Abstract

• A total of 692 clams (319 were males and 373 were females) were analyzed. Six different gonad development stages in both males and females were identified. The average gonads socratic index (GSI) value of males was high in May and November (2.02 ±0.6 and 1.88 ±0.7). In females, the maximum GSI value was observed in May and November (1.80 ±0.6 and 1.75 ±0.5). The monthly changes in the gonadosomatic index and the microscopic characteristics of ovaries showed that G. expansa was recorded as two times spawning periods, the majority of spawning periods were recorded in the summer months of May, June, and July, and the second spawning (minor spawning) took place in or around November. The present results indicated that G. expansa is dioecious and gametogenic development was synchronous between the sexes. Temperature is the major factor in controlling the reproductive cycle in G. expansa.