Sexual Maturity, Fecundity, and Sex Ratios of the Skipjack Tuna, Katsuwonus pelamis (Linnaeus), in North Carolina Waters

Abstract

Abstract Sexual maturity, gonad index relationships, size at maturity, histology of gonadal changes, ova diameter frequencies, fecundity, and sex ratios were determined for skipjack tuna, Katsuwonus pelamis (Linnaeus), from Hatteras and Oregon Inlet, North Carolina. Minimum lengths of sexually mature fish were 435 mm and 454 mm for males and females, respectively. Fifty percent of the females were sexually mature at 500 mm long. Gross and microscopic examination of gonads along with gonad indices demonstrated that late June and early July were peak spawning times. Histological sections of gonads validated the stages of sexual maturity as determined from field examination. The ova diameter frequency of a nearly ripe fish showed three distinct modes: 0.15 mm, 0.50–0.60 mm, and 0.95 mm. Multiplicity of ova diameter modes and the presence of residual ova in fish with a new ripening group of ova demonstrated that skipjack tuna are multiple spawners. Fecundity estimates indicated that a fish 498 mm long spawns ...