Segregação longitudinal na atividade reprodutiva de peixes Neotropicais como indicador de caráter de migração.

Abstract

Freshwater environments are high heterogenous habitats, justifying the development of different reproductive strategies in fish species inhabiting such habitats. In a spatial perspective, these species can be grouped into migratory and sedentary. Although such classifications seem clear, many uncertainties concerning such species reproductive traits remains. This study proposes to study fish reproductive movement, based on the spatial extent of the occurrence of fish with high reproductive activity along the basin, adopting as model a 400 km stretch of the Cuiabá River. The proposed hypothesis was that migratory species, besides presenting large home range, would present striking spatial segregation among the distinct gonadal development stages. Samplings were performed in the Cuiabá River basin, embracing several environments (river channel, floodplain, and lagoons) between 2000 and 2004, considering only data of the reproductive period (between October and February). The values of the Reproductive Active Index (RAI) were estimated for each species, sampling site, month, and year. A principal coordinates analysis (PCoA) was performed with the values of RAI in order to detect a possible pattern in species reproduction distribution in the basin and to verify if the migratory trait can be indicated by its spatial distribution. The first and second axes of the ordination were applied into Pearson?s correlations with the original RAI values to detect which were the species which contributed the most to the ordination results. Species distribution was estimated through species presence and absence and reproduction sites by the maximum RAI values, consequently, obtaining a filter to identify the migratory species. Migratory species were those that presented positive correlation with the axis 1 of the PCoA, wide distribution in the basin, and reproduction exclusively in the upstream areas. Among the 85 species included in the analysis, 18 were classified as migratory, of which four were never described as so before: Auchenipterus osteomystax, Cynopotamus kincaidi, Iheringichthys labrosus and Pimelodus argenteus. Additionally, the other species how Rhaphiodon vulpinus and Pinirampus pirinampu, previously described as migratory were classified as sedentary. The proposed filter has proved to be effective in the classification of migratory and sedentary species, and aid in the filling of some existing gaps on the reproduction and development of fish species. This is of fundamental importance in the planning of new projects, in decision making, and in the development of management and conservation measures for the fish assemblage.