Growth, mortality and relative yield per recruit of the sharptooth catfish clarias gariepinus (Clariidae) in Lake Manzalah, Egypt

Abstract

Clariid catfishes are of great economic importance as protein food in adequate prices. For several years, species of the genus Clarias (Scopoli, 1777) have been used in local fish culture, where they proved to be a fast growing protein source. Age, growth, mortality and relative yield per recruit of Clarias gariepinus in Lake Manzalah, Egypt, were investigated. The maximum life span based on otoliths’ readings was 8 years, while the von Bertalanffy growth parameters were L∞= 86.88cm, K= 0.31/year and t 0 = -0.39 year. The mean annual instantaneous total, natural and fishing mortality coefficients were 0.98, 0.37 and 0.61/year, respectively. Accordingly, the exploitation ratio was 0.62, which was higher than the optimum one. Relative yield per recruit analysis revealed that C. gariepinus is over exploited in Lake Manzalah where the E 0.5 was lower than the current one (E 0.5 = 0.35). Some recommended management actions should be applied to strengthen the ban of fishing in the spawning season or in the nursery ground and to adopt a legal minimum size to protect the young and small-sized fish. In addition, to make any regulation more effective, all stakeholders (fishermen, scientists, non-governmental organizations and policy makers) should work together to establish a comanagement plan to conserve this valuable stock.