ASSESSMENT OF FAMILY CICHLIDAE INHABITING LAKE MANZALA, EGYPT

Abstract

he age and growth of cichlid fishes inhabiting Lake Manzala were studied during the peried from August 2000 to September 2001, based on the length-frequency bF samples collected by the surrounding nets. Analysis of the data using (FiSAT) computer program returned the estimate of the von Bertalanffy's growth curve parameters as: L∞ = 28.88 cm (total length); k = 0.53 year -1 for Oreochromis niloticus; L∞ = 21.53 cm; k = 0.59 yr -1 for aureus; L∞ = 23.63 cm; k = 0.27 yr -1 for Sarotherodon galilaeus; and L∞ = 18.38 cm, K=0.55 year -1 for Tilapia zillii. The respective values of the total mortality coefficient Z were found to be 3.38, 2.94, 1.02 and 2.26 yr -1 . Moreover, their respective natural mortality coefficients M were 1.04, 1.21, 0.71 and 1.21 yr -1 . The estimated exploitation rates E were 0.69, 0.59, 0.31 and 0.47 in respective for the mentioned species. Their relative yield and relative biomass per recruit showed that the stock of O. niloticus and O. aureus were over the exploited. To obtain the maximum relative yield per recruit; the present level of exploitation rate should be reduced by about 20 % for O. niloticus and 10 % for O. aureus. The stocks of S. galilaeus and T. zillii were under the exploitation level.