Egyptian beaches have extended over long distances and it has become necessary to look at how the exploitation of bivalves inhabiting these beaches. Onset of sexual maturity for 7 bivalve species in 4 sites of Egyptian waters was reported. Specimens were collected during summer and winter seasons. A total of 1870 individuals belonging to 4 families were examined under the microscope. The trend of decreasing size at maturity with increasing water temperature was reported. The trend of increasing size at maturity with decreasing latitude was much less clear in this study. The size at 50% maturity (SM50) varied between 9.2 mm SL (for Cerastoderma glaucum in summer) and 16.6 mm SL (for Venerupis aurea in winter), and showed an average value of 12.7 mm SL (± 2.4 S.D.) for 5 commercial clams.
