468 



Fishery Bulletin 101(3) 



rence in January (28%) and February (52%)(Fig. 6B). The 

 gonads of 50 ripe-running females caught between Janu- 

 ary and April, and during June and November, contained 

 both postovulatory follicles and stages III-V vitellogenic 

 oocytes without sign of degeneration (Fig. 6C). Spent fe- 



Figure 3 



Photomicrographs of histological sections from male and 

 transitional black grouper iMycteroperca honati) gonads 

 collected from Campeche Bank, Mexico. (A) Section from a 

 1 14-cm-FL ripening male captured in July 1997, showing 

 lamellae, lumina, spermatogonia, and spermatocyte cysts, 

 and lamellae sinuses full of spermatozoa. (B) Section from a 

 r2'2-cm-FL ripe-running male captured in September 1997, 

 with sperm sinus full of spermatozoa in gonadal capsule. 

 (C) Section from a 113-cm-FL transitional fish captured in 

 January 1998, showing previtellogenic oocytes (stages I) 

 and scattered spermatocyte cysts. CX' = gonadal capsule; L = 

 lumen; LA = lamellae; PO = previtellogenic oocyte; SPC = 

 spermatocyte; SPG = spermatogonia; SPZ = spermatozoa; 

 SS = sperm sinus. Scale bars = 200 microns. 



males, with atretic and remaining vitellogenic oocytes in 

 their gonads, were caught between January and August 

 {3-297f ). Resting mature females, with stages -I and -II oo- 

 cytes, bundles of muscle, and yellow bodies in their ovaries 

 were abundant in samples taken from May to November 

 (54-98%). Ripening or ripe-running males were recorded 

 year-round and spent males were observed in November 

 (4%), from January to March (10-40%), and from May to 

 July (8-22%). 



Various females from the Alacranes Reef were ripening 

 in November (GSI range: 0.03-4.44%, n=l2), December 

 (GSI range: 0.22-7.18%, n=9) and February (GSI range: 

 0.10-6.61%, n=25). In February, some of them were ripe- 

 running, with postovulatory follicles in ovaries (GSI=1. 77% 

 and 1.91%, n=2) and others were spent (GSI=0.74% and 

 0.88%, n=2). Alacranes Reef males were ripening or ripe- 

 running in November, December, and February (GSI range: 

 0.03-0.44%, «=11). 



Location and timing of spawning 



Between April 1996 and February 2000, 61 ripe-running 

 females were caught at 11 offshore fishing locations situ- 

 ated in the northeastern part of the Campeche Bank (depth 

 range: 51-68 m), and from shallow waters of the Alacranes 

 Reef (8-10 m) (Fig. 1). All had vitellogenic oocytes (stages- 

 III-V) with hyaline oocytes or postovulatory follicles (or 

 with both) in their ovaries. Most of these females were 

 caught during, or close to, the new moon phase (Table 2). 



Sizes at maturity and at sexual transition 



The smallest mature female (L^j|jj=58.0 cm) was caught 

 in shallow waters of the Alacranes Reef and had stage-Ill 

 oocytes in its ovaries. Fifty-percent maturity of females 

 was attained at 72.1 cm in size and all females larger than 

 95.1 cm were mature (Fig. 7). Because the largest female 

 observed in samples was 123.5 cm (L^,^^), the percentage 

 of females at maximum length at first maturity was l^„^,J 



Females changed sex between 85.5 and 125.0 cm in 

 length (the overlap zone between male and female sizes) 

 and the median size of sexual inversion was 103.3 cm. By 

 the time they attained a length of 111.4 cm, 50'7f of the 

 females in the sample had transformed into males (Fig. 8). 

 Size range of transitional fish (99.0-121.5 cm) was 17% of 

 maximum fish size ( 135.0 cm) (ratio 1, see "Materials and 

 methods"'section), and sex change occurred over 29'7f of the 

 maximum size observed for the species (ratio 2). Immature 

 males were not observed during the study. 



Discussion 



Sexual pattern 



Previous research strongly suggests that sex reversal 

 occurs in M. bonaci (Smith, 1959, 1961; Garcia-Cagide and 

 Garcia, 1996; Crabtree and Bullock, 1998). Observations on 

 gonadal and population structure characteristics for black 



