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vol-35POPULATION CHARACTERISTICS OF TILAPIA ZILLII
(GERVAIS, 1848) IN LAKE TIMSAH, SUEZ CANAL, EGYPT.
AZZA A. EL-GANAINY AND MANAL M. M. SABRA
National Institute of Oceanography and Fisheries, Suez Branch,
P.O. Box 182, Suez, Egypt.
Tel: +20643366172
Fax: +20623360016
E-mail address: [email protected]
Keywords: Tilapia zillii, Lake Timsah, age, growth, mortality, yield per recruit.
ABSTRACT
The population parameters of Tilapia zillii from Lake Timsah were studied. 1638
specimens with total length ranging from 7.5 to 21.3 cm were collected monthly from the
small scale fishery of Lake Timsah during the period from October 2002 through February
2004. The length weight relationship was calculated to be W = 0.0217 L 2.9555. The oldest
age stimated from otolith reading was 4 year. Age group one was the most predominant in
the catch represented by about 73.0 % of the individuals. The parameters of von Bertalanffy
growth equation were L∞= 21.87 cm, K= 0.46 year-1 and to= -0.499 year. The values of
natural mortality (M), total mortality (Z) and fishing mortality rates were 0.712, 2.260 and
1.548 Y-1 respectively. The fishing mortality rate was substantially greater than both the
target (Fopt = 0.356/yr) and limit (Flimit = 0.474/yr) biological reference points. Analysis of
the yield per recruit postulated that the fishing pressure exerted in Lake Timsah has
exceeded the critical level, and that juvenile individuals are the target of the fishery. This
implies that the stock dynamics of this species would be seriously affected. Reductions in
the fishing effort and mesh size regulations are required for the protection of the resource.
