KEIRANS ET AL.: DIFFERENTIATION OF PRIONOTUS EGGS 



confirmed. The data also show that in 1973 and 1974, 

 the ratios of eggs collected in plankton samples and 

 identified based upon morphology and immuno- 

 chemical reactions for nothern and striped searobins 

 were 1.1:1 and 1.6:1, respectively. These ratios are 

 similar in magnitude to the ratio of northern and 

 striped searobin adults observed by Marshall (1946). 

 Finally, the data indicate that egg diameter and oil 

 globule distribution cannot serve to reliably dis- 

 tinguish northern from striped searobin eggs. An 

 immunochemical distinction can be made that sug- 

 gests morphology alone is inadequate to provide a 

 positive identification of P. evolans eggs. 



The course of future research in immunochemical 

 taxonomy of fish eggs should emphasize an increase 

 in sensitivity, as well as automation of the analysis. 

 At present, the utility of the immunodiffusion 

 method is limited by its labor-intensive nature. Ini- 

 tial stages of the analysis require manual sorting of 

 ova from plankton samples that is tedious, time- 

 consuming, and subject to error. Bowen et al. (1972) 

 initiated studies in which a moderate degree of suc- 

 cess was achieved in sorting fish ova from pelagic 

 plankton samples on sucrose density gradients. 

 However, estuarine plankton samples that contained 

 a wide range of particulate materials characterized 

 by different sizes, densities, and shapes, and that also 

 included high levels of detrital materials, disturbed 

 the gradients sufficiently to destroy separation 

 potential. Despite the recognized limitations, there 

 is currently no practical alternative to manual sort- 

 ing of plankton samples. 



Immunodiffusion analysis requires that individual 

 fish eggs be subjected to several manual manipula- 

 tions, with the final determination in solid media re- 

 quiring the careful applications of reagents. Screen- 

 ing large numbers of planktonic ova with several dif- 

 ferent antisera becomes impractical on a large scale. 

 A more rapid and potentially more specific approach 

 to immunochemical ichthyoplankton identifications 

 might employ monoclonal antibodies coupled to 

 fluorescent indicator molecules. The antibody prod- 

 ucts of fused mouse lymphocytes and myeloma cells 

 may be screened and selected for exquisite specificity 

 to single antigenic determinants or epitopes using 

 egg antigens of known origin, preferably those 

 associated with the chorion surface, to procure a 

 reagent that would specifically label ova without re- 

 quiring that each egg be mechanically ruptured. 

 Identifications might be based upon the differential 

 fluorescence characteristic of a particular fluo- 

 rescent label associated with a selected antibody and 

 labelled eggs might be isolated using a fluorescence- 

 activated cell sorter. 



The utility of immunochemical identifications with 

 demonstrably superior accuracy to conventional 

 methods has been established with both intergeneric 

 and interspecific differentiations. Several systems 

 remain which might benefit from immunochemical 

 differentiations, such as the complete elucidation of 

 several sciaenid and clupeid species which occur in 

 complex estuarine systems, such as the Chesapeake 

 Bay and Potomac River estuary. Relationships be- 

 tween scombrids, bothids, and pleuronectids with 

 more southerly distributions would serve to delineate 

 adult ratios, population distributions, and spawning 

 seasons. Finally, the capability of the immune system 

 to differentiate among epitopes with relatively small 

 structural difference (Karush 1962) might eventually 

 be applied to the detection of racial differences or 

 subpopulation distinctions among fish ova of the 

 same species. 



ACKNOWLEDGMENTS 



The Noyes Foundation provided fellowship funds 

 for the senior author. Michael Criss and Marian 

 Glaspey assisted in collecting the samples. 



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BlGELOW, H. B., AND W. C. SCHROEDER. 



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67 



