Barbieri et al.: Maturity, spawning, and ovarian cycle of Micropogonias undulatus 



683 



1923) requires considerable subjective interpretation 

 given the extended spawning season of Atlantic 

 croaker, the generally asymptotic growth after age 

 2, and the great overlap in observed sizes at age 

 (Barbieri et al., 1994). Although Welsh and Breder 

 (1923) and Wallace ( 1940) have also used scales, prob- 

 lems in applying this method to Atlantic croaker have 

 been reported (Joseph, 1972). 



Sex ratios 



Our results on temporal fluctuations in Atlantic 

 croaker sex ratios agree well with previous reports 

 for the Chesapeake Bay and mid-Atlantic regions 

 (Welsh and Breder, 1923; Wallace, 1940). The pre- 

 dominance of females during the first 3-4 months of 

 spawning may indicate that either males start leav- 

 ing the estuary earlier than females as fish migrate 

 out of Chesapeake Bay or that spawning-phase fe- 

 males are more susceptible to the fishing gears used 

 in Chesapeake Bay (pound nets, haul seines, and gill 

 nets). During both years, the frequency of males de- 

 creased during the first two months of spawning and 

 began increasing again in October/November when 

 the first offshore trawl collections were obtained. 

 Mark-recapture studies are necessary to better evalu- 

 ate the migratory patterns of Atlantic croaker in 

 Chesapeake Bay and the mid-Atlantic region. 



Atresia of advanced yolked oocytes 



High levels of atresia typically have been used to 

 identify regressing ovaries, and for many teleosts, 

 have been described as representing a key histologi- 

 cal marker for the cessation of spawning (Hunter and 

 Macewicz, 1985, a and b; Hunter et al., 1986; 

 Dickerson et al., 1992). However, our results with 

 Atlantic croaker indicate that high levels of atresia 

 do not necessarily imply the end of spawning. Al- 

 though we found significant atresia of cortical alveoli 

 and partially yolked oocytes only in regressing ova- 

 ries, indicating it could in fact be used to mark the 

 end of spawning, major atresia of advanced yolked 

 oocytes was observed in actively spawning females 

 throughout the spawning season suggesting it may 

 represent a normal part of the reproductive biology 

 of Atlantic croaker. The fact that hydrated females — 

 either actively spawning or just about to spawn — 

 showed advanced yolked oocytes undergoing atresia 

 suggests that a portion of these oocytes are never 

 matured and spawned. In other words, it appears 

 that a surplus production of advanced yolked oocytes 

 is part of the reproductive strategy of Atlantic croaker. 

 Fully developed females may hydrate and spawn more 

 or less of these oocytes depending, for example, on en- 

 vironmental conditions. 



Evidence from laboratory studies seems to support 

 this hypothesis. Middaugh and Yoakum (1974) used 

 chorionic gonadotropin to induce laboratory spawn- 

 ing of Atlantic croaker. They found that although the 

 abdomen of females became extremely distended as 

 a result of oocyte hydration, only a limited number 

 of eggs could be stripped from each fish. More re- 

 cently, Trant and Thomas (1988) and Patino and 

 Thomas (1990) evaluated in vitro germinal vesicle 

 breakdown (GVBD, an index of final oocyte matura- 

 tion) in laboratory-spawned Atlantic croaker. They 

 reported that in this species there is always a re- 

 sidual number of "advanced oocytes" which fail to 

 complete GVBD or even enter the morphological 

 maturation process, suggesting that not all oocytes 

 in a spawning batch would be matured and spawned. 



Conclusion 



Because of the small number of gravid females col- 

 lected and the fact that POF's could be identified only 

 in running-ripe females, we were not able to esti- 

 mate batch fecundity and spawning frequency for 

 Atlantic croaker. However, our results have shown 

 that 1 ) Atlantic croaker mature at a smaller size and 

 earlier age than previously thought; 2) Atlantic 

 croaker are capable of spawning in the estuary, al- 

 though the magnitude of estuarine spawning is still 

 unclear; 3) they are multiple spawners with inde- 

 terminate fecundity, indicating that the only avail- 

 able estimates of fecundity (Morse, 1980) — those 

 based on the assumption of determinate fecundity — 

 should not be used for management; and 4) the oo- 

 cyte size-frequency method (MacGregor, 1957 ) should 

 not be used to estimate batch fecundity for this spe- 

 cies, because of the high levels of atresia of advanced 

 yolked oocytes observed in spawning females. Future 

 studies on the reproductive biology of Atlantic croaker 

 in Chesapeake Bay and the mid-Atlantic region 

 should concentrate on offshore, preferably fishery- 

 independent, trawl collections to obtain gravid fe- 

 males for batch fecundity estimates following the 

 hydrated oocyte method (Hunter et al., 1985). Rates 

 of deterioration and resorption of POF's must also 

 be evaluated in laboratory-spawned fish to determine 

 if the postovulatory follicle method (Hunter and 

 Macewicz, 1985a) can be used to estimate spawning 

 frequency for this species. 



Acknowledgments 



We would like to thank those Chesapeake Bay com- 

 mercial fishermen and James Owens (VIMS) who 



