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



621 



may reflect sampling bias rather than a true differ- 

 ence in the maximum fish sizes reached on the two 

 coasts. 



Other comparative studies on two inshore ( Flor- 

 ida) Sciaenidae species also have found that east 

 coast fishes attain greater sizes or grow at faster 

 rates than do west coast fishes (Murphy and Taylor. 

 1990; Murphy and Taylor, 1994). Although gear 

 biases may have confounded growth differences in 

 these comparative studies, there is some basis for 

 physiological differences in common snook. Trin- 

 gali and Bert (1996) have provided evidence that 

 common snook in Florida comprise two geneti- 

 cally different populations: one population in Atlan- 

 tic waters and one in Gulf waters. They have 

 reported that mtDNA divergence, both in haplo- 

 type diversity and in nucleotide sequence, supports 

 the hypothesis that the two populations are repro- 

 ductively isolated, which may account for a portion 

 of the observed differences in biological parame- 

 ters. 



Age and growth 



Our findings suggest that scales and whole otoliths 

 may not be suitable for aging common snook older 

 than 6-9 years, the point at which our length-at- 

 age data began to reach an asymptote. Ages derived 

 from whole otoliths were reasonably accurate for 

 snook younger than about 10 years, but ages of older 

 snook were consistently underestimated. Further- 

 more, whole otoliths were more difficult to read than 

 sectioned otoliths and therefore readers' counts from 

 whole otoliths often varied, principally because the 

 closely spaced annuli on the edge of whole otoliths 

 were difficult to differentiate. Our observations of 

 common snook scales led us to conclude that they 

 were not suitable for use in age estimation. Whole- 

 otolith-derived estimates of longevity reported by 

 Volpe ( 1959 ) and scale-derived estimates by Thue et 

 al. ( 1982 ) of 7-8 years are considerably less than our 

 sectioned-otolith-derived estimate of 21 years. Both 

 Volpe ( 1959 ) and Thue et al. ( 1982 ) examined fewer 

 fish than we did: therefore their samples would be 

 expected to contain fewer old individuals than ours 

 did. Their samples were also collected many years 

 before ours, and additional regulations have been 

 imposed on the fishery since their studies; however, 

 the magnitude of the discrepancies in ages between 

 our study and theirs is so great that we suspect 

 they underestimated the ages of many fish. Thue et 

 al. (1982) reported von Bertalanffy growth param- 

 eters for common snook, but their growth model did 

 not reach an asymptote; consequently, their esti- 

 mate of L = 1615 mm for combined sexes is much 

 greater than our estimate for either coast and is far larger 

 than the length reported for any common snook. We suspect 

 that their growth curve did not reach an asymptote because 

 they consistently underestimated the ages of old common 

 snook. 



DBV 



N 



BV 



SD 



BV 



• .« 



Sdc 



OL 



Figure 7 



A histological section from a transitional-sex-stage common snook, 

 Centropomus undecima/is (632 mm FL). captured in lower Tampa 

 Bay in July 1989. Remnants of the major sperm duct (SD) and 

 collecting tubules (*) are present in the dorsal matrix. Located 

 throughout the peripheral ovigerous lamellae (L) are female germ 

 cells that are either primary growth oocytes (OC) or meiotic and 

 interphase oogonia (arrows). The dorsal (DBV) and lateral (BV) 

 blood vessels are distinguished from the sperm ducts by the pres- 

 ence of red blood cells. OL = ovarian lumen. 



Growth data for common snook in our study fitted the 

 von Bertalanffy model well. The poor fit at age for the 

 east coast is explained by the collection of young-of-the- 

 year fish in April and May, just prior to their first birthday 

 when they were longest at age. The asymptotic values of 



