REPRODUCTION, GONAD HISTOLOGY, AND SPAWNING CYCLES OF NORTH-ATLANTIC BILLFISHES (ISTIOPHORIDAE)

The gonads of 498 istiophorid fishes. mostly from the western North At lantic Ocean, were examined histologically. Female sailfish (Istiophor us platyterus), white marlin (Tetrapturus albidus), and blue marlin (M akaira nigricans) may spawn up to four times during their sexually act ive reproductive seasons. Males of all of these species can spawn thro ughout the year. Histologically, the only difference among the above s pecies and other istiophorids examined - black marlin (M. indica), str iped marlin (T. audax), and longbill spearfish (T. pfluegen) - 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 ovaria n follicles. Indications of previous spawnings are the presence of rup tured ovarian follicles and resorbing ovulated ova. Based upon our his tological studies, and on macroscopic field analyses and occurrence of larval stages reported in the literature, the following spawning seas ons and weights at first maturity of the female are as follows: sailfi sh (April through October; 13-18 kg), white marlin (March through June ; 20 kg), blue marlin (July through October; 120 kg), and longbill spe arfish (November to May; 17-19 kg).