20 
Fishery Bulletin 99(1) 
Table 4 
Percentage of cobia in each ovarian maturity class for NCGOM (Destin, FL, to Chandelier Islands, LA). Monthly data from 1996 
and 1997 were combined. Percentage atresia was calculated for each developmental stage for ovaries with alpha- or beta-stage 
atresia only. 
Month of capture 
Class 
February 
0=10) 
March 
0 = 6) 
April 
(rc=20) 
May 
0=112) 
June 
0=1) 
July 
0=25) 
August 
0=8) 
September 
0=22) 
Early developing 
60 
0 
0 
4.5 
0 
0 
0 
0 
% atresia 
60 
— 
— 
20 
— 
— 
— 
— 
Mid developing 
0 
33 
10 
7 
0 
4 
0 
0 
% atresia 
— 
100 
100 
62 
— 
0 
— 
— 
Late developing 
0 
67 
90 
88.5 
100 
64 
37.5 
18 
% atresia 
— 
75 
44 
38 
0 
31 
33 
25 
Spent 
10 
0 
0 
0 
0 
28 
50 
23 
% atresia 
too 
— 
— 
— 
— 
86 
100 
80 
Regressed 
30 
0 
0 
0 
0 
4 
12.5 
59 
% atresia 
0 
— 
— 
— 
— 
0 
0 
100 
Table 5 
Percentage of cobia in each ovarian maturity class for 
WGOM (Port Aransas, TX) in 1996. Percentage atresia was 
calculated for each developmental stage for ovaries with 
alpha- or beta-stage atresia only. 
Class 
Month of capture 
May 
0=1) 
June 
0=8) 
July 
0=48) 
August 
0=2) 
Mid developing 
0 
0 
4 
50 
% atresia 
— 
— 
50 
0 
Late developing 
100 
100 
73 
50 
% atresia 
0 
0 
5.7 
0 
Spent 
0 
0 
21 
0 
% atresia 
— 
— 
100 
— 
Regressed 
0 
0 
2 
0 
% atresia 
— 
— 
100 
— 
SEUS and the NCGOM, and females in the late develop- 
ing class occurred in both areas by March (Tables 2 and 4). 
Spent females were initially observed in July in the Gulf 
of Mexico (Tables 3-5), although some females remained 
in the late developing class through September (Tables 3 
and 4). Some females in the regressed class occurred in 
July throughout the Gulf of Mexico (Tables 3-5). In July, 
lengths of spent and regressed fish ranged from 88.0 to 
93.0 cm FL in the EGOM, from 85.5 to 102.1 cm FL in the 
NCGOM, and from 86.4 to 128.3 cm FL in the WGOM. 
Ovarian tissue in all classes of maturity showed atre- 
sia throughout the reproductive season. Alpha- and beta- 
stage atresia of yolked oocytes (Fig. 3A) was most preva- 
lent in spent fish, but also occurred in females in the early, 
mid and late developing ovarian classes (Tables 2-5). Atre- 
sia of hydrated oocytes (Fig. 3B) occurred in ovaries in the 
late developing and spent classes only (5-10%). Atresia of 
nonyolked oocytes was difficult to recognize but was com- 
mon (50-90%) in early developing ovaries. The later stag- 
es of atresia (gamma and delta, Fig. 30 occurred in ova- 
ries in all maturity classes. Many late developing females 
(60-85%) from the SEUS exhibited alpha- or beta-stage 
atresia during March through May (Table 2). Similarly, fe- 
males from NCGOM exhibited high levels of atresia (75%) 
in ovaries in the late developing class during March (Table 
4). Less atresia (38-50%) occurred during April and May 
in the ovaries of cobia from the Gulf of Mexico (Tables 3 
and 4) as compared with cobia from the SEUS (Table 2). 
Female cobia underwent final oocyte maturation (FOM) 
in all four areas sampled during April through September. 
The early stages of FOM were characterized by early lip- 
id coalescence (Fig. 4A), followed by complete lipid coales- 
cence and migration of the nucleus to the periphery of the 
oocyte (Fig. 4B). The final stages of FOM, characterized 
by breakdown of the nuclear membrane, yolk coalescence 
and hydration, were not observed in any sample. Final oo- 
cyte maturation was a synchronous process and most oo- 
cytes within an ovary were in the same stage of FOM 
(Fig. 4C). The percentage of mature oocytes (>600 pm) 
undergoing FOM varied from 5% to 84% of the oocytes 
within a lOOx microscopic field of view for all ovaries ex- 
amined. Females from the EGOM had the highest mean 
percentage of mature oocytes undergoing FOM (49%). The 
mean percentage of mature oocytes undergoing FOM was 
lower, but similar, among the other regions (NCGOM, 
19%; SEUS, 16%; WGOM, 15%). The mean percentage of 
females in the late-developing ovarian class undergoing 
