmouth ontogenetic shift was less distinct. When matched for gape width, prey composition differed between warmouth and both dollar and bluespotted sunfishes in the wet season, suggesting differences in sunfish foraging modes, but prey use differences were less clear in the dry season when prey were abundant. Both warmouth ontogenetic diet shifts and seasonal variation in prey use (probably mediated by prey abundance) had strong influences on diet overlap and therefore the potential for intra- and interspecific competition between sunfishes in this wetland ecosystem. [ABSTRACT FROM AUTHOR]