The sunray venus (sunray) clam, Macrocallista nimbosa, is an alternative clam species reared in hard clam hatcheries in Florida. Current feeding practices follow those used for hard clam culture. This study aimed to identify whether a hard clam bi-algal Tisochrysis lutea and Chaetoceros neogracile diet was an optimal diet for post-set sunray clams or whether other microalgal dietary combinations could improve production. Six dietary bi-, tri-, or tetra-algal combinations consisting of four microalgae species (Tisochrysis lutea, Diacronema lutheri, Chaetoceros neogracile, and Thalassiosira weissflogii) were fed for 6 weeks; the growth, survival, and fatty acid profiles of post-set clams were evaluated. Clams fed equal proportions of T. lutea, D. lutheri, C. neogracile, and T. weissflogii had higher growth, while those fed equal proportions of T. lutea and C. neogracile had higher survival. The poorest-performing diet consisted solely of diatoms. A contrasting polyunsaturated fatty acid (PUFA) profile was found in post-set clams fed flagellate- or diatom-only diets. Clams fed the bi-algal flagellate diet had a higher percentage of docosahexaenoic acid (DHA) but a lower percentage of (n-6) PUFA, whereas those fed the bi-algal diatom diet had a higher percentage of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) but a lower percentage of DHA. The percentages were similar and neither very high nor very low in clams fed the remaining dietary treatments. The results of this study show that sunray venus post-set clams can be successfully produced when fed a typical hard clam bi-algal flagellate and diatom diet, but they indicate that growth may be accelerated by the addition of other microalgae species.

Choice of microalgae diet affects production outcomes in bivalve hatcheries. This study aimed to identify an optimal microalgae diet to improve hard clam, Mercenaria mercenaria, juvenile production. Four microalgae species (Tisochrysis lutea, Pavlova lutheri, Chaetoceros gracilis and Cyclotella nana) in six dietary combinations were fed for 6 weeks; then, growth, survival and fatty acid profiles of juveniles were evaluated. The highest numerical growth and survival of juveniles were attained by feeding a tetra-species microalgae diet, but no statistical difference was found by feeding bior tri-species diets that consisted of a mix of flagellate and diatom microalgae. Significant differences in fatty acid profiles were found among clams fed different microalgae diets. A contrasting polyunsaturated fatty acid (PUFA) profile was found in juveniles fed flagellate-or diatom-only diets. Clams fed flagellate-only diets contained a higher percentage of docosahexaenoic acid (DHA) but a lower percentage of (n-6) PUFAs, whereas those fed diatom-only diets had a higher percentage of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) but a lower percentage of DHA. In contrast, the percentage of EPA, DHA and ARA was neither very high nor very low in juveniles fed the tetra-species diet. The complementary nutritional profile of the tetra-species microalgae diet resulted in enhanced production and exhibited a more balanced fatty acid profile in clam tissue. The tetra-species microalgae diet should be a preferable choice for feeding hard clam juveniles, but the cost of producing multiple microalgae species for hatchery/nursery operations should be taken into consideration as bi-and trispecies diets provided statistically similar growth and survival. Results of this study can be used to improve productivity and profitability in M. mercenaria hatcheries.