Microencapsulated Diets as an Alternative to Bivalve Feeding: Particle Size and Microalga Content Affect Feed Intake

SIMPLE SUMMARY: Bivalve shellfish aquaculture represents a sustainable and nutritionally sound path to provide food for a growing global population. New advances in feed formulation, namely microencapsulation, demonstrated great potential to face key bivalve nutrition problems, enabling increased quality production as the lack of naturally occurring food may result in non-lethal prejudice with losses in organoleptic characteristics. To test the applicability of algae-based microencapsulation, this study evaluated the food intake in five bivalve species that are highly valuable and widely cultivated throughout the world: Pacific oyster, grooved razor shell, carpet shell clam, manila clam, and common cockle. Four microencapsulated diets were implemented, incorporating two different microalgae species into two different diameter pellets. Overall, all the tested diets were easily ingested by the bivalves, although species-related profiles of food intake depending on the pellet size were observed. These results enabled a better selection of feed with appropriate profiles, offering a margin of opportunity to improve bivalve nutritional value and contributing to reinforcing knowledge in the framework of shellfish aquaculture. Moreover, a combination of different microalgae could be explored in the future as it may provide good sources of essential nutrients and a better product for the final consumer. ABSTRACT: Bivalve mollusks represent a nutritious source with a low environmental impact; as a result, they are one of the most attractive aquaculture options. Advances in microencapsulation technology offer great potential to face key bivalve nutrition problems, and an alga-based microencapsulated diet can turn enriched bivalves into potential functional foods. The central goal of this study was the evaluation of food intake as a function of particle size and microalga content following the supply of four microencapsulated diets, incorporating as core material Nannochloropsis sp. or Tetraselmis sp. in 20 or 40 µm diameter pellets (diets N20, T20, N40, and T40, respectively) in five bivalve species (Magallana gigas, Solen marginatus, Ruditapes decussatus, Ruditapes philippinarum, and Cerastoderma edule). Overall, all tested diets were easily ingested, although food intake was higher for N20 (except for the S. marginatus, which showed a higher rate for the diet T40). Concerning a size-related analysis, C. edule and S. marginatus favored, respectively, smaller and bigger pellet-sized diets, with no signs of selectivity for microalga species. The diet T20 was the lesser ingested, except for C. edule. This knowledge enables a better selection of feed with appropriate and species-adjusted profiles, contributing to the optimization of microencapsulated diets for bivalve rearing and a better final product.