Expression of genes related to long-chain (C18-22) and very long-chain (> C24) fatty acid biosynthesis in gilthead seabream (Sparus aurata) and Senegalese sole (Solea senegalensis) larvae: investigating early ontogeny and nutritional regulation

Long-chain polyunsaturated fatty acids (LC-PUFA) have been extensively studied in aquaculture due to their importance for survival and development in teleosts. However, very long-chain polyunsaturated fatty acids (VLC-PUFA) have been practically unexplored within the aquaculture scenario. VLC-PUFA, although always present in small amounts, can be pivotal for the correct development and function of tissues such as retina, brain and gonads of vertebrates including fish. This study aimed at determining the temporal expression patterns of genes involved in the biosynthesis of VLC-PUFA (elov14a, elov14b) and their precursors, LC-PUFA, (fads2, elov15) during the early ontogeny of Solea senegalensis and Sparus aurata. Furthermore, we investigated the nutritional regulation of these genes in early life-cycle stages of fish fed low and high LC-PUFA diets consisting of non-enriched and enriched live preys (Brachionus plicatilis and Artemia franciscana), respectively. The effect of dietary LC-PUFA on growth and fatty acid composition was also examined. The results obtained during early development reveal that all genes studied are expressed before the hatching stage. There is a consistency between the timing at which retinogenesis occurs in both species and an increase of the expression of the two elov14 responsible for the synthesis of VLC-PUFA. The results obtained in nutritional assays for both species suggest that the expression of the two isoforms of elov14 (isoform a in early larvae, and b in late larvae) can be regulated positively according to the dietary content of LC-PUFA in early stages, which could activate the VLC-PUFA biosynthesis even during short-term feeding periods (seven days). The body part analysis in late larvae of both species revealed that both isoforms of elov14 are expressed preferentially in the head. This can be associated to their highest presence in the neural and visual tissues.