Study of the reproductive biology of the Lessepsian migrant pufferfish species Lagocephalus sceleratus was carried out for two different populations; the first representative the native population in the Gulf of Suez (Red Sea), while the other one representative to the migrant population in the Egyptian Mediterranean Sea. The samples collected seasonally for two populations from winter 2013 till autumn 2014. The sex ratio (Males: Females) throughout study period were found 1:1.07 and 1: 1.29 for Gulf of Suez and Mediterranean population respectively. Males matured earlier in life than females in both study areas. For Gulf of Suez population, the fish length at first sexual maturity (L50) was 36.3 cm for males and 37.1 cm for females, while forMediterranean population the fish length (L50) were 32.5 and 36.3 cm for males and
females respectively. Accordin g to the present results of seasonal variations in maturity stages and Gonado Somatic Index (GSI) the reproductive season of Lagocephalus sceleratus collected from Gulf of Suez and Alexandria, Egyptian
Mediterranean waters exhibits a relatively prolong spawning season extending from spring to summer for both sexes. In the current study, the absolute fecundity of L. sceleratus, for both study areas, increased with increasing in length and weight. The relative fecundity also showed slightly increase with the increase in length, while it showed small fluctuations combined with decrease particularly of largest weight fish groups with the increase in total weight.