Abstract:It has been clear that the dietary arachidonic acid (ARA) is essential in the growth of juvenile Japanese seabass (Lateolabrax japonicas), and the requirement of ARA could vary at different growth stages. A 12-week feeding experiment was conducted to investigate the optimal level of ARA in 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. Triplicate groups of 20 fish were fed to apparent satiation twice daily. The water temperature ranged from 23 to 30.5℃, the salinity from 26 to 31 and the dissolved oxygen content was approximately 6.5 mg/L during the experimental period. The results showed that no significant differences in survival rate (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). No significant differences were found in hepatosomatic index (HSI), viscerasomatic indexes (VSI) and condition factor (CF) among dietary treatments (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. With the increase of dietary ARA levels, the activities of superoxide dismutase (SOD) in serum and liver significantly increased at first and then showed a declining tendency (P<0.05), but the malondialdehyde (MDA) contents in serum and liver had a converse trend with SOD (P<0.05). The activities of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) in serum observably decreased when the dietary ARA level increased from 0.05% to 0.37%, and then increased when the dietary ARA level increased from 0.37% to 2.32% (P<0.05). The broken-line model analysis based on SGR and FE indicated that the optimal level of dietary ARA for Japanese seabass of (207.16±0.72) g of the diet was 0.37%.
