A total of 245 individuals from a population of the endemic Bermuda killifish Fundulus bermudae in an isolated anchialine pond (Mangrove Lake) were trapped between November 2004 and November 2005. Laboratory analysis of gonad development allowed determination of the seasonal reproductive cycles of both females and males. A distinctive annual pattern was evident, with female and male gonadal cycles synchronous throughout the study period. The results indicate that the F. bermudae males and females began their spawning season in February, but reached primary peaks in May and June respectively. Gonadal indices abruptly fell after June and continued to fall at a steady rate until September, marking the end of the spawning season. Gonad recrudescence, as indicated by basal gonad indices, occurred in September and lasted throughout the autumn and early winter months.