400 
Fishery Bulletin 1 10(4) 
Table 1 
Stage of ovarian development was determined for female cobia (Rachycentron canadum) collected during the period from April to 
June in both 2007 and 2008 for this study of inshore spawning of cobia in South Carolina. Phases were based on descriptions of 
teleost oocyte development by Wallace and Selman (1981) and modified from Roumillat and Brouwer (2004) and Brown-Peterson 
et al. (2011). FOM=final oocyte maturation; POF=postovulatory follicle. 
Phase 
Subphase 
Description 
Immature 
Only oogonia and primary oocytes present. Fish has not yet reached 
sexual maturity and is incapable of spawning. 
Developing 
Primary growth oocytes dominate. A few early vitellogenic oocytes 
may be present and are <500 pm in diameter. Cortical alveoli 
visible. On the basis of diameter, there is a dominant batch of small 
vitellogenic oocytes and a few larger vitellogenic oocytes. Fish has 
not yet spawned this season. 
Spawning capable 
Late developing 
Primary growth, cortical alveolar, early vitellogenic and advanced 
vitellogenic oocytes present, with the diameter of oocytes in the 
largest batch at 500-850 pm. On the basis of diameter, there are 
at least 2 distinct batches of vitellogenic oocytes. Some atresia may 
be present. Fish is capable of spawning and may have previously 
spawned. 
Actively spawning 
One batch of oocytes undergoing FOM (through hydration), as 
evidenced by lipid coalescence and a diameter >850 pm. More 
advanced stages of FOM also will show migration of nucleus to 
animal pole. Oocytes in the next-largest batch are 300-500 pm in 
diameter. Spawning imminent. 
Past spawner 1 — recent spawning 
Recent POFs are abundant and distinguished by size (>250 pm 
across longest axis) and morphological features. Recent POFs 
are amorphous and clearly show multiple infoldings of thecal and 
granulose cells Oocytes in the largest batch are 300-550 pm in 
diameter. Fish has spawned within 0-24 hr. 
Past spawner 2 — previous spawning 
Degradation of POFs indicates spawn was >24 hr prior. Older POFs 
are triangular in shape, condensed, and less numerous compared 
with recent counterparts. Oocytes in the largest batch are 550- 
700 pm in diameter. 
Regressing 
Majority of largest batch of vitellogenic oocytes undergoing atresia. 
Oogonia and primary growth oocytes may be present. This stage is 
indicative of cessation of spawning for the season. 
Regenerating 
Oogonia and primary growth oocytes dominate. Other oocytes are 
in late stages of atresia. 
ing the questionable slides. Percent composition (PC) of 
females in each of the ovarian maturation phases was 
calculated separately for females collected inshore and 
for females collected offshore: 
p c = { n / r ) x100 ’ 
where n s = the number of female samples in phase s; and 
T = the total number of samples. 
Egg-development study 
Identification and aging of candidate eggs from the 
plankton collections were accomplished by using a time- 
series reference collection of cobia eggs obtained from 
wild-caught adult cobia spawned in the laboratory in 
2007 and 2008 for the egg-development study described 
below. Cobia yolksac larvae from the egg-development 
study in 2007 served as reference for the identifica- 
tion of young larvae in the plankton collections. The 
temperature treatments during the egg-development 
study of hatchery-reared eggs fell within the measured 
range of surface temperatures (20.1-30.0°C) encountered 
in PRS and SHS during May and June of both years 
(2007-2008). 
In 2007 at the Hollings Marine Laboratory in 
Charleston, South Carolina, 4 fiberglass hatching cones 
(170 L) were equipped with aerators and heaters and 
filled with seawater (34.5 psu) from Charleston Harbor 
that had been filtered (5 pm) and UV-sanitized after 
settling for 3 days. The water in these cones was heated 
to 22.5°C, 25.0°C, 26.5°C, and 29.0°C, respectively, and 
