Effects of dietary fish oil levels on growth, lipid metabolism and blood physiology of red drum Sciaenops ocellatus
XU Liang 1,2,3, WEN Haibo 2,3, SUN Guangxing 1,2,3, MA Xueyan 2,3, JIN Wu 2,3, HUA Dan2, GU Ruobo 1,2,3* , XU Pao1,2,3*
1.Wuxi Fisheries College, Nanjing Agricultural University; 2.Key Laboratory of Genetic Breeding and Aquaculture Biology of Freshwater Fishes, Ministry of Agriculture and Rural Affairs, Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences; 3.Sino-US Cooperative Laboratory for Germplasm Conservation and Utilization of Freshwater Mollusks, Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences
Abstract: Juvenile red drum Sciaenops ocellatus with initial body weight of (43.40±6.40)g were reared in 9 net cages (1 m×1 m×1 m) disposed in a cement tank and fed isonitrogen and isoenergetic diets containing 4% (group 4%), 7% (group 7%) and 9% (group 9%) of fish oil at water temperature for 8 weeks when the growth performance, indicators of lipid metabolism, blood parameters and liver histology were investigated in the fish fed the diets containing various levels of fish oil in order to screen the optimal dietary fish oil levels to increase the contents of docosapentaenoic acid and docosahexaenoic acid in the plasma of the red drum. Results showed that there were significantly higher survival rate, body length, and weight gain rate in the fish in groups 4% and 7% fish oil than those in group 9% (P<0.05). The fish fed the diet containing 4% of the fish oil had significantly lower hepatosomatic index and viserosomatic index than the fish fed the diet containing 9% of the fish oil (P<0.05) did, without significant difference between group 4% and group 7%. No significant difference in condition factors and activities of lipase (LPS) and lipoperoxidase (LPO) in intestines were found among the three groups (P>0.05). The liver histological observation revealed that hepatocyte steatosis was positively correlated in extent with the level of dietary fish oil. The blood glucose levels were significantly higher in group 4% and group 7% than that in group 9% (P<0.05), with significantly lower alanine transaminase(ALT) activity in group 4% than that in group 9% (P<0.05). There were significantly higher triglyceride level in group 4% than that in group 9% (P<0.05), without significant differences between group 4% and group 7%, and without significant difference in total protein, total cholesterol and low density lipoprotein (LDL) levels among the three groups (P>0.05). There were (226.72±27.74)mg/L of docosapentaenoic acid and (2470.31±293.51) mg/L of docosahexaenoic acid in group 4%, significantly higher than those in other fishes, without significant difference between group 4% and group 7% (P>0.05). The findings indicated that too much dietary fat (fish oil) inhibited the growth of the red drum, and the activities of enzymes related to fat metabolism, and accelerated the deposition of liver fat, and that the level of docosapentaenoic acid and docosahexaenoic acid in the plasma of the red drum was significantly increased by addition of 4% fish oil with 24% DHA in the commercial feed containing 8.21% crude fat.
2020, Vol. 35 
