Nutritional effect of substituting microalgal concentrates with microencapsulated diets in Mytilus galloprovincialis spat

The expansion of mussel aquaculture is limited by the availability of spat and production on land is dependent on costly cultures of microalgae as feed. Substitution of algae with microencapsulated feeds can reduce feed contaminations, ease the storage and extend the shelf life, ensuring stable production of consistent quality at sustainable costs. This study investigated the effects of the substitution of commercial preserved microalgal concentrates (A) with different inclusion levels of Schizochytrium-microencapsulated feed (BioBullets, B) for Mytilus galloprovincialis spat: no substitution, A (100%A; 0%B); low substitution, ABL (40%A; 60%B); medium substitution, ABM (20%A; 80%B); complete substitution, B (0%A; 100 %B). For 8 weeks, spat of <1 cm were cultured under dietary treatments and survival, growth, condition index, digestive gland atrophy and adipogranular cell index were compared, using spat unsupplemented with any feeds as negative control (NC). Diet had a significant effect on spat growth and tissue biochemical and fatty acid composition, demonstrating the assimi-lation of microencapsulated diets. Spat growth was positively correlated with dietary and spat tissue protein, monounsaturated fatty acids and eicosapentaenoic acid content and was highest in spat fed A and ABL. <10% dietary proteins equally sustained M. galloprovincialis spat growth through dietary replacement with higher proportions of lipids (x3) and carbohydrates (x2). With manufacturing improvements, 60% substitution of preserved microalgal concentrates by microencapsulated Schizochytrium can be considered in attempting to enhance economic feasibility in spat production.