Diet composition of the vulnerable fish species Megalops atlanticus (Elopiformes: Megalopidae) in a heavily urbanized estuary in Brazil: DNA-based identification of preys

Abstract

The tarpon (Megalops atlanticus) is a species of ecological and economic importance that uses estuaries as nursery grounds during its early life stages. Currently classified as Vulnerable (VU) by the IUCN due to anthropogenic pressures, understanding its trophic ecology is crucial to monitoring environmental changes and fish-habitat interactions. This study examined the diet of juvenile M. atlanticus in a highly urbanized estuary, using morphological and molecular (16S rDNA) analyses, comparing diets across different size classes and assessing the consumption of non-native species. The stomach contents of 123 individuals (3.9–64.0 cm standard length) were analyzed. Results show that M. atlanticus is a generalist and opportunistic, consuming invertebrates as well as native and non-native fish species, including Oreochromis niloticus. The presence of Tubifex spp. and evidence of cannibalism indicate dietary plasticity in response to altered environments. The DNA-based approach allowed for more accurate prey identification, reinforcing that the diet of juveniles is shaped by the presence of non-native species, which are common in habitats modified by human activities. These findings highlight the impact of anthropogenic actions on trophic dynamics in estuaries and emphasize the essential role of these habitats as nursery grounds for tarpon.

Keywords:
Coastal ecosystem; DNA; Estuarine fish; Feeding habits; Urban ecosystem