Assessment of microalgae concentrate as diet for hard clam, Mercenaria mercenaria , larvae

The on-site culture of live microalgae represents a major challenge for bivalve hatchery operations due to high cost and labour demands. This study evaluated the efficacy of commercially available microalgae concentrates as a partial or complete replacement diet for live microalgae for culture of the hard clam, Mercenaria mercenaria, larvae. Larvae were fed from D-larval stage to post-set, 2–14 days post fertilization (DPF). Larvae fed the complete replacement diets were significantly smaller than those fed partially replaced or live microalgae diets. Foot development was significantly delayed in larvae fed complete replacement diets compared to partially replaced or live microalgae diets. Although early survival (at 5 DPF) was similar among the treatments, final survival (at 14 DPF) varied significantly among treatments. The average final survival was 69%–77% for larvae fed live microalgae, 60%–61% for larvae fed partially replaced diets and 14%–16% for larvae fed complete replacement diets. These results suggest that a live microalgae diet could be partially replaced by a concentrate to feed hard clam larvae. However, complete replacement diet may be used only for a short duration (up to 3 days) without affecting survival.