Flipped reducetarianism: A vegan fish subordinated to carnivory by suppression of the flooded forest in the Amazon

Abstract

The effects of dams closure and floodplain forest removal on diet and body condition of a frugivorous migratory fish from the Amazon were evaluated herein. Fish were captured with gillnets in two different environmental conditions: before and after the construction of the Santo Antônio reservoir in Madeira River, preceded by clearing of floodplain forest to mitigate the effects of eutrophication into the run-of-river dam. A total of 493 Mylossoma duriventre specimens were accessed and showed a strong shift in diet while body condition did not change after reservoir formation. The vegan diet based on fruits and seed was associated to Mylossoma duriventre prior to damming, and replaced by a carnivorous one, mainly based on insects. Our results suggest that dietary plasticity has guaranteed its body condition, at least in the first two years after damming. Cutting off floodplain forest to avoid eutrophication has immediate and direct impacts upon the supply of fruits and seeds for Mylossoma duriventre. Still, substitution with insectivorous diet over a frugivorous one, as observed for Mylossoma duriventre, may conceal an underlying problem of decreasing the local ichthyochory and floodplain forest maintenance or restoration of várzea areas over the time.