Auto-ecological responses of rainbow trout populations to ecoregional differences in a neotropical andean river

Abstract

We assessed changes in auto-ecological traits of Rainbow Trout (Oncorhynchus mykiss) in a river flowing through two ecoregional belts. Besides the temperature and elevation, these ecoregional belts mainly differed in terms of the presence or absence of riparian forest (high-Andean and páramo regions, respectively). Our results indicated that fish populations in the páramo attained sexual maturity at a smaller size and fed mainly on autochthonous small aquatic invertebrates such as chironomid midges and caddisflies. In the high-Andean reach, Rainbow Trout attained larger sizes and there was a segregation in the use of food resources; adults fed primarily on allochthonous resources and juvenile fish on autochthonous prey items. Overall, our results suggested that limited availability of resources did not constrain the successful establishment of Rainbow Trout in Andean streams but appeared to have a direct effect on some auto-ecological characteristics such as sexual maturity, size and diet. The variability of the evaluated traits seemed to be linked to the presence or absence of resources provided by a well-developed riparian forest, instead of variability in temperature, water quality or flow regime.