Nutritional components affecting skeletal development in fish larvae

Marine fish larvae undergo major functional and morphological changes during the developmental stages and several factors can interfere with the normal development of larvae and affect fry quality. Skeletal malformations, such as spinal malformation—scoliosis, lordosis, coiled vertebral column-, missing or additional fin rays, bending opercle or jaw malformations, are frequently observed in hatchery-reared larvae. This paper reviews the effects of some nutritional components on skeletal development in larvae of a number of fish species. In the dietary lipid fraction, for instance, it was proven that the phospholipid concentration affected the spinal malformation rate in sea bass fed a compound diet from mouth opening onwards. Phosphatidylinositol, in particular, seems to prevent skeletal deformities. Highly unsaturated fatty acids, and particularly DHA enrichment in live prey, induce a decrease of opercular deformities in milkfish. It is known that highly unsaturated fatty acids have profound effects on gene expression, leading to changes in metabolism, growth and cell differentiation, and these effects are worth investigating in developing fish. The nature of the dietary protein fraction also affects the quality of fish larvae development. It appears that dietary incorporation of 20 amino acid peptides or diand tripeptides leads to a reduction of spinal malformations in sea bass. Among vitamins, the teratogenic effect of retinoic acid is now well documented in vertebrates. High dietary retinoic acid levels result in higher incidence of bone deformities, such as vertebral curvature, central fusion and compression of vertebra in Japanese flounder larvae. The teratogenic effect of retinoic acid observed in embryonic and postembryonic stages was explained by a depression of shh expression. As for vitamin C, opercular abnormalities in milkfish larvae, associated with distortion of gill filament cartilages, were reduced by 50% when feeding larvae with ascorbic acid enriched rotifers and Artemia, compared to control fish.