Caracterização da ictiofauna do alto rio Paraguaçu, com ênfase nos rios Santo Antônio e São José (Chapada Diamantina, Bahia)

Abstract

The São José and Santo Antônio Rivers are representative affluents of the Paraguaçu River, although they demonstrated different physiographic qualities, and differ in their degrees of anthropogenic disturbance. ln this chapter, the diet and reproductive features of five abundant fish species, common to both affluents, will be described, as well as the possible effects of the degraded environment of the São José River on the biological parameters of the populations. Feeding was analyzed through the Frequency of Occurrence, and by the Volumetric method, combined in an Alimentary lndex, and the niche width was calculated. ln documenting reproduction, the sex and the state of maturity of the fish were noted, as well as the gonadosomatic relation, sexual ratios, condition factor, and size at first maturation. The results indicate a lesser contribution of allochthonous items in the São José River. This may be due to the effects of deforestation along its margins, which would influence those species that are more dependent upon those resources. ln the Santo Antônio River, the changes in the dietary habits of piscivorous was possibly caused by the diminished availability of their traditional prey, due to the presence of introduced piscivorous. There was a tendency towards a reduction in the average size of the fish, especially of piscivorous species, in the São José River. No differences in the male/female rations were observed. The existence of differences between the two rivers in the size of the smallest sexually mature individuais, principally for females, agrees with the previously recognized flexibility of this parameter in response to distinct environmental conditions. Among the parameters analyzed, the lesser proportion of allochthonous items in the diet of fish from the São José River was marked, and can be considered an indirect result of past mining activity in the area.