New microalgae for the Pacific oyster Crassostrea gigas larvae

The number of microalgae of high nutritional value actually available to mollusc hatcheries is limited to a few species and this represents a constraint for the industry. Fifteen microalgal species belonging to seven different taxonomic classes were selected from the Algobank-Caen microalgal culture collection of the University of Caen. An initial screening of these microalgae, based on their cytomorphological characteristics and growth performances, led to the selection of four species (Imantonia rotunda, Emiliania huxleyi, Pseudoisochrysis paradoxa and Diacronema vlkianum), which were then tested as food for Crassostrea gigas larvae. Two species (I. rotunda and E. huxleyi) were of poor food value for oyster larvae, while P. paradoxa and D. vlkianum resulted in high growth rate and low mortality. These two microalgae were then characterised (dry weight, ash, gross composition, fatty acids) at different stages of growth and their productivity in standard hatchery conditions (2-l glass carboys, 300-l cylinders) was assessed in order to evaluate the potential of these species for use in commercial hatcheries.