A comunidade ictiológica na albufeira de cahora bassa e suas interacções tróficas

Abstract

The present study was carried out in the Cahora Bassa Reservoir and aimed to describe and qualitatively evaluate the specific diversity of fish fauna, characterize their eating habits and finally propose a diagram of trophic interactions of fish fauna. In the three sub-basins studied, namely Garganta, Chicoa and Mague, 19 fish species belonging to 9 families were recorded. The most representative families were Cichlidae, Characidae and Mormyridae. The most abundant species were Hydrocynus vittatus, Oreochromis niloticus, Tilapiarendalli, Limnothrissa miodon, Mormyrus longirostris and Synodontis zambezensis. The total number of species present in the Cahora Bassa Reservoir is smaller than that reported before the construction of the dam. The analysis of the stomach contents of 16 species was carried out, using the method of percentage of frequency of occurrence of different items in the stomachs. The results of the present study show that omnivory is the most successful food strategy for colonizing this new environment created by the construction of a dam. About 94% of the studied species are omnivorous and only one piscivorous species Hydrocynus vittatus was observed. Registered food items were. phytoplankton, zooplankton, debris, oligochaeta, insects, molluscs, seeds, shrimp and fish. The diet overlap index of all studied species was determined and it was found that in 35 cases the diet overlap was considered biologically significant, in no case was there total diet overlap and in 5 cases there was no diet overlap. The highest percentage of overlap (97.6%) was found between Oreochromis niloticus and Oreochromis mortimerii. The trophic diagram proposed for the fish fauna of the Cahora Bassa Reservoir corresponds to a complex and reticulated network of trophic interactions, with a single piscivorous species Hydrocynus vittatus, at the top. (TRADUÇÃO NOSSA)