Critical levels of essential fatty acids for normal pigmentation in Atlantic halibut (Hippoglossus hippoglossus L.) larvae

Abstract

High levels of n-3 polyunsaturated fatty acids and a low level of arachidonic acid (ARA, 20:4n-6) in larval diets seem to be necessary for normal pigmentation of Atlantic halibut juveniles, whereas energy status and fatty acid composition seem to modulate eye migration in flatfish in general. However, we do not know the limits or the critical combinations of essential fatty acids that will give normal development of the larvae. In the present study we fed Atlantic halibut larvae enriched Artemia with small differences in fatty acid composition. Artemia enriched with the high TAG (triacylglycerol) emulsion contained average eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) of 13.9 and 12.5% of total fatty acids, respectively, while in Artemia enriched with the high MAG (monoacylglycerol) emulsion, the levels were 12.9 and 9.4%. The fatty acid composition of the larvae reflected the composition of Artemia, in addition ARA was slightly lower in the high TAG than in the high MAG enriched Artemia, i.e. 3.7–4.0 and 4.2–4.3% of total fatty acids, respectively. There were no differences in lipid level, measured as fatty acid methyl esters, neither between the Artemia types, nor between the larval groups. The percentages of normal pigmentation in Atlantic halibut juveniles that had been fed the high TAG and high MAG enriched Artemia were 77±2 and 46±16%, respectively, the eye migration was also slightly better in the high TAG group, but the final weight was lowered from 1.98±0.17 g in the high MAG group to 1.56±0.13 g in the high TAG group. There was a correlation between pigmentation and eye migration, since fish where the left eye had passed the mid-dorsal ridge did not get pigmentation on the blind side. It is concluded that DHA in larval whole body should be higher than 13% of total fatty acids to obtain normal pigmentation in Atlantic halibut larvae when the EPA:ARA ratio is approximately 3.5. The differences in fatty acid composition in the present study had only minor effects on eye migration.