Effects of different mono, bi and trispecific microalgal diets on survival, growth, development, settlement and fatty acid composition of mussel Mytilus galloprovincialis (Lamarck, 1819) larvae

Based on the microalgae Isochrysis galbana clone T-iso (Ti), Chaetoceros gracilis (Cg) and Tetraselmis suecica (Ts), in the present investigation 8 different feeding regimes were trialed for Mytilus galloprovincialis larval culture: starvation, 3 monospecific diets (Ti; Cg; Ts), 3 bispecific diets (Ti + Cg; Ti + Ts; Cg + Ts) and the trispecific diet Ti + Cg + Ts. The effect of these feeding regimes on several culture parameters (survival, growth, development, competency and settlement) was assessed, and total lipid and fatty acid composition of larvae were analyzed. Our results revealed that specimens were not able to feed on Ts during their earliest development phases, and cultures deprived of ingestible food showed signs of starvation at 8-9 days post fertilization. The diets Ti + Cg, Cg + Ts and Ti + Cg + Ts showed better results than the rest in one or more culture parameters. Although the presence of Cg in a mixed diet seemed to be advantageous, the monospecific diet Cg entailed unexpected larval crushes as well as competency and settlement impairments. The comparative analysis of fatty acid compositions of larvae and diets provided showed that: (i) larvae have a certain capacity for fatty acid regulation, including some de novo biosynthesis; (ii) larvae seem to gain new synthesis capacities with metamorphosis, and (iii) the lack of some polyunsaturated fatty acids (especially docosahexaenoic acid), together with excessive levels of arachidonic acid, might have caused the poor results obtained with the monospecific diet Cg.