Gonadal activity in some Bottlenose dolphins ( Tursiops truncatus )

Details are given of the characteristics of the ovaries and testes of young and adult dolphins, Tursiops truncatus , all of which had been caught off Florida or Mississippi. Most had been in captivity for periods varying from a few days to ten years. Birth takes place most commonly during February to May and September to November. Length of neonates is between 98 and 126 cm. The state of activity of the gonads suggests that sexual maturity is reached in females at a length of over 220 cm and probably in their fifth year. Males do not become sexually active until about 260 cm in length and at an estimated age of at least ten years. Plasma testosterone levels are highest in a captive fertile male during April and May and October and November. The corpus luteum persists throughout the 12‐month gestation period and also appears to persist as a corpus albicans for the dolphin's life span. The left ovary is usually larger than the right and twice as many corpora are found in the left as in the right ovary. No evidence of regular, cyclic ovulation is detected and it is concluded that ovulation is induced in Tursiops.