Evaluation of Oreochromis niloticus and Tilapia zillii fisheries at Aswan region,River Nile, Egypt

Abstract

Cichlid fish species dominating River Nile at Aswan region (namely Oreochromis niloticus and Tilapia zillii) were collected from the widespread used trammel nets. Analysis of the length-frequency using (FiSAT) computer program revealed that, the estimated the Von Bertalanffy's growth parameters were L∞ = 25.73 cm (asymptotic length); k = 0.73 year -1 for O. niloticus and L∞ = 19.43 cm ; k = 1.4 year -1 for Tilapia zillii . The instantaneous total mortality rate of O. niloticus was 3.64 and 5.60 year -1 for T. zillii. The estimated natural mortality rate was 1.44 for O. niloticus and 2.38 year -1for the second species. The respective fishing mortality rates were 2.2 and 3.22 year -1, while their estimated exploitation rates were 0.60 and 0.57 year-1. The results indicated that, O. niloticus and T. zillii fisheries are overexploited. Therefore, it is recommended to decrease the fishing effort in the area of study and increase the mesh size of the inner layer of trammel nets to at least 3 cm mesh bar to secure profitable fisheries and optimum catch for the future.