Growth, Mortality and Exploitation of Nile tilapia, Oreochromis niloticus (L.) in Lake Chivero, Zimbabwe and Implications on the Management of the Artisanal Fishery

Age and growth of Nile tilapia, Oreochromis niloticus (L.) were determined using sample from Lake Chivero (Zimbabwe) caught from 2009 to 2011. The length-weight relationship for all individuals was W = 0.015 TL0.304. The sex ratio of female to male was 1:1.27. Fish age derived from both length frequencies and scales showed no significant difference (p > 0.05, Paired T-test). The length frequency age data were used to estimate the growth parameters of the von Bertalanffy equation. The mean values from 2009 to 2011 were: L∞ 39.41, K = 0.41, (ø) = 2.798, Lm50 = 23.33 cm, Lc50 = 22.60 cm, Z = 1.84 year-1, M= 0.81 year-1, F = 1.04 year-1 and E = 0.58 year-1. Growth, mortality and exploitation parameters L∞, K, (ø) and Z were compared from year to year and results showed the fishery is over-exploited. Fish below age/length at first maturity form the bulk of the fish harvested by the fishery. Increasing length at first capture could increase yield per recruit and also protect spawning stock. Other implications on the management of the fishery are discussed.Keywords: Exploitation, Fisheries, Growth, Management, Mortality, Nile tilapi