This study was carried out with the following objective: determine the Astyanax altiparanae population structure. Four localities in the Paranapanema river basin were chosen (low Tibagi river) with distinct environmental characteristics. Sampling was carried out monthly from January 1997 to February 1998. A total of 1553 individuals were captured with constancy in all the river extensions, with greatest abundance in the Congonhas river (76%). There was variation among the river extensions in the development phase, length class and spatial distribution of the captured specimens, showing that the species has a differentiated population structure although with similar growth. Therefore, the results suggested that the species has a great adaptive capacity to exploit and using differentiated strategies in terms of population structure. This showed that the species has a strong tendency to r strategic behavior. It showed, however, preference for developing all its biological cycle at the Congonhas river first extension. This was probably due to environmental conditions favorable to the maintenance of the specie.
Ecology; fish; Tibagi
