Long-term monitoring of potamodromous migratory fish larvae in an undammed river

Abstract

Freshwater fish reproduce annually in environments that provide favourable conditions for spawning and larval survival and growth. Thus, the aims of this study were to use long-term larval density data to evaluate the temporal distribution of the dourado Salminus brasiliensis, its habitat use for larval development and the effects of environmental variables on reproduction. S. brasiliensis larvae were mainly recorded in October and January in the Ivinheima River, and higher densities of larvae, primarily in the preflexion and flexion stages, were captured in the river and backwater biotopes. Water level, dissolved oxygen and temperature were the primary variables affecting the density of larvae, and this species can migrate over 200km to reproduce in the Ivinheima River and its tributaries. Therefore, S. brasiliensis is reproducing annually, indicating favourable local conditions for migration and spawning, and exhibits differential use of biotopes for reproduction, including rivers and backwaters (spawning) and lagoons (refuge and growth). Therefore, considering that the dourado is a key species for conservation, ensuring its reproductive success means maintaining a balanced ecological structure.