Abstract

Tripletail, Lobotes surinamensis, is a large pelagic fish that is becoming increasingly popular with recreational anglers throughout the Gulf of Mexico. There is, however, little information on the biology of this species and virtually nothing is known regarding the reproduction of tripletail. We examined tripletail captured from the northern Gulf of Mexico in the spring and summer between July 1994 and September 1999 to determine size at sexual maturity and reproductive patterns. No sexually immature male tripletail were captured during the course of the study. The size at 50% maturity for female tripletail is 485 mm TL. corresponding to an estimated age of one year. Mean monthly female gonadosomatic index (GSI) values were elevated throughout the summer, highest in July and near resting levels by September. Male GSI values were elevated from May through September. Histological analysis of gonadal tissue from 93 male tripletail showed the majority of males captured from May through September were running ripe. However, active spermatogenesis declined in the test is during the course of the reproductive season. Analysis of gonadal tissue from 118 females provides evidence that tripletail are a multiple spawning species. Females were found in the late developing ovarian maturation stage from June through August; regressed and spent females were captured from June through September. A high percentage of females captured during April, May and June were in the immature and early developing ovarian maturation stages. Females with oocytes undergoing final oocyte maturation (FOM) were found June through August, with the highest percentage in July. Thus, tripletail appear to have a three month spawning season in the northern Gulf of Mexico, with July the peak: spawning time. However, most reproductively active female tripletail appear to remain well offshore. Estimates of batch fecundity, based on five tripletail undergoing FOM in July suggest fecundity is positively correlated with length; mean relative batch fecundity was 47.6 eggs/g ovary-free body weight. Preliminary estimates of spawning frequency, based on the percentage of females in the late developing ovarian stage undergoing FOM or containing postovulatory follieles during June through August, suggest that female tripletail are capable of spawning once every three days to five days in the northern Gulf of Mexico.

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