Effect of dietary supplemental l-carnitine on growth performance, body composition and antioxidant status in juvenile black sea bream, Sparus macrocephalus

Effects of dietary l-carnitine were studied in juvenile black sea bream (Sparus macrocephalus). The semipurified basal diet [crude protein 450 g kg⁻¹ dry matter (DM); crude lipid 126 g kg⁻¹ DM] was formulated to choose white fishmeal as the protein source and fish oil plus corn oil (1 : 1) as the lipid source. Six diets (control + diets 1-5) containing 0.1, 0.12, 0.16, 0.24, 0.39 and 1.1 g of l-carnitine kg⁻¹ diet were fed to triplicate groups of black sea bream (initial weight 13.10 ± 0.05 g) for 8 weeks. At the end of the feeding trial, growth performance, body composition and antioxidant status were determined. The results showed that relative growth rate (RGR) was significantly improved by the elevation of dietary l-carnitine level from 0.1 to 0.24 g kg⁻¹, but decreased with further increment (P < 0.05). Lipid content decreased significantly (P < 0.05) in the dorsal muscle whereas increased (P < 0.05) in the liver with the addition of dietary l-carnitine. Dietary l-carnitine supplements elevated enzymatic antioxidants (superoxide dismutase, SOD; catalase, CAT; glutathione-S-transferase, GST) activities (P < 0.05) yet decreased the content of non-enzymatic factor, total sulphydryl groups (TSH) (P < 0.05). In summary, the optimum dietary l-carnitine level was 0.284 g kg⁻¹ diet by second-polynomial regression analysis based on RGR (y = -647.4x² +367.97x + 234.55; R² = 0.977, x = dietary l-carnitine levels, y = RGR), and dietary l-carnitine addition within the levels adopted in our study could depress lipid peroxidation in tissues of juvenile black sea bream.