lefebvre and Denson: Inshore spawning of Rachycentron canadum in South Carolina 
399 
Figure 1 
Coastal South Carolina and estuaries that cobia (Rachycentron canadum) enter during 
their annual northward spring migration. For this study of inshore spawning, cobia 
were collected from 2 inshore estuaries. Port Royal Sound and St. Helena Sound, 
and offshore in 2007 and 2008. Triangles indicate stations sampled in each estuary 
during the ichthyoplankton survey conducted in 2008. Map by Jessica Boyton (South 
Carolina Department of Natural Resources). 
0SI= ( GW /sw ) x 10 °- 
where GW = gonad weight (grams); and 
SW = somatic weight (grams). 
To determine whether GSI values for male and female 
cobia were significantly different, a Wilcoxon rank test 
was performed. To evaluate if ovarian maturation dif- 
fered between inshore and offshore collections of female 
cobia, a Wilcoxon rank test was performed with the 
GSI as a proxy for maturation for statistical purposes. 
Nonparametric Wilcoxon tests were performed because 
the data displayed non-normality, which resulted from 
the capture of 2 actively spawning females. A Atest was 
used to determine if differences in GSI between inshore 
and offshore females persisted after exclusion of the GSI 
values from the 2 actively spawning females. 
Histological analyses were limited to samples col- 
lected from female cobia because males are capable 
of spawning year-round (Brown-Peterson et al., 2001). 
Homogenous ovarian development has been documented 
previously for cobia (Lotz et al., 1996; van der Velde et 
al., 2010); therefore, a single portion of tissue (-50-100 
mg) from the middle of one ovarian lobe was fixed in 
10% neutral buffered formalin before being rinsed in 
freshwater and stored in 50% isopropyl alcohol at least 
24 hr before processing. Tissue samples were dehy- 
drated, infiltrated and blocked in paraffin, sectioned to 
6 pm with a rotary microtome, mounted on glass slides, 
and stained with hematoxylin and eosin-y according 
to standard histological techniques (Humason, 1972). 
Slides were examined under a compound microscope 
at lOOx magnification and staged according to ovarian 
development. Ovarian phases (Table 1) were determined 
on the basis of descriptions of teleost oocyte develop- 
ment in Wallace and Selman (1981), with modifications 
from Roumillat and Brouwer (2004) and Brown-Peter- 
son et al. (2011). When present, postovulatory follicles 
(POFs) were categorized as either less than or equal to 
or greater than 12 hr old, on the basis of rates of POF 
atresia found in spotted seatrout ( Cynoscion nebulosus 
[Roumillat and Brouwer, 2004]). Vitellogenic oocytes 
of specimens that had been frozen or had begun to de- 
cay before collection superficially resembled oocytes at 
the beginning stages of FOM, with nucleus migration 
and early lipid coalescence. To avoid confusion between 
FOM and damaged tissue, FOM stages earlier than the 
hydration stage were not addressed. All samples were 
staged by a second, independent reader. All discrepan- 
cies were resolved by both readers simultaneous view- 
