Microchloropsis salina grown in waters from a bivalve plant accumulates lipids for Ruditapes philippinarum feeding

Microalgae of the Microchloropsis genus accumulate lipids and are studied for exploitation in the food/feed sector. Aquaculture, including mollusc farming, represents a fast-growing field that uses microalgae as live feed. Since microalgal cultivation and aquaculture are water-consuming, in molluscs' indoor rearing plants the re-use of water effluents is a need. In this perspective, Microchloropsis salina was chosen to test the feasibility of reusing the water recirculating in an indoor bivalve hatchery. M. salina was cultivated in static conditions in hatchery wastewater (HW) and in control synthetic media. During algal cultivation, growth, photosynthetic parameters, morphology, protein and lipid contents were evaluated. The fatty acid profile was also analysed. Besides the finding that growth kinetics and productivity were comparable, a lower efficiency in photosynthetic electron flow, accompanied by a different pigment content, characterized M. salina algae cultivated in HW. In parallel, treated algae accumulated large lipid globules and produced acidic exo-mucopolysaccharides. Lipid and fatty acids analyses highlighted interesting differences between control and treated algae, with higher lipid content, similar saturated fatty acid and monounsaturated fatty acid, but lower polyunsaturated fatty acid in HW-treated algae. Feeding tests performed on Manila clam indicated a good degree of acceptability of the alga deriving from both culturing condition.