Reproduction, Gonad Histology, and Spawning Cycles of North Atlantic Billfishes (Istiophoridae)

The gonads of 498 istiophorid fishes, mostly from the western North Atlantic Ocean, were examined histologically. Female sailfish (Istiophorus platypterus), white marlin (Tetrapturus albidus), and blue marlin (Makaira nigricans) may spawn up to four times during their sexually active reproductive seasons. Males of all of these species can spawn throughout the year. Histologically, the only difference among the above species and other istiophorids examined—black marlin (M. indica), striped marlin (T. audax), and longbill spearfish (T. pfluegeri)—was in the size of the ova, which is smallest in the sailfish and largest in the blue marlin. The number of previous mature generations of ova can be ascertained by the different stages of involution of atretic ovarian follicles. Indications of previous spawnings are the presence of ruptured ovarian follicles and resorbing ovulated ova. Based upon our histological studies, and on macroscopic field analyses and occurrence of larval stages reported in the literature, the following spawning seasons and weights at first maturity of the female are as follows: sailfish (April through October; 13–18 kg), white marlin (March through June; 20 kg), blue marlin (July through October; 120 kg), and longbill spearfish (November to May; 17–19 kg).