Brown-Peterson et al.: Reproductive biology of Rachycentron canadum 
23 
determined with the FOM method, aver- 
aged 377,000 ±64,500 eggs and ranged from 
212,500 ±122,700 eggs in August (n= 5) to 
637,000 ±376,600 eggs in September (n-3) . 
Relative batch fecundity (Table 8) did not 
vary significantly from April through Sep- 
tember as determined by the NBF method 
(F=0.636, df=37, P=0.639) and the FOM 
method (F=0.468, df=24, P=0.759). Relative 
batch fecundity for the NBF method aver- 
aged 53.1 ±9.4 eggs/g ovary-free body weight 
throughout the reproductive season (77=39, 
Table 8) and it was lowest in August and 
highest in June. Relative fecundity values 
determined with the FOM method were low- 
er than those with the NBF method, averag- 
ing 29.1 ±4.8 eggs/g ovary-free weight ( 77 =25, 
Table 8), and were lowest in June and high- 
est in July. 
Potential annual fecundity for cobia was 
estimated from batch fecundity and spawn- 
ing frequency estimates. A female cobia 
weighing 20 kg from SEUS or NCGOM may 
potentially spawn 20,952,000 (FOM meth- 
od) to 38,232,000 (NBF method) eggs be- 
tween April and September. In contrast, the 
same size female from WGOM would po- 
tentially spawn 8,730,000 (FOM method) 
to 21,240,000 eggs (NBF method) between 
April and September, with the data provided 
here. 
Discussion 
Our data show that the reproductive biol- 
ogy of cobia is similar throughout the 
coastal waters of the southern United States. 
Although sample sizes from some regions 
and months were small due to reliance on 
recreational catches for samples, we feel the 
data adequately represent the reproductive 
population from the four regions. Spawning 
commences in April throughout the region, 
as evidenced by the presence of oocytes 
undergoing FOM as well as 24-h POFs. 
These findings are in agreement with pre- 
vious studies of cobia reproduction in the 
southeastern U.S. Atlantic Ocean (Smith, 
1995) and the north-central Gulf of Mexico 
(Biesiot et al., 1994; Lotz et al., 1996; Thomp- 
son et al. 2 ). Collections of larval cobia from 
the Gulf of Mexico during May through Sep- 
tember (Ditty and Shaw, 1992) also confirm 
the spawning season. Reproductive activity 
of female cobia probably ceases during Sep- 
tember in the Gulf of Mexico and extends 
at least through June in the SEUS. Smith 
(1995) reported that cobia from North Caro- 
lina spawned through July. Eggs and larvae 
Figure 5 
Postovulatory follicles (POF) in late-developing cobia ovaries. (A) 0- to 
12-h POF (arrows). Scale bar = 0.1 mm. (B) 24-h POF (arrows). Scale bar 
= 0.2 mm. (C) 48-h POF (arrow). Scale bar = 0.1 mm. 
