Effect of Microalgal Diets on Sunray Venus Clam (Macrocallista nimbosa) Production and Fatty Acid Profile

Abstract

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.