Effect of different dietary polar lipid levels and different n - 3 HUFA content in polar lipids on gut and liver histological structure of gilthead seabream (Sparus aurata) larvae

Abstract

In a previous study feeding larval gilthead seabream on microdiets, an improved growth rate was observed when dietary n−3 HUFA (n−3 highly unsaturated fatty acids) were contained in the polar lipid fraction. A beneficial effect of dietary lecithin on n−3 HUFA incorporation to the larval polar lipids was also observed. To confirm those results and in order to obtain additional information on larval gut and liver histological structure, 11-day-old larvae were fed 4 microdiets differing in lipid composition. In diets N′ and NL′, the main sources of n−3 HUFA were neutral lipids, and polar lipids in diets P′ and PL′. Three lecithin levels were tested, being the highest in diet NL′ and the lowest in diet P′. The total n−3 HUFA level in diets N′ and NL′ was enough to meet the essential fatty acid requirement of larval gilthead seabream obtained in a previous study with a triacylglyceride based diet, while diets P′ and PL′ had a total n−3 HUFA level lower than the minimum determined. A reduction in the larval essential fatty acid requirement to 1.5% d.w. was obtained by feeding dietary n−3 HUFA present in the polar lipid fraction. Feeding larvae with microdiets with low polar lipid levels produced an accumulation of lipid droplets in the enterocytes and a high number of lipid vacuoles in the hepatocytes producing nuclear migration and suggesting a need of dietary polar lipid for lipid transport.