Age, growth and mortality of the cichlid fish Oreochromis niloticus (L.) from the River Nile at Beni Suef Governorate, Egypt.

Monthly samples of Oreochromis niloticus from the River Nile at Beni Suef were collected during the period from January 2009 to December 2010. The Von Bertalanffy growth function parameters were: L_∞ = 48.14 cm, K = 0.147 y^-1, and t_0 = 0.2237 year. The total mortality coefficient (Z) was calculated as 0.9654 yr^−𝟏, the natural computed mortality coefficient (M) was 0.4010 yr^−𝟏 with fishing mortality (F) estimated as 0.5643 yr^−𝟏 and exploitation ratio (E) calculated as 0.5819. This high exploitation ratio shows that the stock of Oreochromis niloticus from the River Nile at Beni Suef is overexploited.