Long-Term Effects of a Short Juvenile Feeding Period with Diets Enriched with the Microalgae Nannochloropsis gaditana on the Subsequent Body and Muscle Growth of Gilthead Seabream, Sparus aurata L.

SIMPLE SUMMARY: Currently, microalgae are used as a partial substitute for fishmeal and fish oil in fish diets, but it is unknown if this can influence the long-term growth of the fish. In the present work, we have studied the long-term effects of diets enriched with the microalgae Nannochloropsis gaditana that were supplied to juvenile gilthead seabream, Sparus aurata, at two inclusion levels (2.5 and 5%), either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups), for three months. Subsequently, all groups were transferred to a microalgae-free diet until commercial size was reached (1.6-year-old, ≈27 cm and ≈300 g). The results showed that three-month microalgae supplementation of the diets in juvenile fish had a long-term influence on the final body and muscle growth, as well as in the fibrillar constitution of the myotome. This influence depended on the state (raw versus hydrolyzed) and the microalgae inclusion levels in the diet, in such a way that the hydrolyzed diet mainly increased muscle growth and hyperplasia of the specimens, and this was greater at higher inclusion levels. The fact that microalgae inclusion in the juvenile diet can improve subsequent growth may be advantageous for fish farmers. ABSTRACT: Currently, microalgae are used in fish diets, but their long-term growth effect is unknown. In this experiment, juvenile seabream specimens were fed with microalgae-enriched diets for three months, and then transferred to a microalgae-free diet for 10 months to assess long-term effects up to commercial size (≈27 cm and ≈300 g). The juvenile diets contained Nannochloropsis gaditana at 2.5 or 5% inclusion levels, either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups). The body length and weight were measured in 75 fish group(−1) at commercial stage. The size, number, and fibrillar density of white muscle fibers and the white muscle transverse area were measured in nine fish group(−1) at commercial stage. The results showed the highest body weight in H5 at commercial stage. The white muscle transverse area and the white fibres hyperplasia and density also showed the highest values in H5, followed by H2.5. In contrast, the highest hypertrophy was observed in C and R2.5, being associated with the lowest muscle growth in both groups. These results showed a microalgae concentration-dependent effect in hydrolyzed diets as well as an advantageous effect of the hydrolyzed versus raw diets on the long-term growth of Sparus aurata.