Experiments on the artificial regulation of the amino acid and fatty acid contents of food organisms to meet the assessed nutritional requirements of larval, post-larval and juvenile Dover sole [ Solea solea (L.)

Abstract

The probable amino acid and fatty requirements of larval Dover sole [ Solea solea (L.)] were assessed by analysis of the amino acid and fatty acid content of the yolk of Dover sole eggs. The amino acid and fatty acid contents of the brine shrimp, Artemia salina, and the the rotifer, Brachionus plicatilis, were analysed to assess their suitability for rearing sole larvae. The fatty acid composition of the egg yolk was found to be dominated by large quantities of fatty acids of the 22:6 ω3 series, but these were present only in trace amounts in Artemia and Brachionus. Similarly, the amino acid proline, which is present in the yolk in significant quantities, is almost completely absent from both the food organisms. Experiments were carried out, using fatty acid enriched media to rear yeast species under a variety of conditions, to establish whether the yeasts might absorb some of the molecules required by the sole larvae so that these molecules could then be transferred to the food species by feeding them on the enriched yeasts. It was found that whilst the total lipid content of the yeasts could not be significantly increased, their fatty acid composition was influenced by the culture media. It was also found that the fatty acid composition of the yeasts was reflected in the fatty acid composition of the Artemia cultured on them, although the larger molecules were absorbed less readily. Trials showed that growth rates of Dover sole larvae were significantly increased by the addition of ω3 or 18:3 ω3 fatty acids to the yeasts used to feed Artemia. Brachionus alone proved to be an inadequate diet for the sole larvae. In terms of amino acid composition, decapsulated Artemia cysts appeared to be a promising food, but unfortunately these were not readily digested by the sole larvae.