A review of the nutritional effects of algae in marine fish larvae

In the first-feeding of larval, turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus), microalgae are used in the production of rotifers (Brachionus plicatilis) in order to transfer essential nutrients from the algae to the live food. In addition, the algae may be given directly to the larvae along with the live food. In this circumstance they act both as food for the fish larvae and for the live food. Microalgal addition to the first-feeding tanks along with the rotifers improved growth and survival of larvae, whereas short-term enrichment of rotifers with algae did not improve growth and survival of larvae in tanks without algae added. The algae in larval tanks tended to modify and stabilize the nutritional quality of the rotifers in the period before they were consumed by the larvae. The lipid content and fatty acid composition of the rotifers reflected the composition of the algal diets, and the algal species used may be an effective tool to control the fatty acid content (especially DHA, 22:6n−3, docosahexaenoic acid, and EPA, 20:5n−3, eicosapentaenoic acid). The content of n−3 polyunsaturated fatty acids varied between algal species, and to some extent, with the growth limitation of the algal cells. Young stages of marine fish larvae ingested microalgae, but the algal cells were assimilated to a different extent in halibut and turbot. The ingested microalgae may have triggered the digestion process or contributed to the establishment of an early gut flora. The algae in larval tanks most probably modified the bacterial flora of the water and the rotifers. In addition, the algae in larval tanks may have modified the light milieu for the larvae.