The Effects Of Dietary Arachidonic Acid, α-linolenic Acid Levels And Ratio Of α-linolenic Acid To Linoleic Acid On Growth Performance, Fatty Acid Composition And Lipid Accumulation Of Large Size Japanese Seabass(Lateolabrax Japonicus)

This study investigated the effects of dietary fatty acid profiles on the growth performance, serum biochemical parameters, fatty acid composition and lipid accumulation of large Japanese seabass(Lateolabrax japonicus). The experimental diets were fed to triplicate groups of 20 fish. The fish were fed to satiation twice daily for 12 weeks. The feeding trials were conducted in seawater floating net cages, the water temperature ranged from 23 to 30.5 °C, the salinity from 26‰ to 31‰ and the dissolved oxygen content was approximately 6.5 mg L-1 during the experimental period. The results of these studies are shown as follows:1.A feeding experiment was conducted to investigate the optimal level of arachidonic acid(ARA) in the diet of Japanese seabass(mean initial weight 207.16±0.72 g). Six isonitrogenous and isoenergetic diets were formulated with graded levels of dietary ARA, 0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32%, respectively. The results showed that nosignificant differences in survival(93.33%-98.33%) were found among dietary treatments(P>0.05). With the increase of dietary ARA levels, the specific growth rate(SGR) and feed efficiency(FE) increased at first, and then kept steady after reaching their peaks at the 0.37% dietary ARA level(P<0.05). The body composition analysis showed that the whole-body protein content first increased and, then decreased with increasing dietary ARA, while the whole-body lipid content followed the opposite pattern. The activities of glutamic-oxaloacetic transaminase(GOT), glutamic-pyruvic transaminase(GPT) and alkaline phosphatase(AKP) in serum significantly increased when dietary ARA level decreased from 0.05% to 0.37%, and then increased when the dietary ARA level increased from 0.37% to 2.32%(P<0.05). With increasing dietary ARA, the triglycerides(TG) contents in serum showed a significantly increasing tendency(P<0.05), but no significant differences were found in cholesterol(CHOL) contents in serum among dietary treatments(P>0.05). The high density lipoprotein cholesterol(HDL-C) contents in serum significantly increased at first and then showed a declining tendency(P<0.05), but the low density lipoprotein cholesterol(HDL-C) contents in serum had a opposite trend with HDL-C(P<0.05). The fatty acid composition of liver and muscle reflected closely those of diets. These results suggested that based on growth performance, antioxidant function, serum biochemical parameters, and lipid accumulation, the recommended dietary ARA level for large size Japanese seabass was 0.37%-0.60%. These results also strongly suggested that dietary ARA could significantly affect the fatty acid composition and lipid accumulation of large size Japanese seabass.2. A feeding experiment was conducted to investigate the optimal level of α-linolenic acid(ALA) in diets of Japanese seabass(mean initial weight 207.77±0.64 g). Six isonitrogenous and isoenergetic diets were formulated with graded levels of dietary ALA, 0.06%、0.99%、2.03%、3.18%、4.12% and 5.08%(%), respectively. The results showed that the specific growth rate(SGR) and feed efficiency(FE) increased at first, and then decreased with the increase of dietary ALA levels, and reaching their peaks at the 2.03% dietary ALA level(P<0.05). No significant differences were found in survival rate(93.33%-98.33%) among dietary treatments(P>0.05). The body composition analysis showed that the whole-body lipid content increased with increasing dietary ALA, while the liver lipid content increased at first, and then decreased with the increase of dietary ALA levels(P<0.05). The activities of glutamic-oxaloacetic transaminase(GOT) and glutamic-pyruvic transaminase(GPT) in serum significantly increased when dietary ALA level decreased from 0.06% to 2.03%, and then increased when the dietary ALA level increased from 2.03% to 5.08%(P<0.05). With increasing dietary ALA, the triglycerides(TG) and cholesterol(CHOL) contents in serum increased at first, and then decreased, and reaching their peaks at the 4.12% dietary ARA level(P<0.05). The high density lipoprotein cholesterol(HDL-C) contents in serum significantly increased at first and then showed a declining tendency(P<0.05), but the low density lipoprotein cholesterol(HDL-C) contents and the activities of alkaline phosphatase(AKP) in serum had not significant differences(P>0.05). The fatty acid composition of liver and muscle reflected closely those of diets. These results suggested that based on growth performance, antioxidant function, serum biochemical parameters, and lipid accumulation, the recommended dietary ALA level for large size Japanese seabass was 2.03%-3.18%. These results also strongly suggested that dietary ALA could significantly affect fatty acid composition, lipid accumulation and transcription of fatty acid synthesis and oxidation related genes of large size Japanese seabass.3. A feeding experiment was conducted to investigate the optimal ratio of α-linolenic acid to linoleic acid(ALA/LA) in diet of Japanese seabass(mean initial weight 207.29±0.82 g). Six isonitrogenous and isoenergetic diets were formulated with graded ALA/LA, 0.02, 0.19, 0.45, 0.84, 1.48 and 2.73, which were named R-0.02, R-0.19, R-0.45, R-0.84, R-1.48 and R-2.73, respectively. The results showed that the specific growth rate(SGR) increased at first, and then decreased with the increase of dietary ALA/LA, and reaching their peaks at the dietary R-0.84(P<0.05). No significant differences were found in survival rate(93.33%-98.33%),among dietary treatments(P>0.05). The body composition analysis showed that the whole-body and liver lipid content increased at first, and then decreased with the increase of dietary ALA/LA(P<0.05). The activities of glutamic-oxaloacetic transaminase(GOT) and glutamic-pyruvic transaminase(GPT) in serum significantly increased when dietary ALA/LA decreased from 0.02 to 0.84, and then increased when the dietary ALA/LA increased from 0.84 to 2.73(P<0.05). With increasing dietary ALA/LA, the triglycerides(TG), cholesterol(CHOL) and high density lipoprotein cholesterol(HDL-C) contents in serum increased at first, and then decreased, and reaching their peaks at the dietary R-0.84(P<0.05). However, the low density lipoprotein cholesterol(HDL-C) contents and the activities of alkaline phosphatase(AKP) in serum were not significantly differents(P>0.05). The fatty acid composition of liver and muscle reflected closely those of diets. These results suggested that based on growth performance, antioxidant function, serum biochemical parameters, and lipid accumulation, the recommended dietary ALA/LA for large size Japanese seabass was 0.45-0.84. These results also strongly suggested that dietary ALA/LA could significantly affect fatty acid composition, lipid accumulation and transcription of fatty acid synthesis and oxidation related genes of large size Japanese seabass.