Effects of dietary different n-3/n-6 fatty acid ratio on the growth performance and antioxidant capacity of juvenile freshwater giant prawn (Macrobrachium rosenbergii)

An 8-week feeding experiment was conducted to investigate the effects of dietary n-3/n-6 fatty acid ratios on the growth performance, muscle quality, antioxidant capacity, serum physiological indicators and digestibility of Macrobrachium rosenbergii. Five iso-nitrogenous and iso-lipidic diets were formulated with graded levels of n-3/n -6 PUFA(D1: 0.37, D2: 0.59, D3: 0.93, D4: 1.51, D5: 4.38), with four replicates, 40 shrimps each. The results showed that the dietary n-3 PUFA/n-6 PUFA ratio did not significantly affect survival rate (SR). The final weight (FW), weight gain rate (WGR) and specific growth rate (SGR) of the shrimp first increased and then declined with the increase of dietary n-3 PUFA/n-6 PUFA ratio, with the D3 group displaying the highest values. The D3 group also displayed the highest hepatopancreas protease and fatty acid synthetase (FAS) activities. Dietary n-3 PUFA/n-6 PUFA ratio had no significant effect on the muscular crude protein content, moisture and ash content of the shrimp, but the D3 group showed the highest muscular total lipid content which was significantly higher than those of other groups. The variation trend of muscular n-3 PUFA/n-6 PUFA ratio in shrimp was positively correlated with the variation trend of dietary n-3 PUFA/n-6 PUFA ratio. The superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) in hepatopancreas and serum as well as the ceruloplasmin (CP) content in serum first increased and then decreased with the increase of dietary n-3 PUFA/n-6 PUFA ratio and peaked in D3 (0.93) group and D4 (1.51) group, but the content of malondialdehyde (MDA) rose continuously. The content of total cholesterol and triglycerides in the serum of D1 group were significantly higher than those of other group as the dietary n-3 PUFA/n-6 PUFA ratio increased. The activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in the serum of the shrimp first declined and then increased and the D3 group had the lowest values. It is therefore suggested that an appropriate dietary n-3 PUFA/n-6 PUFA ratio significantly improves the growth performance and antioxidant capacity the juvenile prawn M. rosenbergii. Based on Broken-line regression analysis of WGR and SGR, the optimal dietary n-3 PUFA/n-6 PUFA ratio, for growth performance of juvenile freshwater giant prawn M. rosenbergii is 0.86-0.94.