A microalga is better than a commercial lipid emulsion at enhancing live feeds for an ornamental marine fish larva

High mortality during larval rearing is a persistent bottleneck in finfish aquaculture and is often caused by inadequate nutrition. Nutritional deficiencies in live feeds are usually overcome by enrichment with commercial lipid emulsions; however, enriching live feeds using microalgae may be more effective. This study investigated the efficacy of the microalga Proteomonas sulcata as a live feed enhancement for rearing larvae of the wide-band anemonefish, Amphiprion latezonatus. We found A. latezonatus larvae fed live feeds enhanced with P. sulcata had higher survival and better growth at 7 days post hatch (dph) compared to fish fed live feeds enriched with a commercial lipid emulsion or left unenriched. At 14 dph, A. latezonatus initially fed rotifers cultured on P. sulcata for several generations had the highest survival overall. These results may be due to the high phospholipid content in rotifers enhanced on P. sulcata compared to other diets. Survival, length, depth, and eye diameter of 7 dph A. latezonatus was also positively correlated with omega-6 docosapentaenoic acid (DPAn-6, 22:5n-6) and high ratios of DPAn-6 to docosahexaenoic acid (DHA, 22:6n-3) in their tissues, highlighting the need to better understand the role of DPAn-6 in larval fish ontogeny. Surprisingly, given their high survival and growth, A. latezonatus larvae fed P. sulcata enhanced live feeds had lower levels of DHA compared to the more poorly performing fish fed the commercial lipid emulsion enriched live feeds; this challenges the paradigm of a positive correlation between DHA and growth and survival that is documented in many other marine fish larvae. This study demonstrates the benefits of using P. sulcata to enhance the nutritional quality of live feeds and highlights the need for a better understanding of the role of n-6 long-chain polyunsaturated fatty acids in the early development of larval fish.