This study describes the reproductive biology of a population of Astyanax henseli Melo & Buckup, 2006 from the upper Rio dos Sinos, Caraá, Rio Grande do Sul, Brazil. A total of 336 specimens was analyzed, comprising 169 males, 154 females and 13 individuals of undetermined sex. The reproductive season lasted approximately five months, from August to December, gonadossomatic index (GSI) peaked of in October, corresponding to the end of winter and the spring in the southern hemisphere. No correlation was found between the GSI and abiotic factors (temperature, rainfall and photoperiod). However, these factors may trigger gonad maturation. Also, no correlation was observed between biotic variables, such as stomach repletion index (RI) and hepatosomatic index (HSI), and GSI. Despite that, high RI values during the reproductive period may indicate that A. henseli maintains its feeding activity throughout the reproductive months, while low HSI values during the peak of GSI suggest a higher energy expenditure of the liver during this period. The sex ratio in the population was 1:1 for the total number of individuals sampled, among different classes of length, and among the different months of the year. The size at first gonadal maturation was 69 mm for males and 60 mm for females. The absolute fecundity mean was 3,038 oocytes and the relative fecundity mean was 0.13 oocytes mg-1. The oocyte development indicated that A. henseli is a total spawner.
Reproductive period; small size characid; gonadosomatic index; fecundity; first gonadal maturation
