Trophic ecology and condition factor of two sympatric species of Hemigrammus from a stream of the Negro River Basin, Brazilian Amazon

This study aimed to evaluate the diet and condition factor of Hemigrammus levis and Hemigrammus coeruleus in a stream in the Tupé Sustainable Development Reserve, in the lower Negro River region, and contribute information on the biology of small species of fish. Ecological aspects, such as food composition, prey use and availability, fractional trophic level, trophic niche amplitude, food overlap and condition factor, were analyzed. The collections took place during the high-water period in December 2019 and January 2020, using sieves and hand nets. The captured specimens were taken to the Ichthyology Laboratory at UFAM for analysis. The results showed that both species mainly consume insects (H. levis: alimentary index AIi%> 90%; H. coeruleus: alimentary index AIi%>50%), with a preference for similar food items. The analysis of food overlap indicated low competition for resources, suggesting a harmonious coexistence between the two species. H. levis presented a specialized diet and feeds on insects, while H. coeruleus has a more generalist diet. The relative condition factor (Kn) close to 1 suggests that both species had an excellent state of well-being. This information is valuable for monitoring ecosystems, since changes in the diet of species can indicate environmental changes or impacts caused by human activities. In addition, the information demonstrates that management practices that preserve the adjacent forest are necessary, as it provides allochthonous food for aquatic fauna and is therefore essential to ensure the survival of the species.