248 



Fishery Bulletin 91(2), 1993 



and female GSI reached the observed minimum value 

 of0.84byJuly(Fig. 2). 



Spawning frequency 



In order to estimate proximity to time of spawning 

 and designate females as day-0 and day-1 spawners 

 for spawning frequency calculation (Table 2), we con- 

 structed a time-scale of coalescence-stage oocytes, hy- 

 drated oocytes, and postovulatory follicles based on 

 literature reports and our observations (Fig. 3). From 

 previous work on related sciaenids, it is known 

 that lipid coalescence, germinal vesicle migration, 

 and yolk coalescence occur beginning in morning 

 samples with hydration becoming evident as the 

 day progresses (DeMartini & Fountain 1981, 

 Fitzhugh et al. 1988, Brown-Peterson et al. 1988). 

 Although exact capture times for some black 

 drum were not known, females exhibiting germi- 

 nal vesicle migration and yolk coalescence were 

 commonly taken in haul-seine and gillnet sets 

 which were typically landed during morning 

 hours. 



A follicle, comprised of an inner layer of epi- 

 thelial granulosa cells and an outer layer of the- 

 cal cells, surrounds each hydrated oocyte. Fol- 

 lowing ovulation, POFs were present as the 

 evacuated follicle remaining in the ovary. Recent 

 POFs were denoted by linear arrangement of the 

 granulosa cell layer and apical location of very 

 prominent nuclei. These cellular arrangements 



imparted the appearance of a well-defined lu- 

 men and convoluted shape to the POF and 

 were observed from ovaries sampled between 

 2400 and 0300 h from preliminary samples 

 taken by hook-and-line in March 1986. We con- 

 cluded that spawning occurred earlier that 

 same night, and used these March 1986 

 samples as an example of recent POFs. Three 

 females sampled from trawl landings in 1987 

 with recent POFs also had fully-hydrated eggs 

 in the lumen of their ovaries, indicating active 

 spawning and coinciding with reports of onset 

 of spawning after dusk (Mok & Gilmore 1983, 

 Holt et al. 1985). From interviews of commer- 

 cial fishermen, capture of black drum in trawls 

 often occurred after dusk and throughout the 

 night, with fish being placed into ice as they 

 were captured. We routinely sampled black 

 drum the morning following their capture, and 

 therefore it is likely that the recent POFs we 

 observed are from fish captured up to 8 h after 

 spawning (Fig. 3). 



Over the 1986-87 spawning season, we 

 sampled limited numbers of females bearing 

 POFs (50 females taken from 8 different samples) in- 

 dicating that duration of POFs may be brief. Hydra- 

 tion-stage oocytes, occurring together with visibly- 

 degenerated POFs, were evident in only 19 females. 

 Additionally, only 1 female contained recent POFs as 

 well as degenerating POFs. Older degenerating POFs 

 were similar in appearance to 24h-old follicles illus- 

 trated in Hunter et al. (1986) from skipjack tuna 

 Katsuwonus pelamis spawning at 23-24°C. Therefore, 

 POF duration may be limited to 24-48 h following ovu- 

 lation (Fig. 3). 



Coalescence 



I 



Hydration 



Ovulation and Spawning 



□ 



Day 



-12 -10 -8-6-4-2 2 4 6 



Hours from onset of spawning 



Day 1 8 10 12 14 16 18 20 22 24 26 28 30 



Day 2 32 34 36 



I — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — | — i — i — i 



0000 0400 0800 1200 1600 2000 

 Time of Day 



Figure 3 



Generalized time-scale of final oocyte maturation and spawning of 

 black drum Pogonias cromis, determined from observations and lit- 

 erature reports (see text). 



