Evaluation of Biorefinery Products From Microchloropsis gaditana, Isochrysis galbana, and Arthrospira platensis in Juvenile Gilthead Seabream (Sparus aurata): Effect on Growth, Nutrient Utilization, Chemical Composition, Metabolism, and Intestinal Functionality.

The present study evaluated the effects of replacing fish oil with microalgal oil on growth performance, nutrient utilization, chemical composition, metabolism and gut functionality in Sparus aurata. Three experimental diets were formulated with increasing levels of oils derived from the microalgae Microchloropsis gaditana and Isochrysis galbana for replacing fish oil: 50% (MO50), 75% (MO75) to 100% (MO100) of total oil. All diets were also supplemented with a protein hydrolysate obtained from Arthrospira platensis to partially replace fishmeal, as well as with an algal carotenoid extract. A total of 198 fish (initial body weight 10.5 ± 0.4 g) were randomly distributed into 12,400 L tanks and fed the experimental diets ad libitum for 83 days under controlled conditions. Growth performance, feed efficiency and somatic indices were assessed, while muscle proximate composition, fatty acid and carotenoid profiles, plasma metabolites, and tissue glycogen were analyzed using standard biochemical and chromatographic techniques. Digestive enzyme activities (trypsin, chymotrypsin, leucine aminopeptidase, alkaline phosphatase) and well as intestinal histology were also evaluated. The results evidenced that use of microalgal oil did not affect fish growth. Fish fed diets supplemented with microalgal products tended to reduce muscle lipid content. Fish fed diets devoid fish oil showed an increase in eicosapentaenoic acid (EPA) content when microalgal oil was included. Plasma cortisol did not vary among experimental groups. The activity of foregut trypsin and alkaline phosphatase increased with the use of microalgal oil, while in the hindgut trypsin and leucine aminopeptidase activities were enhanced. The use of algal products promoted longer intestinal villi and reduced lamina propria thickness in the distal intestine. Overall, the results indicate that total replacement of fish oil with microalgal oil has no detrimental effects on growth performance, and exerts positive effect on specific fatty acids and intestinal functionality.