In Florida, culture of the sunray venus Macrocallista nimbosa is currently limited by seed supply. Hatcheries have not been able to condition and spawn brood stock on a predictable and consistent basis. The objective of this study was to determine the relative effects that temperature and diet have on the natural gametogenic cycle of this species so that improved conditioning protocols can be established for this species. The sunray venus M. nimbosa from west central Florida (Anna Maria Island) reached sexual maturity at a shell length >35 mm (age 6–8 mo). Small clams (mean shell length: 60 mm) had a 1:1 sex ratio, whereas larger clams (mean shell length: 129 mm) were predominantly female. This species exhibited a poorly defined annual reproductive cycle, and development was not synchronous between the sexes. Males developed mostly over the cooler months and spawned in the spring and early summer. Females exhibited two periods of relatively greater development: June to October and December to February, with relative little development occurring in November and from March to May. Nonetheless, mature individuals of both sexes were found throughout the year. All of these suggest that spawning within this population is almost continuous and that as females develop mature ova, they are released sporadically and fertilized by male clams, and a new generation of oocytes is rapidly produced. Given the large time over which gametes are produced, temperature does not seem to be critical. Instead, it is likely that M. nimbosa responds to fluctuations in food supply by rapidly developing gametes, spawning, and redeveloping. Future conditioning attempts should therefore focus on diet quality and quantity.
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Vol. 36 • No. 1