Daniel and Graves: Morphometry and genetic identification of sciaenid eggs 



257 



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OUTSIDE EGG DIAMETER (mm) 



Figure 1 



Frequency distributions of outside egg diameters of sciaenid eggs collected 

 over six weeks during spring 1990 in lower Chesapeake Bay. 



mm and larger (n=32), all pos- 

 sessed the restriction fragment 

 pattern diagnostic for P. cromis. 



Discussion 



A total of 62 eggs, representing all sciaenid egg 

 size classes collected in lower Chesapeake Bay, was 

 identified with diagnostic Hi n dill restriction frag- 

 ment patterns. Bairdiella chrysoura, C. regalis, and 

 P. cromis were the only species of sciaenids identi- 

 fied; no other restriction fragment patterns were 

 observed. Genetic identification of eggs designated 

 Type A (<0.850 mm, n=12) resulted in 11 individu- 

 als of B. chrysoura and one specimen (0.825-mm 

 OED size class) of C. regalis (Fig. 3). Cynoscion 

 regalis composed the majority of type-B eggs (0.850- 

 0.975 mm, rc = 18) analyzed, but seven of the 10 larg- 

 est type-B eggs (0.975-mm OED size class) were 

 identified as black drum. Type-C eggs, those 1.00 



Identifications of eggs of sci- 

 aenids are often based on pub- 

 lished diameter distributions or 

 hatching experiments, or both. 

 Results of hatching experiments 

 and genetic analysis in this 

 study indicate that samples of 

 eggs of a single size class may 

 represent the products of two or 

 more species. For example, eggs 

 designated Type I (<0.80 mm) 

 and identified as silver perch by 

 Joseph et al. (1964) were shown 

 with genetic analysis to contain 

 eggs of both weakfish and silver 

 perch. Similarly, eggs designated 

 Type II (>0.85 mm) and identi- 

 fied as black drum by Joseph et 

 al. (1964) were shown with rear- 

 ing and genetic analysis to con- 

 tain eggs of both weakfish and 

 black drum. 



During the present study, nei- 

 ther hatching experiments nor 

 genetic analysis identified eggs 

 as black drum that were smaller 

 than 0.975 mm OED. While tem- 

 porally limited, the results of 

 this study suggest that the 

 range in size for eggs of black 

 drum (0.975-1.125 mm) in lower 

 Chesapeake Bay may be more 

 restricted than those previously 

 reported. 

 The ranges of egg diameter overlapped for silver 

 perch and weakfish. Eggs genetically identified as 

 silver perch ranged in size from 0.650 to 0.825 mm, 

 in agreement with previously reported size ranges 

 for silver perch in the northwestern Gulf of Mexico 

 (0.59-0.82 mm, Holt et al., 1988) and Chesapeake 

 Bay (0.625-0.775 mm, Joseph et al., 1964). Although 

 Holt et al. (1988) identified eggs of silver perch as 

 small as 0.590 mm, no sciaenid eggs smaller than 

 0.650 mm OED were collected in the present study. 

 Sizes of eggs genetically identified as weakfish were 

 found to range from 0.825 to 0.975 mm in diameter. 

 These values are comparable with those reported by 

 Wisner ( 1965, 0.84-0.96 mm) but are narrower than 



