Red grouper reproduction in the southern Gulf of Mexico

The reproductive biology of red grouper Epinephelus morio from the inshore and offshore waters of the Yucatan Peninsula (Campeche Bank) was investigat ed over a 5-year period (1988-1993). Results confirmed that red grouper is a monandric protogynous hermaphrodite as shown by (1) the absence of primar y males in samples, (2) the presence of transitionals in the population (1% of the total offshore catches), (3) the occurrence of a membrane-lined cen tral cavity in the testes of all males and dorsal sinuses in the gonadal wa ll in most males, (4) the significant difference in size ranges and mean fo rk lengths of males and females, and (5) a female-biased male:female ratio in size-classes less than 72.0 cm fork length (PL). We found immature femal es all year round in inshore waters and immature females, mature females, a nd males, and transitionals in offshore waters. In the southern Gulf of Mex ico, the species displayed seasonal reproduction, with single, annual peak spawning occurring in late winter and early spring (January-March). The gre atest variations in the mean gonadosomatic index (GSI) of females were reco rded between November (0.27%), February (2.14%), and April (0.17%) when the y were ripening, ripe-running, or spent. Males were ripening between Septem ber and February, ripe-running from December through April, and spent in Ma rch. Spawning aggregations of red grouper were not observed. However, durin g the 1992 spawning period, 20 ripe-running females and 19 ripening and rip e-running males were caught near 20 degrees 47'N, 91 degrees 40'W on the we stern Campeche Bank on the second and fourth days after full moon, Sexual m aturation in females occurred over a broad size range (38.9-72.0 cm FL). Th e size at first maturity, defined as length at which 50% of females were se xually mature (L50), was 50.9 cm FL =/- 1.2 (mean +/-SE). Sex inversion in females did trot occur at a particular size or at a precise time. Size rang e and median size at which females change sex were 41.0-85.4 cm FL and 59.7 cm FL, respectively. Transitionals were caught during 5 months of the year , including two peak spawning months (January and February). Fishery manage ment implications are presented and discussed.