Trophic ecology of the vulnerable tetra Mimagoniates lateralis (Nichols, 1913) in a blackwater stream of the Atlantic Forest

Abstract: Aim Here we investigated the diet of Mimagoniates lateralis (Nichols, 1913) in a blackwater restinga stream of the Atlantic Forest, aiming to identify the main food sources consumed and to verify if ontogenetic variations occur. Methods Specimens were sampled in January 2024 in the Panema stream, Itanhaém – SP. The diet of 124 individuals was determined through stomach content analysis, and the Feeding Preference Degree (FPD) was used to measure the importance of the consumed items. Results The diet comprised 21 items, among which detritus, plant fragments, and adult Hymenoptera were predominant. Only detritus was classified as a secondary item in terms of feeding preference, while all other items were considered occasional. Larger fish were more likely to consume adult Coleoptera and Hymenoptera, while smaller individuals were more likely to consume items such as Trombidiformes and detritus. Conclusions The results suggest an ontogenetic dietary shift, favoring specific prey and reducing dependence on other food items. The high presence of allochthonous items in the diet of M. lateralis highlights the crucial role of riparian vegetation as an essential source of food resources. The preservation of riparian forests supports the balance of these ecosystems and is vital for the survival of M. lateralis, a species vulnerable to extinction, reinforcing the urgency of effective measures of conservation.