466 



Fishery Bulletin 101(3) 



140 

 120 

 100 • 



80 



60  



40 



20 



E 



D Female (inshore waters) 



D Female (offshore waters) 



^tt^aie 



 Transitional 



-P-P- 



P r fn ,1 1 ,l, i , 1 , 1 , H , 11 JL .i k .l b ^ 



20 30 40 50 60 70 80 90 100 110 120 130 



20 



50 60 70 80 90 

 Fork length (cm) 



100 110 120 130 



Figure 2 



Size-frequency distribution for females, transitional individuals, and males for 

 black grouper {Mycteroperca bonaci) caught between April 1996 and February 

 2000 in offshore and inshore waters of the Campeche Bank (A), and in shallow 

 waters of Alacranes Reef (B), Mexico. 



sex ratios were female-biased in size classes less than 

 110.1 cm, did not differ significantly from a 1;1 sex ratio 

 in the 110.1-115.0 cm size class, and were male-biased in 

 size classes larger than 115.0 cm. The overall black grouper 

 sex ratio was 1:4, which differed significantly from unity 

 (Xf-=400.8,P<0.05). 



Fin pigmentation 



Of the 104 black grouper analyzed to detect gender- 

 associated color changes, 98 were females (size range 

 47.0-99.0 cm), five were males (99.0-115.0 cm), and one, 

 which presented previtellogenic oocytes and nests of sper- 

 matocytes and spermatozoa in its gonads, was classified as 

 transitional (99 cm). All males, as well as the transitional 

 specimen, displayed the male color phase with jet black 

 pigmentation on pectoral, anal, and caudal fins. Only 59f of 

 the females (size range 50.0-100.0 cm, «=5) had jet black 

 pigments on their fins. 



Gonadal structure 



All ovaries presented a central cavity with a germinal epi- 

 thelium forming the surface layer of a series of projecting 

 ovigerous folds or lamellae of the tunica albuginea. 



Of the 225 males assessed histologically, 769f (;! = 170) 

 presented a membrane-lined central cavity in the testes. 

 This lumen remained unused in the transport of spermato- 

 zoa, and sperm ducts or sinuses within the gonadal capsule 

 were observed in ZT7< of the specimens (/;=84) (Fig. 3, A and 

 B). Previtellogenic oocytes (stages I and II ) remained in 

 the testes of 13''i of the males (?)=30), and only one of these 

 (107.0 cm) presented previtellogenic oocytes in degenera- 

 tion within lamellae in a fully developed testis dominated 

 by crypts of spermatocytes, spermatids, and spermatozoa. 

 Yellow bodies w(>re oi)sorved in the testes of 96'r of the 

 males. 



Internal gonadal structure for the five black gi-oupers 

 classified as transitional was very similar to that of im- 



