Dieta e crescimento de Oreochromis niloticus capturada na Albufeira de Massingir

Abstract

The present work was carried out from July to September 2007, in Massingir Reservoir, at the Cubo fishing centre, with the aim of studying the diet and growth of the Nile Tilapia (Oreochromis niloticus). A total of 150 fishes were sampled, of which 126 were females and the remaining 24 were males. Of the sampled fishes, analysis of stomach contents was carried out on 95 fishes that had contents while the remaining fishes had empty stomachs. The analysis of stomach contents was done by the method of percentage frequency of occurrence of different food items present in the stomach. This method consisted of observing the stomach contents under microscope and counting the first 100 food items present in each stomach. Also, the total length and weight of the fish was measured to determine the total length - total weight ratio. Maturity stages were determined based on the physical appearance of the gonads for comparison of diet at different stages of maturity using the Morisita index. The weight of gonads was determined to analyse its relationship with total length and total weight. Fourteen genera (02 zooplankton and 12 phytoplankton) belonging to 12 families and 6 divisions were counted. The most frequent genera were Ceratium (100%) of occurrence, Fragilaria (87.4%), Meiosira (64.2%) and Pediastrum (47.5%). The most representative divisions were Chlorophyta and Chrysophyta. There is a strong linear correlation between total length and total weight in both sexes. Maturity stage I and II fishes predominated in the August sample while maturity stage III fishes predominated in September. There is overlapping of diet in different maturation stages (C=1). (TRADUÇAO NOSSA)