We describe the prey, seasonal patterns of feeding, and coelomic fat mass storage in a tropical population of the diamondback watersnake (Nerodia rhombifer werleri) and relate these data to the reproductive cycle of the studied population. Snakes were collected on the Papaloapan River, nearby lagoons, and as road kill near Tlacotalpan, Veracruz, Mexico in 1987. Diet and feeding frequency were determined by stomach content analysis of preserved snakes. The diet consisted primarily of fish (seven identified species belonging to six families). Of the adults examined, 21% of the 95 males and 32.5% of the 77 females contained food. In all age and sex classes of snakes, the feeding frequency did not differ between the wet and dry seasons. For adult males and adult females, coelomic fat mass was higher in February, March, and April than in other months. The variation in mass of the fat bodies was greater in adult females than in adult males. In females, low fat reserves may account for the low frequency of reproduction and the small litter sizes found in our studied population. In males, low fat reserves are correlated with decreased size of the diameter of the seminiferous tubules and the sexual segment of the kidney.