18 
Fishery Bulletin 99(1 ) 
Table 1 
Numbers of cobia examined histologically from each sampling area. 
Area 
Males 
n 
Months of capture 
Females 
n 
Months of capture 
Southeastern United States (SEUS) 
33 
February-May 
60 
February-June 
Eastern Gulf of Mexico (EGOM) 
43 
February-December 
60 
March-December 
North-central Gulf of Mexico (NCGOM) 
48 
March-October 
204 
February-September 
Western Gulf of Mexico (WGOM) 
23 
May-August 
59 
May-August 
Totals 
147 
383 
Results 
Fish collections 
A total of 530 cobia (147 males, 383 females) from 
the southern United States were collected for histo- 
logical analysis. The months and numbers of sam- 
ples collected varied by region, but in all regions 
fish were collected primarily during the reproduc- 
tive season (Table 1). Specimens ranged from 35.5 
to 138.5 cm FL for females and 36.5 to 127.0 cm FL 
for males. Weights ranged from 0.64 to 34.93 kg for 
females and 0.91 to 40.82 kg for males. 
Accurate estimates of the size and age at sexual ma- 
turity of cobia from the southern United States could 
not be determined in this study. Small, immature spec- 
imens were rare in recreational catches owing to a 
minimum retention size of 84 cm FL for cobia in state 
territorial waters and the EEZ. We collected only six 
sexually immature specimens (all females from the 
EGOM ) during this study. The smallest reproductively 
active female encountered was 70 cm FL. 
Spawning season and gonadal development 
Cobia have a protracted spawning season (April 
through September) throughout the southern United 
States as determined from GSI values and histo- 
logical assessments. There was no significant differ- 
ence (P>0.05) in GSI values between corresponding 
months in 1996 and 1997 for either males or females 
in any region, with the exception of males in Septem- 
ber from the NCGOM (P=0.049). Therefore, monthly 
data for 1996 and 1997 by region were combined 
(Fig. 2). GSI values for both sexes in SEUS increased 
sharply from April to May (Fig. 2A), indicating the 
onset of the reproductive season. GSI values for 
both sexes of cobia from EGOM began to increase 
in March, peaked in July, and declined and leveled 
off thereafter (Fig. 2B). GSI values for females from 
NCGOM increased in March, peaked in May, and 
then declined through September (Fig. 2C). In contrast, 
GSI values of males from NCGOM steadily increased 
through July, then fell precipitously in August (Fig. 20. 
GSI values for males reached similar mean maxima in 
8 
7 
6 
5 
4 
3 
2 
1 
A A Female 
■ Male 
f A 
' // 
■ 
■: . 
t ; 
7 
6 
B 
5 
'•3' 
ISS 
3 
▲ 
2 
A t 
1 
■ 
A * ■ ■ i - A A 
. ' • ■ 
6 
5 
c 
4 
▲ 
* i 
3 
A 
A • 
A 
2 
1 
* A 
‘ , • 
■ 
J FMAMJ JASOND 
Month 
Figure 2 
Monthly (1996 and 1997 combined) gonadosomatic index (GSI) 
values for cobia from the southern United States. Values rep- 
resent mean ±1SE. (solid triangles=female, solid squares=male) 
(A) Southeastern United States. (B) Eastern Gulf of Mexico. (C) 
North-central Gulf of Mexico. 
the SEUS and the NCGOM regions but were lower in 
the EGOM. However, mean GSI values of females were 
higher in both May and June for cobia from the SEUS 
than during any month from the Gulf of Mexico (Fig. 2). 
