I n the River Nile from Giza to Assuit, males of Synodontis schall attain their first sexual maturity at smaller size and slightly earlier age compared to females. The estimated survival rate of the population was 35% per year. The current exploitation of S.schall was computed to be 0.52. Simulation analysis of production per biomass (P/B) was made to evaluate changes that may occur if the fishing pressure increased or decreased. P/B ratio of juvenile S.schall increases with increase of the

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... ing effort , while the reverse is the case for adult population. Maximum Sustainable Yield {MS Y) was predicted to occur at 0.5 fishing mortality coefficient, where this level of exploitation would be expected to cause a shift toward larger sizes of fish and virtually eliminate fish in the small size-classes (immature fishes).