We describe the life history of yellowmouth grouper, Mycteroperca interstitialis, using specimens captured at the Florida Middle Ground in the eastern Gulf of Mexico between May 1978 and July 1992. Spawning occurred throughout the year; peak activity was observed during April
and May. Yellowmouth grouper are protogynous hermaphrodites: sex-inversion was documented for five individuals, younger/smaller individuals were female, and most older/larger fish were male. Females began to mature at 400 mm total length (TL) or age 2; all were mature by 450 mm or age 4. Transitional
fish ranged 505–643 mm and were 5 to 14 years old. The smallest and youngest mature male was 505 mm and age 4. Ages could be readily determined from otolith sections because they contained distinct opaque bands that formed during the late summer and fall. Females ranged 2 to 17 years
old; males were 4 to 28 years of age. Annual growth of yellowmouth grouper averaged greater than 200 mm or 470 g during their first 2 years of life and then slowed thereafter to about 18 mm or 221 g for females and to about 10 mm or 190 g for males. Significantly different linear growth models
fit sex-specific length-at-age and weight-at-age data well. Length-age and weight-age relations for all fish were: It = 828 (1 − exp(–0.076(t + 7.5))) and wt = 13.9 (1 – exp(–0.022(t + 1.4))), where It is TL in mm, wt, is
weight in kg, and t is age in years. The pooled estimate of total annual mortality for ages 8–18 during 1978–1992 was about 25%. Because of similarities in their morphology and habitat preference, we compared our findings for yellowmouth grouper with life-history aspects of its
closely related congener, the scamp (M. phenax).
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