Effect of nature of dietary lipids on European sea bass morphogenesis: implication of retinoid receptors.

The effect of the nature and form of supply of dietary lipids on larval development was investigated in European sea bass larvae, by considering the expression of several genes involved in morphogenesis. Fish were fed from 7 to 37 d post-hatch with five isoproteic and isolipidic compound diets incorporating different levels of EPA and DHA provided by phospholipid or neutral lipid. Phospholipid fraction containing 1.1 % (PL1 diet) to 2.3 % (PL3 diet) of EPA and DHA sustained good larval growth and survival, with low vertebral and cephalic deformities. Similar levels of EPA and DHA provided by the neutral lipid fraction were teratogenic and lethal. Nevertheless, dietary phospholipids containing high levels of DHA and EPA (PL5 diet) induced cephalic (8.5 %) and vertebral column deformities (35.3 %) adversely affecting fish growth and survival; moreover, a down-regulation of retinoid X receptor alpha (RXRalpha), retinoic acid receptor alpha, retinoic acid receptor gamma and bone morphogenetic protein-4 genes was also noted in PL5 dietary group at day 16. High levels of dietary PUFA in neutral lipid (NL3 diet) first up-regulated the expression of RXRalpha at day 16 and then down-regulated most of the studied genes at day 23, leading to skeletal abnormalities and death of the larvae. A moderate level of PUFA in neutral lipids up-regulated genes only at day 16, inducing a lesser negative effect on growth, survival and malformation rate than the NL3 group. These results showed that retinoid pathways can be influenced by dietary lipids leading to skeletal malformation during sea bass larvae development.