Aspectos estruturais da assembléia de peixes de uma lagoa marginal do submédio São Francisco, após sua desconexão e deplecionamento

Abstract

Marginal lakes are considered as important grounds for nursery, protection and shelter for fish. These and their connecting channels to the river constitute growout and adult recovery areas, being characterized by various aquatic and transitional habitats between aquatic and terrestrial environments, which occupy lateral river depressions and present permanent or intermittent connection to them. The medium São Francisco river has been the object of hydroelectrical enterprises viability studies, which may significantly modify the fish fauna composition in the region as well as its reproductive dynamics. Owing to the role of such lakes for fish species inhabiting the lotic stretch above the Itaparica reservoir and its relation to migratory species populations, the ichthyofauna characterization assumes uttermost importance, before such enterprises are installed in the region. Samplings with various fishing devices were undertaken between March 2007 and February 2008, in the Curralinho lake, a marginal pond located in the submedium São Francisco river, aiming at evaluating the fish fauna composition after its isolation from the river channel and water depletion. A total of 4,638 specimens was collected, with a biomass of 129,782.84 g, distributed in 16 families and 45 species from the Orders Characiformes, Cyprinodontiformes, Siluriformes, Perciformes, Gymnotiformes and Clupeiformes. Diversity and biomass presented strong correlation with water dissolved oxygen concentration, transparency and electrical conductivity, and equitability with water pH. Characiformes were most abundant and 87.3% of the specimens were small (<100 mm) or medium-sized (<200 mm). Among the 47 species collected, 26.7% were constant, 35.6% accessory and 37.8% accidental. Characidae encompasses most of the species and individuals, followed by Acestrorhynchidae. Moenkausia costae, Triporhteus guentheri, Pygocentrus piraya and Prochilodus argenteus were present in all samples. Invertivores and piscivores dominated quantitatively and their biomass indicate a predominance of predators, with detritivores presenting the second greatest biomass. Residentspecies prevailed, with few individuals of migratory fish belonging to Anostomidae,Prochilodontidae and Salminus franciscanus. Fish richness, diversity and equitability were relatively high throughout the period of study. It may be concluded that the Curralinho lake is an important shelter, feeding and resting ground for the ichthyofauna, mainly for forage fish that serve as the basis of the trophic chain and fisheries´ sustainability. Therefore, there is an urgent need of environmental policy and management practices development that would preserve habitat integrity and functionability of their role in the conservation of ichthyodiversity of this stretch of the São Francisco basin.