Abstract. — Restriction-fragment 

 length polymorphism (RFLP) 

 analysis of mitochondrial mtDNA 

 was used to identify morphologi- 

 cally similar eggs of spring spawn- 

 ing sciaenids in lower Chesapeake 

 Bay. During spring 1990 and 1991, 

 ichthyoplankton surveys were con- 

 ducted in lower Chesapeake Bay 

 to estimate seasonal egg produc- 

 tion and population biomass of 

 black drum, Pogonias cromis. 

 Rearing experiments indicated 

 that at least three species of 

 sciaenid (silver perch, Bairdiella 

 chrysoura; weakfish, Cynoscion 

 regalis and P. cromis) were spawn- 

 ing in the survey area during both 

 years. Specific identification of 

 eggs based on previously pub- 

 lished ranges of outside egg diam- 

 eter (OED) were not reliable be- 

 cause of considerable overlap in di- 

 ameter distributions. However, 

 analysis of weekly OED frequen- 

 cies revealed the presence of three 

 modes which differed in temporal 

 occurrence, suggesting the prod- 

 ucts of three species. Genetic typ- 

 ing of eggs using RFLP analysis of 

 mtDNA confirmed the presence of 

 three species, but demonstrated 

 that eggs of certain size classes 

 represented two species. These 

 results illustrate that reliance on 

 previously published ranges of egg 

 diameter for specific identification 

 of spring-spawning sciaenids may 

 overestimate the spawning bio- 

 mass of black drum in Chesapeake 

 Bay by as much as 50% owing to 

 misidentification of weakfish eggs. 



Morphometric and genetic 

 identification of eggs of 

 spring-spawning sciaenids in 

 lower Chesapeake Bay* 



Louis B. Daniel III 



John E. Graves** 



School of Marine Science 

 Virginia Institute of Marine Science 

 The College of William and Mary 

 Gloucester Point, Virginia 23062 



At least five species of the family 

 Sciaenidae (silver perch, Bairdiella 

 chrysoura; spotted seatrout, 

 Cynoscion nebulosus; weakfish, C. 

 regalis; northern kingfish, Menti- 

 cirrhus saxatilis; and black drum, 

 Pogonias cromis) are purported to 

 spawn during the spring in lower 

 Chesapeake Bay (Joseph et al., 

 1964; Lippson and Moran, 1974; 

 Johnson, 1978; Brown, 1981; Olney, 

 1983; Cowan et al., 1992). The eggs 

 of spring-spawning sciaenids in 

 lower Chesapeake Bay are morpho- 

 logically similar, ranging in outside 

 egg diameter (OED) from 0.66 to 

 1.18 mm, and having single or 

 multiple oil globules of varying 

 sizes (Johnson, 1978; Olney, 1983). 

 As a result, specific identification of 

 eggs based on morphological crite- 

 ria is problematic. Holt et al. ( 1988) 

 suggested that it may not be pos- 

 sible to determine the specific iden- 

 tity of sciaenid eggs from morpho- 

 logical criteria; Joseph et al. (1964) 

 reported that positive identification 

 could only be achieved with supple- 

 mental hatching studies. 



Hatching studies have tradition- 

 ally been used to identify morpho- 

 logically similar eggs, including 

 those of sciaenids. Joseph et al. 

 (1964) cultured eggs of several sci- 

 aenids collected at a single station 



in southern Chesapeake Bay (16 

 May 1962) and raised larvae to an 

 identifiable size (5-7 mm). The 

 smallest eggs (0.630-0.777 mm) 

 were found to be B. chrysoura, 

 whereas the larger eggs (0.814- 

 1.110 mm) developed into P. cromis. 

 Culture of eggs (0.777-0.950 mm) 

 collected during early June pro- 

 duced no P. cromis but did result in 

 larvae of B. chrysoura and C. 

 regalis. In contrast, Olney (1983) 

 suggested that eggs of P. cromis, C. 

 regalis, B. chrysoura, and Ment- 

 icirrhus spp. were included in a 

 size-frequency distribution of mor- 

 phologically similar eggs collected 

 from May through August in lower 

 Chesapeake Bay, but that identifi- 

 cations based on diameter were 

 ambiguous because of the high de- 

 gree of overlap in diameter distri- 

 butions (Table 1). Confounding this 

 problem is the observation that egg 

 size may change with varying sa- 

 linity or as the spawning season 

 progresses (Johnson, 1978). 



Because many species of Sci- 

 aenidae in lower Chesapeake Bay 

 spawn concurrently and have mor- 

 phologically similar eggs, most 

 studies have relied either on previ- 

 ously published egg size distribu- 

 tions or rearing for identification 

 (Holt et al., 1985, 1988; Comyns et 



Manuscript accepted 10 November 1993 

 Fishery Bulletin 92:254-261 (1994) 



"Contribution No. 1818 of the Virginia Institute of Marine Science. 

 **To whom reprint requests and correspondence should be sent. 



254 



