Fish assemblage structure in a first order stream, southeastern Brazil: longitudinal distribution, seasonality, and microhabitat diversity

Abstract

This study was carried out on a first order stream in the Morro do Diabo State Park, southeastern Brazil. Three equidistant stream stretches - upper, middle, and lower - were chosen for underwater observations and fish collections that were performed in the dry (June and September 2000) and wet seasons (December 2000 and March 2001). Of the 18 fish species documented, 11 were considered resident year round. Phalloceros caudimaculatus, Hypostomus nigromaculatus, Hisonotus francirochai, Trichomycterus diabolus, and Hypostomus ancistroides represented 90% of the collected specimens. The highest richness and abundance occurred during the wet season. In general, the longitudinal addition of species follows the addition of microhabitats. Sexually mature individuals were present throughout the year for the majority of the species, which suggests broad reproductive activity. However, given that most juveniles specimens were collected during the wet season, it is hypothesized that reproduction and survival rates must be higher during this season due to higher availability of critical resources, most probably food and shelter.