Post-harvest losses and insect infestation of fish in Tanzania

A study of the insect pests and fungi causing post-harvest losses in four important cured inland fish species in Tanzania was conducted. Attempts to evaluate the extent of losses and to establish the lowest possible salt concentrations which can be used to minimize the losses in fish, caused by insect infestation were made. The fish species dealt with included Lates niloticus L. {Centropornidae, Rastrineobala. argentea {Cyprinidae} both from Lake Victoria, stolothrissa tanganicae (Clupeidae} from Lake Tanganyika and Tilapia species from different parts of Tanzania. Data collection inwolved field work {survey of Dar-es-Salaam markets} and laboratory experiments, The market survey revealed that the common insect pests are beetles, Dermestes maculatus {Degeer} and Necrobia rufipes {Degeer}. Larvae of these beetles were by far more numerous than the adults. D. maculatus were common in Tilapia species and L. niloticus, whereas N. refipes were dominant pests of R. argentea and S.tanganicae. D. maculates and N. rufipes were reared in the laboratory and fed with L. niloticus and S. tanganicae respectively. Fish samples used in these experiments were treated with salt (NaCl) concetrations of 5, 10, 20, and 40% for 10 and 30 minutes prior to drying. L. piloticus treated with 40% salt concentration for 30 minutes showed a significant decrease in loss in Weight. However, treating with 20% salt concentration for more than 30 minutes is recommended for use on costs and palatability considerations. Treating S. tanganicae with 20% salt concentration for 30 minutes was found to be more effective against N. rufipes. Fungi isolated from dried L. niloticus belonged to three genera, Rhizopus, Aspergillus and penicillium. Rhizopus was the most prevalent mould while Penicillium was rare. Finally, recommendations on areas for improved fish preservation have been given. These include the use of fungal inhibitors such as Potassium Sorbate, Sorbic acid and Propionic acid in the treatment of fish prior to drying. Also the importance of hygienic handling of fish during processing particularly sundrying needs to be emphasized.