The sunray venus clam (SRV) Macrocallista nimbosa is an alternative species to hard clam Mercenaria mercenaria production in Florida due to similar culture techniques. Tropical storms, hurricanes, and contamination can affect live microalgae production in hatcheries, therefore use of alternative feeds, such as microalgal concentrates, should be considered for emergency situations or to alleviate labor and costs associated with live microalgae production.
This study explored whether 2-week post-set SRV (0.83 mm) and hard clams (0.89 mm) could be reared on partial or complete live microalgae replacement diets. Experimental treatments consisted of two live microalgae, two 50% partial replacement and two 100% algal concentrate diets (Table 1). Survival and growth were assessed at six weeks. Fatty acid profiles of clams from each treatment group, live algae and concentrates, were also analyzed.
There was a significant interaction between the effects of clam species and diet on survival, F(5, 24)=24.1, P < 0.05, as well as growth, F(5,708)=26.1, P < 0.05. For both species higher survival and growth was seen with live and partial replacement diets, and hard clams performed better with partial and complete replacement diets than SRV clams. Highest survival was seen in T2 (75%, 68%) and T4 (78%, 76%) and lowest survival in T6 (30%, 45%), in SRV and hard clams, respectively. Highest growth was seen for SRV clams fed live microalgae, and for hard clams in treatments T2 and T4. SRV clams showed lowest growth in T6 and hard clams showed lowest growth in T5.
Clam fatty acid profile was treatment dependent, and although overall trends were similar significant differences between species were seen. The fatty acid profile of clams in T1, T3 and T5 was similar, yet production was highest in the live algae treatment, and higher in the partial than the complete replacement diet. Increased clumping and settlement of the non-motile concentrates was noted and likely accounted for the decreased production. Although partial replacement diets may be a viable option when live algae production is insufficient, a complete replacement of live algae is not recommended for post-set clams.