The Physiological Response Of Snakehead (Channa Argus) To Dietary Starch Levels And Phospholipid Levels

Research 1: Effects of dietary starch levels on growth performance,hepatic proximate composition and non-specific immunity of snakehead(Channa argus)The present study aimed to investigate the effects of dietary starch levels on growth performance,hepatic proximate composition and non-specific immunity of juvenile snakehead(Channa argus).Seven isonitrogenous and isolipidic diets,supplemented with graded levels of α-starch,0%,3.0%,6.0%,9.0%,12.0%,15.0% and18.0%,were fed to triplicate groups of juvenile snakehead(initial body weight,11.83± 0.02 g)for 8 weeks.Results showed that dietary starch levels had no significant effect on the growth performance of snakehead,while the survival rate was significantly elevated when the inclusion level of starch was higher than or equal to 9%.The content of hepatic crude protein and crude lipid was significantly reduced with the increase in dietary starch levels,while hepatic glycogen content was significantly elevated,which was partly related to the significantly increased hepatosomatic index and viscerosomatic index.The content of malondialdehyde and serum aspartate aminotrans-ferase and aspartate aminotransferase activity was significantly elevated,while serum lysozyme activity was significantly decreased when dietary starch inclusion content exceeded 9%.Gene expression analysis revealed that the inclusion of starch exceeded9% significantly promoting the expression of NF-κB P65.Meanwhile,the increase in dietary starch levels led to an increased expression of pro-inflammation factor,IL-1βand COX-2,and their expression in 15% and 18% starch inclusion groups was significantly higher than that in the 0% and 3% starch inclusion groups.In conclusion,the recommended dietary starch inclusion level is 11.46% based on the reasonable compromise of the above biomarker responses.Research 2: Effects of dietary phospholipid levels on growth performance,antioxidative status and lipid deposition of juvenile snakehead(Channa argus)This study was conducted to investigate the effects of dietary phospholipids on growth performance,antioxidant capacity,fatty acid composition and lipid metabolism of juvenile snakehead(Channa argus).Five isonitrogenous(56.2%)and isolipidic(16.8%)diets(PL0,PL2,PL4,PL6 and PL8)with phospholipid levels of1.37,3.22,5.36,7.23 and 9.15% were used,with three replicates in each group.Juvenile snakeheads with an initial body weight of 3.99 ± 0.01 g were fed for 43 d.The results showed that the addition of phospholipids to the diets significantly affected the growth performance of juvenile snakeheads(P < 0.05).With the increase of phospholipid level in the feed,the daily feeding rate(FI)and feed conversion efficiency(FCR)showed a trend of first decreasing and then increasing,with the minimum value of FI in the PL4 group and the minimum value of FCR in the PL6 group,both of which were significantly lower than the control group(P < 0.05);meanwhile,the HSI in the PL8 group was significantly smaller than the other treatments(P < 0.05).The increase of phospholipid content in the feed significantly reduced the crude fat content of whole fish and liver(P < 0.05),while moisture showed the opposite trend(P < 0.05).MDA content in livers of juvenile fish showed a significant decrease(P < 0.05)with increasing phospholipid content in the diet;SOD activity increased significantly(P <0.05);T-AOC showed a trend of increasing and then decreasing,with the PL2 group being significantly higher than all other groups except the PL6 group(P < 0.05);CAT activity was not affected by the change in phospholipid content in the diet(P > 0.05).The addition of phospholipids to the feed significantly increased the n-3 PUFA content in whole fish and liver of juvenile fish(P < 0.05).The addition of phospholipids to the feed significantly inhibited the expression of the lipogenesis-related gene ACC1 in the liver(P < 0.05);promoted the expression of the lipolysis-related genes MGL and HSL(P < 0.05);meanwhile,the expression of fatty acid oxidation genes PPARα,CPT1 and ACO in the PL6 group was significantly higher than that in the control group(P < 0.05).In conclusion,the addition of phospholipids to the feed can improve the growth performance of juvenile snakeheads,improve antioxidant capacity and significantly reduce lipid deposition by regulating lipid metabolism,and the optimal requirement of phospholipids in the feed is 5.36% based on the growth index.