Growth, mortality, recruitment and fishery regulation of the Nile Tilapia Oreochromis niloticus (Teleostei: Cichlidae) from Manzala Lake, Egypt

Population parameters of the Nile tilapia, Oreochromis niloticus were studied based on 1500 specimens (8-31cm TL) collected monthly from the Lake Manzala for one year. Age was determined based on scales’ readings and found to be five years. The lengthweight relationship can be expressed as W=0.0143*L3.08. The von Bertalanffy growth equations were Lt=34.51 [1-e-0.38(t+ 0.39)] for growth in length and Wt=776.12 (1-e-0.38(t+0.39)]3.08 for growth in weight. The estimated total, natural and fishing mortality rates were 2.02, 0.82 and 1.20 y-1, respectively. The exploitation rate (E) was 0.59 and size at first capture (Lc) was estimated as 14.4cm TL. The relative yield per recruit reached maximum at an exploitation rate (Emax) of 0.6. Oreochromis niloticus stock may be unsustainable due to intensive fishing pressure to meet demand of growing populations, unless proper action is taken to manage the stocks.