The effect of diet type on growth and fatty acid composition of the sea urchin larvae, II. Psammechinus miliaris (Gmelin)

This study investigated the growth and fatty acid composition of the sea urchin larvae Psammechinus miliaris fed on four types of diets: the microalgae Dunaliella tertiolecta, two types of microencapsulated formulated feed (L and F) and a concentrated algal paste. The fastest growth rate was obtained from D. tertiolecta, but there was no significant difference in larval survivorship between treatments. Larvae fed the formulated feeds showed good growth and survival, although those fed on feed L performed better than those fed on feed F. The metamorphosis rate of competent larvae fed on D. tertiolecta and feed L was not significantly different, but higher than those in the other treatments. Similar post-settlement survival was obtained for larvae fed on microalgae and both formulated feeds, yet 10 d post-settlement juveniles from larvae fed on the formulated feeds were significantly larger. The concentrated algal paste did not support normal growth of the larvae. P. miliaris larvae could grow well on relatively low protein (37% dry weight) and lipid (7% dry weight) D. tertiolecta diet, but high levels of dietary protein and lipid of the formulated feeds may benefit the post-settlement growth of newly metamorphosed juveniles. Dietary fatty acid had a strong influence on lipid composition of the larval tissue. The larvae could incorporate dietary highly unsaturated fatty acids (HUFAs) directly from the formulated feeds, or obtain ARA, EPA and DHA through the elongation of linoleic acid 18:2 n-6 and linolenic acid 18:3 n-3 when fed the HUFA-deficient D. tertiolecta. Higher levels of HUFAs did not seem to act as a growth promoter for the larvae, but a higher concentration of DHA in the formulated feeds may have improved post-settlement growth. An accumulation of PUFA n-3, especially 18:3 n-3, 18:4 n-3, 20:3 n-3 and 20:4 n-3 may promote larval growth. The shortage of PUFA n-3 and PUFA n-6, and especially the lack of non-methylene-interrupted-dienoic fatty acid NMID 20:2 may have impeded the growth of larvae fed on the algal paste. It is suggested that a better formulated feed with improved buoyancy and a more even particle size distribution would improve larval growth.