Some fishery aspects of Nile tilapia, Oreochromis niloticus at Rosetta Branch of the Nile River, Egypt

Cichlid fish species dominating in Rosetta Branch of the River Nile were studied. They were collected from the commercial catches of widespread used trammel nets during 2008-2009. Analysis of the species composition revealed that Oreochromis niloticus dominated the tilapia catch followed by Oreochromis aureus and Tilapia zillii. The lengthfrequency of the dominated O. niloticus varied between 11 and 27 cm total length and its length weight relationship was W = 0.023966 L^2.92209. The selection range as deduced from the probability of capture varied according to the mesh size used of the inner layer of the net The selection factor corresponding to the compared two different mesh sized nets, that widely used, was also estimated. The results indicated that the mean selection length should be increased to reach at least 15cm by increasing the mesh size of the inner layer of trammel nets to 60 mm stretched mesh or 30 mm mesh bar. This will lead to increasing the average weight of O. niloticus to 65 gm. These basic data may be helpful in understanding the mesh selectivity and fishery management of the Nile tilapia.