Taylor et aL: Age, growth, maturation, and sex reversal in Centropomus undeamalis 



617 



Because scales were difficult to interpret, we were unable 

 to obtain consistent readings. Ages determined from scales 

 were always younger than ages determined from sectioned 

 otoliths by 1 to 3 years for snook less than 10 years. We 

 were unable to reach agreement for the ages of the ten 

 older snook whose structures were compared. Because of 

 the difficulties in interpreting the banding patterns on 

 scales, we did not attempt to analyze counts derived from 

 scales. 



The oldest common snook in our sample was a 21-year- 

 old, unsexed (i.e. sex not determined), east coast fish that 

 was 890 mm long (Table 2). This fish was identified as 

 a male in the field but because no gonad sample was 

 taken, we could not confirm the sex of the fish by histo- 

 logical analysis; consequently, we considered the fish to be 

 of undetermined sex in all analyses. The oldest east coast 

 male, other than the unconfirmed 21-year-old fish, was 15 

 years old (865 mm); the largest east coast male was 908 

 mm long and 11 years old. The oldest east coast female 

 was 18 years old (1025 mm), and the largest east coast 

 female was 1105 mm long and 16 years old (Table 2). The 

 oldest west coast male was 12 years old (810 mm), and the 

 largest west coast male was 925 mm long and 4 years old. 

 The oldest west coast female was 15 years old (982 mm), 

 and the largest west coast female was 1032 mm long and 

 10 years old (Table 3). 



Common snook grew rapidly until age 5-7 years after 

 which growth slowed considerably ( Fig. 6 ). The most abun- 

 dant age classes of males were from 2 to 7 years old and 

 those of females were from 3 to 8 years old (Tables 2 and 

 3). Only 10 east coast specimens were estimated to be 

 older than 16 years, and no west coast fish were older 

 than 16 years. The smallest and youngest female was a 

 397-mm west coast fish estimated to be 1 year old (Table 

 3). On the east coast, the smallest and youngest female 

 was a 448-mni fish estimated to be 2 years old (Table 2). 

 The sex-specific age-frequency distributions for the two 

 coasts were significantly different, and east coast fish were 

 older overall than west coast fish (Kolmogorov-Smirnov 

 two-sample, P<0.05). The coast-specific differences in age 

 were more pronounced for females than for males (Table 2, 

 Fig. 2). 



The von Bertalanffy growth models suggest that east 

 coast fish grow more rapidly than do west coast common 

 snook (Fig. 6, Table 4). Results of likelihood-ratio tests 

 showed a significant difference in the overall von Berta- 

 lanffy growth models for east coast and west coast snook 

 (;t'2=284.90, df=3. P<0.001). East coast estimates of K = 

 0.24, (95^/^ confidence interval=0.22-0.25) and /,, = -0.10 

 (95'7fCI=-0.01-(-0.19)) were significantly different from 

 west coast estimates of /C=0.18 (95'^^, CI=0.14-0.21) and 

 tQ = -1.35 OS'/f CI=-1.68-(-1.01)), (P<0.005, P<0.001, 

 respectively). The east coast estimate of L. 989 mm (95'7f 

 CI=966-1012) and 947 mm (957f 01=884-1010) for west 

 coast fish were similar (P=0.342). For fish ages 1-2. the 

 observed lengths at age of west coast fish were greater 

 than those of east coast fish, but for fish in most of the 

 older age classes, lengths of east coast fish were greater 

 (Tables 2 and 3). Lengths at age predicted from the von 

 Bertalanffy growth model for ages 0-2 were greater for 



Centropomus undecimalis 



Male - Tag #1307 



Tagged and Injected: 8/27/90 - 460 mm FL 



Recaptured: 8/7/97 - 492mm FL 



Figure 3 



A transverse section of an otolith from an age-9 common 

 snook, Centropomus undecimalis, that was injected with 

 oxytetracycline (OTC) on 27 August 1990 and released at 

 the entrance to Bishop's Harbor in lower Tampa Bay, Flor- 

 ida. The fish was recaptured 6 years and 11 months later 

 at the same location and had formed seven annuli between 

 the OTC mark and the otolith's edge. 



west coast fish than for east coast fish, but those for all 

 older age classes were greater for east coast fish than for 

 west coast fish. 



Maturation and sex transition 



Common snook present biological characteristics that are 

 consistent with protandric hermaphroditism. We exam- 

 ined 27 wild-caught specimens that we considered were 

 at the transitional-sex stage on the basis of simultaneous 

 presence in the gonad of ovigerous lamellae and rem- 

 nants of the dorsal sperm ducts that contained sperm. 

 The mean length and age of these transitional-sex-stage 

 common snook were 515 mm and 3.4 years. They ranged in 

 length from a 240-mm, 1-year-old male specimen that had 

 a prodigious number of ova in the peripheral portions of 

 the testis, to an 824-mm, 7-year-old female with residual 

 sperm in remnant sperm ducts. All ovaries, transitional 

 and otherwise, contained remnants of the major dorsal 

 sperm ducts, regardless of season or reproductive condi- 

 tion (Fig. 7). In addition, transitional gonads contained 

 degenerating spermatogenic and developing ovarian tissue 



