Cuellar et al.: Reproductive seasonality, maturation, fecundity, and spawning frequency of the vermilion snapper 



637 



and weights (g/total body weight and g/ovary-free 

 body weight [OFWT] ±1 g) . Ovaries were removed, 

 blotted dry, and weighed and fixed in 10% buffered 

 seawater formalin. After fixation, samples of ovarian 

 tissue were weighed with an Ohaus digital balance 

 (±0.001 g) for fecundity determination. Conversion 

 factors were developed for samples taken during the 

 first three months of the study because fresh gonad 

 weight and OFWT were not measured. When sam- 

 pling was not untertaken (September to April), ad- 

 ditional samples were purchased from the commer- 

 cial hook-and-line catch landed in Georgetown, South 

 Carolina. Commercial samples were used for histologi- 

 cal examination ( see below), both to define the spawn- 

 ing season and to gather atresia measurements. 



A modified gonadosomatic index (GSI) was used 

 to quantify the reproductive cycle. The GSI was calcu- 

 lated as GSI = {gonad weight/OFWT) x 100 (Nieland 

 and Wilson, 1993; Nikolsky, 1963). In order to make 

 comparisons with the findings of Grimes (1976), the 

 following gonad index (GI) equation was used: 



K G = (WT G I TL 3 ) x 10 6 , 



where WT - preserved weight of the gonad (g), and 

 TL = total length (mm). 



GI values from Grimes (1976) were compared with 

 GI values from the present study to evaluate pos- 

 sible differences between the two studies in repro- 

 ductive timing and size and age at maturity. 



A chi-square test was used to evaluate the sex ra- 

 tio of vermilion snapper. A 2 x 2 contingency table 

 was used to compare the sex ratios in Grimes ( 1976) 

 with those in the present study and to compare 

 MARMAP samples with commercial samples (Zar, 

 1984). Sex-ratio data were also analyzed by 50-mm 

 length classes by using a 2 x 4 contingency table (Zar, 

 1984) 



Histological analysis was used to assess maturity 

 and spawning activity and to verify whole-oocyte 

 staging. Gonad sections were prepared according to 

 the methods of Wenner et al. (1986). The develop- 

 mental stage of each ovary was identified by using 

 the criteria of Hunter et al. (1992) (Table 1). Each 

 ovary was also examined for the presence or absence 

 of the two stages of postovulatory follicles (POF's). 

 Testes were classified by means of the modified cri- 

 teria of Wyanski and Pashuk 2 (Table 2). 



Maturity definitions I-V from Hunter et al. ( 1992 1 

 were used to classify females. Mature females in- 



cluded the following: all active females; all inactive 

 mature females; inactive females with early yolked 

 oocytes and with alpha, beta, or no atresia; and in- 

 active females with unyolked oocytes and with al- 

 pha or beta atresia (Table 1). If testes were develop- 

 ing, ripe, spent, or resting, they were considered 

 mature (Table 2). 



Transverse sections of otoliths were made with a 

 Buehler Isomet low-speed saw. Sections were 

 mounted on slides, immersed in cedarwood oil, and 

 viewed under a dissecting microscope. The dissect- 

 ing microscope was linked by a video camera to a 

 MATROX frame grabber and personal computer with 

 OPTIMAS image analysis software. 



The following fecundity definitions from Hunter 

 et al. ( 1992) were used in the present study: 



Determinate fecundity Annual fecundity is fixed 



prior to the onset of the 

 spawning season. 



Indeterminate fecundity Annual fecundity is not 



fixed prior to the onset 

 of the spawning season, 

 and unyolked oocytes 

 continue to mature and 

 are spawned during the 

 spawning season. 

 Total number of eggs 

 spawned per year. 

 Standing stock of ad- 

 vance-stage yolked oo- 

 cytes (AYO's). 



Potential fecundity (PF) Total AYO's that mature 



per year. Potential fe- 

 cundity was considered 

 to be equivalent to the 

 standing stock of AYO's 

 in fully developed pre- 

 spawning females. 

 Total number of hy- 

 dra ted oocytes (HO's) re- 

 leased in one spawning. 



Annual fecundity (AF) 

 Total fecundity (TF) 



Batch fecundity (BF) 



2 Wyanski, D. M., and O. Pashuk. 1996. Processing and inter- 

 pretation of fish reproductive tissue at the Marine Resources 

 Research Institute of the South Carolina Department of Natu- 

 ral Resources. In preparation. 



If vermilion snapper is a determinate spawner, then 

 the following are expected: a hiatus will develop in the 

 frequency distribution of oocyte diameter between the 

 oocytes that mature for the season and the reservoir of 

 less advanced oocytes present year round; TF declines 

 over the spawning season; mean oocyte diameter 

 (MOD) increases over the spawning season; and the 

 spawning order of batches is consistent with the deter- 

 minate fecundity definition (see Hunter et al., 1992). 



To determine whether AYO's were randomly dis- 

 tributed throughout the ovary, the densities of AYO's 

 at six locations within the ovaries of nine fish were 



