244 



Fishery Bulletin 90(2). 1992 



Methods and materials 



Jewfish were sampled aperiodically from recreational 

 and commercial catches from the eastern Gulf of Mex- 

 ico, November 1977 through January 1990. Fifty-six 

 percent (269/481) of the sampled jewfish were captured 

 using spearguns, 27% by hook-and-line, 8% by bottom 

 longline (either grouper/snapper or shark fisheries), 

 and the remaining 9% by shrimp trawl, trap, or un- 

 recorded methods. We attempted to determine sex, 

 whole (WW) and/or gutted (GW) weight (kg), and total 

 length (mmTL) for each specimen, although we could 

 not determine whole weight and sex when fish had been 

 eviscerated (A/" 271). Although eviscerated, unsexed fish 

 could not be included in our study of reproduction, they 

 were used in the age and growth analyses. If sagittae 

 could be located, they were removed from the otic cap- 

 sule (A'^ 384) and stored dry. A portion of the gonad, 

 if available (A'^ 173), was preserved in 10% formalin and 

 later transferred to 70% ethanol. 



Otolith sections were examined for evidence of age 

 marks. Transverse sections, approximately 0.5mm 

 thick, were cut from each sagitta with a Buehler Isomet 

 low-speed saw. Sections were mounted on microscope 

 slides with Histomount mounting media and examined 

 for age marks under a dissecting microscope using 

 reflected light. Age marks were counted independent- 

 ly by two readers. Later, a joint reading was conducted 

 in an attempt to resolve differences between counts. 



Monthly mean marginal increment ratios were cal- 

 culated for fish with 1-10 annuli to determine the 

 periodicity of mark formation. Marginal increment was 

 standardized for differences in growth among age- 

 classes by dividing the marginal increment for each fish 

 by the distance between its penultimate and outermost 

 annuli. We called this calculated value the 'marginal 

 increment ratio' (sensu percentage of marginal incre- 

 ment; Hood et al. Unpubl. manuscr.). Fish were as- 

 signed ages based on the number of annuli and a 

 biologically realistic hatching date of 1 September (time 

 of peak spawning; see Results). All fish were assigned 

 an age equal to their annulus count, except for fish 

 collected prior to 1 September and that had already 

 deposited an annulus during the most recent period of 

 mark deposition (April-August; see Results). The 

 assigned age for these fish was one less than their 

 number of annuli. 



Observations to determine the validity of age marks 

 were made from two jewfish (290 mmTL, 509g; and 

 375 mmTL, 934 g) that were injected intramuscularly 

 with 50 mg oxytetracycline (OTC) per kg body weight 

 on 3 November 1990 and 21 October 1989, respective- 

 ly. These fish were maintained at ambient light and 

 temperature in flow-through 1038-gallon seawater 

 tanks located at the Keys Marine Laboratory in the 



Florida Keys. The smaller specimen survived 11 

 months after OTC treatment; the larger fish was 

 sacrificed after 22 months. 



Nonlinear regression of all available age and length 

 data (using FSAS; Saila et al. 1988) was used to esti- 

 mate parameters of the von Bertalanffy growth 

 equation, 



It = L^(l-e(-K<t-t„))), 



where If is total length (mm), t is age (years), L^ is 

 asymptotic length, K is the Brody growth coefficient, 

 and to is the age at zero length (von Bertalanffy 1957). 

 Likelihood ratio tests were used to compare male and 

 female von Bertalanffy parameter estimates (Kimura 

 1980, Cerrato 1990). Nonlinear regression was used to 

 fit the exponential equation, WW or GW = aTL'', to 

 whole- or gutted-weight and total-length data. 



Histological preparations of gonads were made to 

 determine gonad developmental class, following the 

 criteria presented by Moe (1969) for red grouper Epi- 

 nephelus morio. Initially, gonad samples were em- 

 bedded in paraffin, but beginning with fish sampled in 

 1988, gonads were embedded in plastic (glycol meth- 

 acrylate) because of its superior tissue-infiltrating 

 abilities. Gonad samples were sectioned to a thickness 

 of 3.5f.im and stained with Weigert's hematoxylin and 

 eosin Y for microscopic examination. Spawning was in- 

 ferred from seasonal changes in the relative abundance 

 of fish having ovaries containing vitellogenic oocytes 

 or testes containing sperm in their efferent ducts. Sizes 

 or ages at maturity were determined from changes in 

 the proportion of mature fish over the entire age range 

 or across 50 mm size-classes. 



Results 



Age and growth 



Opaque bands can be recognized and counted on thin- 

 sectioned jewfish sagittae. Initial counts of opaque 

 bands by two independent readers agreed on 62% 

 (237/384 fish) of sections analyzed, with 91% (348/384) 

 of all counts either in agreement or differing by one. 

 After a second, joint reading, agreement was reached 

 on opaque-band counts for all but two sections, leav- 

 ing 382 specimens for analysis of age and growrth. 



The annual pattern of monthly mean marginal incre- 

 ment ratios and observations from two OTC-marked 

 jewfish support the hypothesis that annuli form once 

 each year. Mean marginal increment ratios were 

 greater than 70% during November- April and declined 

 to a minimum of 20% in June. The mean marginal in- 

 crement ratio remained less than 30% through August 

 (Fig. 1). For a large number of specimens captured 



