622 



Fishery Bulletin 98(3) 



approximately one meter may be a result of the difficulty 

 of sampling large robust snook; trophy-size individuals are 

 not uncommon in Florida and snook 1155-1194 mm are 

 recorded (IGFA, 1998). 



Maturation and sex transition 



We based our determination that common snook are pro- 

 tandrous hermaphrodites on the following criteria pre- 

 sented by Sadovy and Shapiro ( 1987): 1) sex ratios shifted 

 from exclusively male to predominantly female with 

 increasing size and age, 2) transitional-sex-stage individu- 

 als were observed whose gonads contained both degener- 

 ating spermatogenic and developing ovarian tissue, and 3 1 

 sex change was documented in captive fish. Common snook 

 have not previously been diagnosed as protandrous her- 

 maphrodites, but another centropomid, the barramundi 

 Lates calcarifer, has been diagnosed as a protandric her- 

 maphrodite (Moore, 1979; Davis, 1982). 



The male-to-female sex ratios previously reported for 

 southwest Florida common snook (e.g. Volpe 1959, Thue et 

 al.,1982 ), are similar to ours, with the exception of those 

 reported by Marshall (1958). Thue et al. (1982) reported 

 a 3:1 sex ratio for common snook smaller than about 500 

 mm and younger than age 2 in the Everglades National 



Park and a sex ratio 1:11 for common snook larger than 

 800 mm and older than age 8. Volpe (1959) reported a 

 similarly skewed sex ratio of 1:3 for fish larger than 800 

 mm from southwest Florida. These shifts in the common 

 snook sex ratio with increasing length and age are consis- 

 tent with our diagnosis of protandrous hermaphroditism. 

 In contrast, Marshall (1958) found that there were more 

 females than males smaller than 500 mm (1.0:1.1) and 

 that the overall sex ratio for common snook in southwest 

 Florida was not significantly different from 1:1. It is pos- 

 sible that Marshall (1958) did not observe the actual sex 

 ratio of the population he studied because 288 of the 531 

 total specimens in his sample had been gutted and were 

 not included in the analysis. 



Male common snook reach sexual maturity at surpris- 

 ingly small lengths and ages, some at lengths less than 

 200 mm. We considered a fish to be sexually mature if 

 mature sperm were present in the testis. According to this 

 criterion, immature males made up <'2'/r of our sample. 

 Furthermore, most of the males we classified as immature 

 were caught outside of the spawning season, and we may 

 have misclassified some regressed mature fish as imma- 

 ture. Because our sample contained so few males that we 

 could be certain were immature, we did not attempt to 

 fit a logistic function to male maturity. The small mature 



