AIM: The genus Astyanax is one of the richest in number of species and has one of the widest geographical distributions in Argentina, being possible to find in nine ichthyogeographic ecoregions. The aim of the present work was to analyze the population structure of Astyanax fasciatus in the Garupá Stream, Province of Misiones, Argentina, considering its distribution by size, standard length-total weight relationship and aspects of its reproductive and feeding biology; METHODS: A total of eight experimental fishing campaigns were carried out between September 2002 and May 2004, in agreement with the seasons of the year, using a set of gillnets; RESULTS: We captured a total of 386 individuals, 70% of which in the Middle Basin in autumn and winter. The following gonad stages were identified in both males and females: resting, maturing, mature and spawning. The highest gonadal activity corresponded to the autumn-winter period. The Middle Basin showed the highest capture of individuals in reproductive activity, thus reflecting the seasonality of spawning. The average fecundity was of 4000 oocytes, being 1100 µm the largest oocyte diameter. The mean standard length of the total catch was 99.3 mm and females reached larger sizes than males (P < 0.05). The standard length varied according to the seasons of the year. Both sexes presented an isometric growth (b = 3). Females presented the highest values of K in spring and summer, whereas males did so in spring. The K-GSI relationship reflected that the highest K values corresponded to the lowest GSI ones. We found that A. fasciatus feeds on a wide variety of foods of both plant and animal origin. The food items of plant origin presented the highest index of occurrence; CONCLUSIONS: The long spawning seasons and the recruitment along all four seasons of the year allow characterizing A. fasciatus as a foraging species that is very well adapted to the environment studied in this work.
Astyanax fasciatus; population; reproduction; feeding; Garupa Stream
