Taylor et al.: Age, growth, maturation, and sex reversal in Centropomus undecimalis 



623 



males we observed were smaller than those observed by 

 previous workers; however, previous studies of maturation 

 were based only on a macroscopic examination of gonads. 

 Marshall ( 1958) examined 239 common snook from south- 

 west Florida and concluded that 50'r of the specimens of 

 both sexes were mature at 400 mm and that all common 

 snook, with few exceptions, were mature at 500 mm. Volpe 

 (1959) used Marshall's lengths-at-maturity data to esti- 

 mate the age at first maturity to be 3 years. It is unclear 

 whether the small males we observed were spawning 

 males, but they appeared to be capable of spawning; there- 

 fore we considered them to be sexually mature. Common 

 snook typically spawn in large aggregations near passes 

 and inlets (Taylor et al.. 19981. We did not obsen-e males 

 smaller than 350 mm in spawning aggregations, and most 

 spawning males were longer than 400 mm; however, we 

 can not eliminate the possibility that some spawning 

 involved smaller males outside these large aggregations. 

 Additional research is needed to determine whether or not 

 these small, precocious males are active members of the 

 spawning population. 



We considered all female common snook to be sexually 

 mature on the assumptions that they develop directly from 

 males that had previously spawned, that sex transition 

 occurs shortly after spawning, and that they would be capa- 

 ble of spawning as females during the next spawning season. 

 Among other centropomids, L. calcarifer also undergoes sex 

 change near the end of the spawning season (Davis, 1982; 

 Guiguen et al., 1994). Davis (1982) found that in L. calcari- 

 fer, oocytes first appear as the testes ripen for the final time 

 and that sex reversal is completed shortly after spawning. 

 This finding is consistent with our observations of common 

 snook. Most transitional-sex-stage individuals were captured 

 during September-November; we did not observe any tran- 

 sitional fish from April to June and only one transitional fish 

 in February and one in March. Sex reversal appears to occur 

 quickly and shortly after spawning, and we found no evi- 

 dence to suggest that females do not spawn during their first 

 spawning season after transition from male to female. This 

 conclusion is supported by the captive fish that completed 

 sex reversal and developed vitellogenic oocytes in only two 

 months. Management decisions based on length and age at 

 maturity of females should more appropriately focus on the 

 size and age at sex transition, and all females should be 

 included in estimates of spawning stock biomass. 



Acknowledgments 



We thank the many anglers and biologists who partici- 

 pated in this study. We especially thank Ed Irby, Kraig 

 Krum, William Howard, and other staff at the Tequesta 

 field laboratory. Iliana Quintero, Pamela Nagle, and Ruth 

 Reese provided invaluable assistance. Buck Dennis, Wil- 

 liam Halstead, John Young, Patricia Hindle, and other staff 

 at the Stock Enhancement Research Facility are kindly 

 acknowledged. We thank David Harshany, Doug Haymans, 

 Dan Merryman, Heather Patterson, Graham Gerdeman, 

 and Connie Stevens for their assistance. This manuscript 

 was greatly improved by the conscientious reviews of Jim 

 Quinn, Judy Leiby. and Llyn French. This work was sup- 

 ported in part under funding from the Department of the 

 Interior, U.S. Fish and Wildlife Service, Federal Aid for 

 Sportfish Restoration, Project Number F-59. 



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