Brule et al. : Reproduction in Mycteroperca bonaci 



469 



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Figure 4 



Individual and mean gonadosomatic index (GSI) values for female and male black grouper, (Mycteroperca bonaci) collected 

 in offshore waters of the Campeche Bank, Mexico, between April 1996 and May 1999. All calculated GSI for this study were 

 grouped to show monthly variations over a single year Vertical bars denote standard error. Numbers above the bars denote 

 the sample sizes. 



grouper from the Campeche Bank are consistent with the 

 description of monandric protogynous hermaphroditism 

 previously used for this species. During the present study, 

 three of the five criteria suggested by Sadovy and Shapiro 

 (1987) for identifying protogyny in hermaphroditic fishes 

 were identified in black grouper: membrane-lined central 

 cavities in testes; sperm sinuses in the gonadal wall; and 

 transitional individuals. The five black grouper specimens 

 considered as transitional individuals (0.6% of sampled 

 offshore fish ) did not have degenerating ovarian tissue in 

 their gonads. For protogynous species, the degeneration of 

 ovarian tissue should logically accompany proliferation of 

 testicular tissue for the specimen to be termed "transi- 

 tional." However, according to Sadovy and Shapiro (1987), 

 the paucity of reported cases providing such descriptions 

 raises doubts as to whether transitional gonads display 

 this kind of histological profile. These observations also 

 may be a function of the fact that the incidence of tran- 

 sitional fish in field collections is generally relatively low, 

 as shown by the single transitional specimen (0.1% offish 



collection) identified by Crabtree and Bullock (1998) in a 

 sample of the Florida black grouper population. Precocious 

 spermatocyte or sperm cysts in immature or functional 

 ovaries as observed by Smith (1964; 1965) and Bullock et 

 al. (1996) in coney (Cephalopholis fulva), graysby (Cepha- 

 lopholis cruentata ), and yellowedge grouper iEpinephelus 

 flavolimbatus) were not found in black groupers ovaries 

 during our study. 



Other aspects of population structure indicating mo- 

 nandric protogynous hermaphrodism were also seen in M. 

 bonaci from the Campeche Bank. These included bimodal 

 size-frequency distributions, where males were larger than 

 females, female-biased sex ratios in size classes less than 

 1 10. 1 cm, and male-biased ratios in size classes larger than 

 115.0 cm. No male smaller than 86.0 cm was identified in 

 any of the samples. Despite these biases, the overall male- 

 to-female sex ratio calculated in our study (1:4) was less 

 skewed towards females than those reported by Garci'a- 

 Cagide and Garcia (1996) (1:30.3) and Crabtree and Bull- 

 ock (1998) (1:15.4). Notwithstanding, the sex ratio for black 



