INSTANTANEOUS REPRODUCTIVE EFFORT IN FEMALE AMERICAN OYSTERS, CRASSOSTREA-VIRGINICA, MEASURED BY A NEW IMMUNOPRECIPITATION ASSAY

An immunoprecipitation assay was developed for measuring instantaneous reproductive effort in female American oysters, Crassostrea virginica . Oysters were injected with C-14-leucine and incubated in situ for 1 to 30 h periodically throughout the annual gametogenic cycle. Gonadal protein labeled with C-14-leucine was precipitated from an oyster homo genate with rabbit anti-oyster egg IgG as the primary antibody. Antibo dy-oyster egg protein complex was further purified by immunoadsorption with staphylococcal protein A cell suspension. The quantity of oyster eggs was determined by single-ring immunodiffusion. A mathematical mo del was developed to calculate the instantaneous reproductive rate of oysters and to estimate the number of days required from the initiatio n of gonadal development to spawning. The oyster population was lightl y to moderately infected with a protozoan parasite, Perkinsus marinus. A negative correlation between the intensity of infection and the rat e of gonadal production suggests that P. marinus retards the rate of g amete development. The seasonal cycle of gamete production determined by direct measurements of egg protein production was not equivalent to that determined by standard gonadal-somatic index (GSI), except at th e most basic level. GSI was highest during the spring spawning peak, b ut the rate of gamete production was highest in the fall. Accordingly, the two measurements, rate versus standing crop (volume of gonad), re veal a substantially different picture about the details of the spawni ng season. Estimates of the time required to reach spawning condition ranged from several weeks to 1 or 2 months; these values agree with pu blished estimates derived from less direct methods. Direct rate measur ements thus seem to accurately reflect the true rate at which gametic tissue is produced in the field. A positive correlation between oyster size and the estimated days to spawn suggests that larger oysters req uire longer to prepare to spawn. Furthermore, the range in observed so matic and gametic growth emphasizes the conservatism of somatic growth and the volatility of gonadal growth that is borne out by the results of population dynamics models of oysters.