Effects Of Oxidized Fish Oil On Growth Performances And Antioxidant Abilities In Juvenile Grass Carp(Ctenopharyngodon Idellus)

Three chapters were included in this thesis, to investigate the effects of oxidized fish oil on growth performance, antioxidant enzyme activities and the relative expression of antioxidant enzymes mRNA of juvenile grass carp(Ctenopharyngodon idellus). An 8-week feeding trial on juveniles(average weight of 30.0 ±2.68 g) was conducted in quadruplicate groups, 3 replicates in per group, and 17 juvenile grass carp in each replicate. Four isonitrogenous and isocaloric diets were formulated utilizing fresh fish oil(peroxide value: 9.07 meqO2/Kg) and oxidized fish oil(peroxide value: 49.72, 144.64, 345.45 meqO2/Kg) as the lipid source respectively, fed four groups, and named Control group(F), Mild oxidation group(P1), Middle oxidation group(P2), Heavy group(P3), the diet prepared with fresh fish oil served as control. The results showed that :(1)Oxidized fish oil(peroxide value: 49.72, 144.64, 345.45 meqO2/Kg) increased HSI significantly(P <0.05), decreased CF significantly(P <0.05), the weight gain and specific growth rate of juvenile grass carp decreased significantly(P<0.05)(2)Oxidized fish oil increased the content of MDA in the body tissues, and decreased the activities of antioxidant enzymes. Compared to the control, Mild oxidized fish oil increased the level of MDA in kidney,significantly(P<0.05); decreased the levels of T-AOC in serum, liver, intestine significantly(P<0.05); decreased the activity of SOD in liver, muscle,and CAT in serum, liver, muscle significantly(P<0.05). In P3 group(POV: 345.45 meqO2/Kg), the levels of MDA in serum, liver, kidney, intestine was increased significantly(P<0.05), the levels of T-AOC in serum, liver, kidney, muscle, intestine was decreased significantly(P<0.05), as well as the activity of SOD in serum, liver, kidney, muscle, CAT in serum, liver, muscle decreased significantly(P<0.05). However, the activity of GSH-PX showed no differences(P>0.05). The activity of main antioxidant enzymes distributed as follows, SOD: serum>liver>kidney>muscle; CAT: liver>kidney>serum>intestine>muscle; GSH-PX: liver>serum>kidney>intestine; MDA: serum>intestine>muscle>liver>kidney; T-AOC: liver>serum>intestine>kidney>muscle. [Conclusions] Oxidized fish oil could increase the level of MDA, decrease the ability of antioxidant, induce oxidative stress of juvenile grass carp. There was a tissue-specific of antioxidant enzyme activity and MDA content in different tissues of juvenile grass carp. The antioxidant enzymes in liver has higher activity and more sensitive to oxidative stress induced by oxidized fish oil than other tissues.(3)Oxidized fish oil significantly decreased the expression of SOD mRNA and GCLC mRNA in hepatopancreas, kidney and dorsal muscle tissues(P< 0.05); three degree of oxidized fish oil significantly reduced CAT expression mRNA of kidney and muscle, severe oxidized fish oil significantly reduced the expression of CAT mRNA in hepatopancreas(P< 0.05); severe oxidized fish oil significantly reduced expression of GSH-PXmRNA in dorsal muscle, and the GSH-PX mRNA expression were significantly increased in mild and moderate oxidation of fish oil groups.In this study, Oxidized fish oil decreased growth performance,could increase the level of MDA, decrease antioxidant enzyme activities and the relative expression of antioxidant enzyme mRNA,decrease the ability of antioxidant, induce oxidative stress of juvenile grass carp.The damage of oxidized fish oil(345.45 meqO2/kg) is most serious.Although oxidized fish oil(49.72, 144.64 meqO2/kg) did not impair the growth performance, its oxidation resistance had declined obviously. The damage of oxidized fish oil for juvenile grass carp may caused by the body lipid peroxidation and antioxidant enzyme gene expression. The harm of oxidized fish oil to the grass carp larval,which warning to control the aquatic animal feed oil quality and to prevent the oxidation of fat intake strictly.