Fish feeding selectivity from Atlantic forest coastal streams, southeastern Brazil

Background/Question/Methods

The Atlantic forest coastal streams are inserted in a Brazilian biome highly threatened by deforestation, and its ichthyofauna is poorly known. Considering that the understanding of fish species distribution depends on the knowledge of fish feeding habits and food resource availability, this study aimed to investigate the feeding selectivity of fish fauna of seven pristine Atlantic forest coastal streams. Four samples were taken to cover one-year collection. Fishes were caught with an electrofisher gear. Preys availability was obtained by using two plastic trays (34 x 23 cm), placed on each stream margin, and a Surber sampler (900 cm², 250 µm mesh) in the same stretches used for electrofishing. Macroinvertebrates sampled with electrofishing were also accounted. Considering that insects are an important feeding resource for several stream fish species, an Index of Relative Importance was calculated for insectivorous species to determine the predominantly insect order for each fish species diets. The evaluation of selectivity (or preference) by insect orders was made by the Electivity index, which considers both consumed food items as its availability in the environment.

Results/Conclusions

A total of 21,451 invertebrates were captured. Crustaceans and insects predominated. Among insects, dipterans were numerically abundant. The diet analysis of 18 fish species (1,659 guts evaluated) resulted in 12 species classified as insectivores, four as detritivores, and two as omnivores. Insects were the most consumed resource. Considering the resources availability, allochthonous and autochthonous items were found in similar proportions in the environment; however, this representativeness varied according to the fish feeding habits. Crenuchidae species were highly selective for mayflies (Ephemeroptera), considering the low availability and high consumption of this food resource in the streams. In contrast, three Characidae and one Heptapteridae species consumed mainly insects with greater availability in the environment, evidencing their opportunism. The striking presence of insectivores fish reinforces the importance of insects to sustain the food chain in the studied system, but also reflects the diversity and abundance of the order Diptera. Our results also underscore the importance of Brazilian Atlantic forest conservation and confirm the role of riparian vegetation as food provider for stream fishes, as it contributes to the input of coarse particulate organic matter (the basis for aquatic food chain, as well as terrestrial insects (food for several fish).