Effects Of Dietary L-carnitine Supplementation On Growth Performance And Antioxidant Capacity In Phoxinus Lagowskii Dybowski

In the condition of modern aquatic intensive culture,there are many environmental factors including water pollution,ammonia nitrogen,temperature and many human factors including breeding density increase and feed nutrition imbalance can often lead to aquatic animals in a stress state.L-carnitine is an additive with a variety of physiological functions.The main function is to promote the ?-oxidation of fatty acids into mitochondria as a carrier.It can enhance the growth performance and antioxidant capacity of aquatic animals.Phoxinus lagowskii Dybowski is one of the major aquaculture varieties in Jilin Province.The nutritional requirements of Phoxinus lagowskii Dybowski are still lacking,and the study on the growth performance and antioxidant properties of L-carnitine in Phoxinus lagowskii Dybowski is blank.In this paper,four parts were designed to explore the effects of L-carnitine on the growth performance,antioxidant properties and Keap1-Nrf2-ARE signaling pathway in Phoxinus lagowskii Dybowski.Five isonitrogenous(36.47 %)and isoenergetic(17.59 MJ/kg)diets contained five doses of L-carnitine(0(control),50,400,750 and 1100 mg/kg diet)were fed to fish for 120 days.Fish(19.28 ± 0.23 g)were randomly divided into five treatments(90 fish per group)and experiment was conducted in triplicate(thirty fish per replica).Collecting samples every 30 days once throughout the 120 day period.The results indicated that:(1)Under this test condition,Phoxinus lagowskii Dybowski fed 400 mg/kg of L-carnitine significantly increased final weight,WGR,SGR,PER and FER at every period(P>0.05);750 mg/kg L-carnitine group significantly increased final weight,WGR and SGR at the 60 th,the 90 th and 120 th days(P>0.05).The final weight,WGR and SGR of 50 mg/kg L-carnitine group were significantly higher than those of control group at the 120 th days(P>0.05).At the 120 th days,the BCI of 400 and 750 mg/kg L-carnitine groups were significantly higher than that of the control group(P>0.05).The addition of L-carnitine had no significant effect on the ESR(P>0.05).The optimal dosage of L-carnitine was 530 mg/kg.(2)Among treatments,the 50,400 and 700 mg/kg L-carnitine groups,T-AOC levels in serum and hepatopancreas at the 90 th and 120 th days were significantly increased(P>0.05).T-GSH levels were significantly increased in 750 mg/kg L-carnitine group in serum,400 and 750 mg/kg L-carnitine groups significantly increased T-GSH level in hepatopancreas for 90 th and 120 th days(P>0.05).At the 60 th,90th and 120 th days of the trial,T-SOD activity was significantly improved in serum of 750 mg/kg L-carnitine group and in hepatopancreas of 50-400-750-1100 mg/kg L-carnitine groups(P>0.05).Fish fed 400 and 750 mg/kg L-carnitine significantly increased the activity of GSH-Px and ?-GCS in serum for 60 th,90th and 120 th days(P>0.05).(3)The relative expressions of CAT mRNA in 400 and 750 mg/kg L-carnitine groups,CuZn-SOD mRNA in 750 mg/kg L-carnitine group,GSH-Px mRNA in 750 and 1100 mg/kg L-carnitine groups significantly up-regulated at the 60 th days(P>0.05).The relative expressions of CAT mRNA in 50,400 and 750 mg/kg L-carnitine groups,CuZn-SOD mRNA in all period,GSH-Px mRNA in 400 and 750 mg/kg L-carnitine groups significantly up-regulated at the 120 th days(P>0.05).Compared with the control group,the relative expressions of Nrf2 mRNA in 400 and 750 mg/kg L-carnitine groups significantly up-regulated,and Keap1 mRNA in 400,750 and1100 mg/kg L-carnitine groups significantly down-regulated at the 60 th days(P>0.05).The relative expressions of Nrf2 mRNA in 400 and 750 mg/kg L-carnitine groups significantly up-regulated,and Keap1 mRNA in 50,400,750 and1100 mg/kg L-carnitine groups significantly down-regulated at the 120 th days(P>0.05).In conclusion,the results showed that the addition of L-carnitine in the feed could promote the growth and enhance the utilization of feed.It has a positive effect on the antioxidant enzyme system and non-enzyme system of Phoxinus lagowskii Dybowski.At the same time,L-carnitine can adjust the level of body's antioxidant system,up-regulation the expression of nuclear transcription factor Nrf2 mRNA while inhibiting the expression of Keap1 mRNA.There was a slight difference between the addition levels of L-carnitine,and the optimum dosage of L-carnitine was 530 mg/kg under the premise of minimizing the production cost.