Abstract:An 8-week feeding trial was conducted in a recirculated system to study the effect of dietary n-3/n-6 long-chain polyunsaturated fatty acid (LC-PUFA) ratios (29.54, D1; 23.04, D2; 18.97, D3; 9.06, D4; 6.86, D5; 3.87, D6) on growth performance, whole-body fatty acid composition, and serum biochemical indices in turbot (Scophthalmus maximus). Six diets were formulated to feed six groups of juvenile turbots [mean initial weight (12.18±0.01) g]. Each diet was randomly fed to triplicate groups of 35 fish per tank. There were no significant differences in the survival rate (SR) of turbot (P>0.05). With decreasing dietary n-3/n-6 LC-PUFA ratios, the weight gain rate (WGR) first increased and then decreased. The WGR of the D6 group was significantly lower than that of the other groups (P<0.05). The lipid deposition rate (LR) reduced with decreasing dietary n-3/n-6 fatty acid ratios, and the D6 group achieved 14.80, which was significant lower than that of the other group (P<0.05). The trypsin content increased as the dietary n-3/n-6 LC-PUFA level decreased from 29.54 to 9.06, and then decreased. Lipase increased with decreasing n-3/n-6 LC-PUFA. As the dietary n-3/n-6LC-PUFA level decreased, fatty acid synthetase and glucose-6-phosphate dehydrogenase first increased and then decreased. When the dietary n-3/n-6 LC- PUFA level was 9.06, fatty acid synthetase levels were significantly higher than those in the other groups (P<0.05). Additionally, glucose-6-phosphate dehydrogenase levels were significantly higher than those in the other groups (P<0.05) when the dietary n-3/n-6 LC-PUFA level was 18.97. Aspartate aminotransferase, total protein, albumin, and high-density lipoprotein cholesterol first increased and then decreased with increasing dietary n-3/n-6 LC-PUFA ratios. These results indicate that, with decreasing dietary n-3/n-6 LC-PUFA ratios, resulting in reduced lipid deposition rate of juvenile turbot.
