High DHA content in Artemia is ineffective to improve Octopus vulgaris paralarvae rearing

We analyzed the performance and biochemical composition of Octopus vulgaris paralarvae fed on three different diets, consisting of Artemia juveniles (1.5-2.8mm) differing in their highly unsaturated fatty acid (HUFA) composition and protein/lipid (P/L) ratio. The live prey were supplied twice a day at equal proportions, with the first daily meal being common to all groups: Artemia enriched with a mixture of the microalgae Rhodomonas lens and Isochrysis galbana (70:30 dry-weight basis). In the second daily meal, the control group (AR+I) was supplied with the same Artemia enriched with microalgae; group AGOLD was fed with Artemia enriched with Ori-Gold (Skretting), a commercial product very rich in docosahexaenoic acid (DHA, 22:6n-3); and group AGOPEL was fed with Artemia enriched with a manually prepared diet rich in protein and in HUFAs. A trend for better survival was observed in group AR+I at 25days of rearing, though no statistical differences were found among groups. The dry weight (DW) and total length (TL) of 15-day post hatch (dph) and 25-dph paralarvae from groups AR+I and AGOPEL were significantly higher than values found for paralarvae from AGOLD (P <0.05). A significant and positive linear correlation was found between paralarval DW and dietary protein/lipid ratio (P <0.01), while no beneficial effects of higher DHA content in Artemia were observed. Regarding the fatty acid (FA) composition of paralarvae, a remarkable drop in DHA was observed in all groups with respect to hatchlings. However, this decrease was more pronounced in paralarvae from AR+I (P <0.05) than in those from groups AGOLD and AGOPEL. Despite this evidence, the best growth and survival rates were observed in group AR+I, which was the only one where 35-dph paralarvae were attained. These data question the nutritional “essentiality” of DHA for paralarvae, and suggest that in order to sustain a good performance of paralarvae a minimum dietary P/L ratio should be attained before the HUFA composition of the diet may play a significant role.