Reprodução do pirá-brasília, Simpsonichthys boitonei Carvalho (Cyprinodontiformes, Rivulidae), e caracterização de seu habitat na Reserva Ecológica do Instituto Brasileiro de Geografia e Estatística, Brasília, Distrito Federal, Brasil

Abstract

This study aims to analyze the reproduction and the physical and chemical characteristics of the habitat of Simpsonichthys boitonei Carvalho, 1959, a rare and endemic species of Distrito Federal. The fish were collected with sieve in a temporary pool located in the Reserva Ecologica do Instituto Brasileiro de Geografia e Estatistica (RECOR), rio Taquara basin, Distrito Federal. The specimens were measured (total length in mm), weighted (total weight, feminine gonad weight and body weight in grams), for calculation of condition factor (K), gonad-somatic index (IGS) and gonad index (IG). Physical and chemical analyses of environment were also made. The temporary pool was filled with water for eight months (December to August), with total transparency, depth not surpassing 25 cm, conductivity smaller than 15 µS/cm and pH among 4,70 to 5,11. The dissolved oxygen varied among 2,60 to 4,15 ppm, and the temperature of the water among 20 to 25,5 oC. The analysis of reproduction evidenced that the fish has fractional spawning, whose adult females stay with high condition factor during great part of life, but decreasing with their age. The eggs were deposited in the substratum, and the incubation period varied among 55 to 100 days. In laboratory these eggs were maintained in water, where 15,4% complete the embryonic development. The proportion of females was significantly larger than males. For the characteristics above, we can infer that at least two generations of pira-brasilia can be found in the same flood period.