Brown-Peterson et at: Reproductive biology of Rcichycentron canadum 
21 
FOM ranged from 11% in the WGOM to 
59% in the EGOM. On average, 19% of the 
females from SEUS and NCGOM were un- 
dergoing FOM. 
The presence of POFs in cobia ovaries in- 
dicated spawning had commenced, although 
POFs were uncommonly observed; the great- 
est density of POF recorded was five per lOOx 
microscopic field of view. Postovulatory folli- 
cles occurred in cobia ovaries in the late-de- 
veloping class from all regions during April 
through September, suggesting that although 
cobia were in the late-developing class by 
March, spawning commenced in April. The 0- 
tol2-h POF stage (Fig. 5A) was infrequently 
observed (16%) and was absent in females 
from the WGOM. The 24-h POF stage (Fig. 
5B) was the most frequently observed (51%) 
and was most common in cobia from EGOM 
and NCGOM. The 48-h POF stage (33%, Fig. 
5C) was difficult to distinguish from gamma- 
and delta-stage atresia, and most commonly 
occurred in cobia from theWGOM. 
Spawning frequency 
Estimates of monthly spawning frequency 
for the POF and FOM methods (Table 6) 
were consistent throughout the spawning 
season in all regions. Both methods showed 
good agreement for fish from SEUS and 
NCGOM. The POF method indicated a more 
frequent estimate of spawning rate in the 
NCGOM. On the other hand, the FOM 
method resulted in a more frequent spawn- 
ing rate for cobia from the WGOM. Cobia 
from SEUS and NCGOM were estimated to 
spawn every 4 to 5 days, whereas those from 
WGOM spawned every 9 to 12 days. Chi- 
square analysis showed no significant differ- 
ence in spawning frequency estimates for the 
three regions for either the POF (P=0.08) or 
the FOM (P=0.409) method. Months where 
fewer than five specimens had late develop- 
ing ovaries were eliminated from the anal- 
ysis because spawning frequency estimates 
would probably be inaccurate. No estimate 
was made for cobia from the EGOM, and 
spawning frequencies for the WGOM were 
based on fish captured in July. Spawning 
frequency estimates for SEUS were based 
on data from April, May, and June, whereas 
estimates for NCGOM were based on data 
from April, May, and July. 
Relationship of ovary weight and 
volume 
Direct volume measurements were per- 
formed for 86 females with ovarian weights 
Figure 3 
Stages of atresia in cobia ovaries. (A) Alpha (a), beta (j3), and gamma (y) 
stage atresia in a late-developing or spent ovary. Scale bar = 0.1 mm. 
(B) Alpha-stage atresia of a hydrated oocyte (0). Scale bar = 0.1 mm. 
(C) Beta ( /3), gamma (y) and delta (<5) stages of atresia in a spent ovary. 
Scale bar = 0.1 mm. 
