The role of the freshwater shrimp Caridina nilotica (Roux) in the diet of the major commercial fish species in Lake Victoria, Tanzania

Abstract

The major commercial fish species of Lake Victoria at the present time are Lates niloticus, Oreochromis niloticus and Rastrineobola argentea. The contribution of Caridina nilotica in their diet was studied in the Tanzanian waters of Lake Victoria between March, 1999 and January, 2002. Stomach samples were collected during routine bottom trawl surveys in Tanzania. The results show that haplochromines dominate the diet of Nile perch, followed by C. nilotica, R. argentea, juvenile Nile perch, fish remains and other prey. Caridina nilotica predominance in diets decreased as size of the Nile perch increased, as this species switched to haplochromines. Larger perch also feed on their own juveniles. The importance of C. nilotica in the diet of L. niloticus was relatively greater in deeper water than that in shallower stations. The diet of O. niloticus was predominantly algae followed by C. nilotica, dagaa, Chaoborus, Odonata and others. O. niloticus has shifted its diet from strictly herbivory to a more omnivorous diet, feeding opportunistically on the most available food material. The overall diet of R. argentea was predominantly copepods, followed by Chaoborus, Cladocera, C. nilotica, Chironomids and insects. In the present food web, C. nilotica is an important food source for the fish stocks of Lake Victoria. The sustainability of the fisheries of Lake Victoria depends among other things on the abundance and availability of C. nilotica.