Seasonal variations in reproductive condition and fat content of cyprinodontids from eight populations in Florida and southern Texas were examined. In all species the spawning period is protracted. Cyprinodon variegatus may spawn throughout the year. Spawning in Fundulus similis apparently occurs during all months except November, December, and January, but is terminated during September in F. grandis. Cessation of spawning occurs during September in F. lineolatus, but during July in F. chrysotus. Adinia xenica may have a longer spawning season than the species of the Fundulus investigated. A seasonal variation in body fat content was observed in C. variegatus, A. xenica, F. grandis, F. lineolatus, and F. similis (from Texas, but not Florida). Maximum fat reserves and the seasonal variation in fat levels differed among the species studied. Seasonal variations in body fat content and gonadal size were not correlated in any of the species. Seasonal changes in standing crops of zooplankton and phytoplankton were compared to annual variations of body fat content and gonadal size in C. variegatus and F. similis from Texas. Neither gonadal size nor fat content correlated with zooplankton or phytoplankton standing crops.