Effects of dietary l‐carnitine supplementation on growth and lipid metabolism in European seabass (Dicentrarchus labrax)

In most vertebrates, the β-oxidation of long-chain fatty acids is stimulated by the presence of l-carnitine, which allows long-chain acyl-CoA-esters to cross the mitochondrial membrane. A study was undertaken to investigate the possible effects of supplemental dietary l-carnitine on the growth, tissue lipid content and activity of hepatic acetyl coenzyme-A carboxylase (ACoAC) in the European seabass (Dicentrarchus labrax). Four isoproteic (42% crude protein), isolipidic (19% crude fat) and isoenergetic (21.5 kJ g−1) diets were formulated to contain increasing levels of carnitine (0.3, 1.1, 2.0 and 3.0 g kg−1). Triplicate groups of 25 seabass (mean body weight: 250 g) were grown in seawater (temperature: 20 °C; salinity: 35 ppt) over 85 days. At the end of the growth study, whole body, liver, viscera, gonads, muscle and plasma samples were withdrawn for analyses. Dietary l-carnitine supplementation did not significantly affect weight gain, feed efficiency or protein utilisation. At the end of the experimental period, the whole body composition of fish did not differ significantly between experimental treatments. Similarly, neither total plasma triacylglycerols and cholesterol levels nor tissue lipid content were affected by the dietary l-carnitine supplementation. By contrast, fish fed the l-carnitine supplemented diets showed a three-fold increase in the activity of ACoAC, suggesting higher rates of lipogenesis in seabass liver. The overall results show that supplemental dietary l-carnitine is not suitable for reducing fat deposition in seabass fed high-fat diets.