In the present investigation, age, growth, mortality, exploitation, yield and biomass and
reproduction of Nile tilapia (Oreochromis niloticus) from El-Bahr El-Faraouny Canal, Al-Minufiya
Province, Egypt, were determined. The regression parameter “n” of dependence of total weight upon
total length was found to be negative allometric growth. The coefficients of condition were
computed. The annual rings on fish scales were used for age determination. The longevity of this
species was found to be 6 years. The maximum increase in length was noted during the first year
of life and showing a gradual decrease in growth as the fish got older. The O. niloticus population
had a sex ratio of 1:1.08 (M:F), which did not deviates (χ2 = 1.997, p>0.05) from the hypothetical
distribution of 1:1. The maturity stages were classified macroscopically into five stages. Higher
values of gonadosomatic index (GSI) for males and females occurred nearly throughout the year
with peak from May to August indicating prolonged spawning season. There is a selective mortality
towards smaller fish sizes. Therefore, for management purposes it is recommended that the local
authorities must be set a regulation to control the illegal fishing activity and larger mesh sizes of
fishing nets should be used to increase the mean lengths at first capture and their marketable sizes
leading to more economic returns and also to conserve the spawning stock part of O. niloticus
population. A comparison of the various parameters of O. niloticus in the present study with those
of other authors in different localities and times in Egypt revealed year-to-year and geographically
differences. These differences were discussed and were found to be attributed to the effect of
increased pollution of the canal. Finally, the present study recommended that El-Bahr El-Faraouny
Canal must be in protection against pollution |
