The present study investigated energy allocation patterns in three fish species from the family Hemiodontidae (Argonectes robertsi, Hemiodus microlepis, and Hemiodus unimaculatus), before and after the construction of Lajeado Dam, Tocantins River, Amazon basin. Changes in the use of energy (between somatic and reproductive processes) were indirectly evaluated by means of temporal variations in fish body condition, feeding activity, visceral fat storage, and reproductive effort. Fish were collected from October 1999 to September 2004, in periods that preceded and followed the construction of the dam. We recorded significant changes in all ecological traits for the three analyzed species (for males and females). In general, there was an intense reduction in reproductive activity after river damming, whereas visceral fat and body condition increased consistently. In contrast, there was no clear trend in feeding activity (i.e., stomach weight), with little changes in species diet during the analyzed period. These results indicate that the impoundment changed the energy allocation process between somatic and reproductive activities, since fish started to allocate energy mainly to somatic processes. These changes may have a negative effect on the persistence of populations in Lajeado Reservoir, because improvements in somatic condition will not necessarily translate into increased fitness.
Body condition; Colonization; Fitness; Reproduction; River regulation
