Effects Of Melaleuca Alternifolia Essential Oil On Growth,Immunity And Resistance To Ammonia Nitrogen Stress In Macrobrachium Rosenbergii

Macrobrachium rosenbergiih is freshwater shrimp breeding species in China.During the breeding of M.shrimps often suffer from diseases such as black spot disease and muscle whitening and necrosis due to the influence of water temperature and water quality.For prevention,we often use antibiotics to improve the disease resistance of shrimp.But antibiotics have adverse effects on shrimp,and remain in the shrimp and ultimately affect human health.So,finding a healthy and harmless M.immunopotentiator is importantIn this experiment,tea tree oil,a non-toxic and harmless plant extract,was used as an immunopotentiator in the feed,and it was evaluated from the aspects of growth performance,antioxidant,non-specific immunity.To investigate the optimum level of tea tree oil as an immunopotentiator for M.rosenbergii and its ability to respond to ammonia nitrogen,and to explore the effects of different feeding modes on M.rosenbergii.The experiment included three parts:Experiment 1:Effects of different levels of tea tree oil on growth,antioxidant capacity and blood biochemical of M. rosenbergiiThe experimental M.(0.39±0.01 g) was randomly divided into 6 groups with 3 replications in each group,and 50 shrimps in each group were randomly placed in 18 cement tanks (2.0×1.5×0.5m).The experiment was divided into 6 groups,respectively added 0,25,50,100,200 and 400 mg/kg tea tree oil.The shrimp were fed 3 times each days,the feeding amount is 5% of shrimp body weight,and the breeding period is 8 weeks.After feeding trial,record the shrimp were weighed in each cement tank and hemolymph was collected.The results showed that:(1) The weight gain rate and specific growth rate of M.rosenbergii in the 100 mg/kg and 200 mg/kg tea tree oil groups were significantly increased(P<0.05),and the bait coefficient in the 200 mg/kg tea tree oil group was significantly reduced (P<0.05).The survival rate of the 100 mg/kg tea tree oil group was significantly improved (P<0.05).(2) The 100 mg/kg tea tree oil group added to the diet significantly reduced the levels of AST andALT in hemolymph (P<0.05),and increased TP and ALB levels.(3) The MDA content of each experimental group was significantly lower than that of the control group,and the superoxide dismutase (SOD) vitality of 25t o 100 mg/kg tea tree oil group was significantly increased (P<0,05).(4) The Nitric oxide (NO) and inducible nitric oxide synthase (iNOS) levels were increased with 100 mg/kg tea tree oil group,had significant difference from the control group (P<0.05).The results show that the addition of tea tree essential oil to the feed can improve the growth performance,antioxidant and nonspecific immunity of M.rosenbergii,and the 100 mg/kg tea tree essential oil group has the best effect.Experiment 2:Effect of TTO supplement on resistance of M.rosenbergii to ammonia nitrogen stress.After the end of the experiment,the shrimp were fasted for 24 hours.Select 20 shrimps in each tea tree oil level group and put them in the prepared bucket.Slowly add ammonium chloride until the concentration reached 20 mg/L.Then started ammonia nitrogen stress for 24 hours,after stress sampled the shrimp’s hemolymph and intestines.The results showed that CREA content in the tea tree oil group with 50 mg/kg added after ammonia nitrogen stress was significantly lower than that before ammonia nitrogen stress (P<0.05),and the levels of AST and ALT were significantly reduced compare with before stress (P<0.05),the levels of TP and ALB were significantly reduced compare with before stress (P<0.05).Compared with pre-stress,SOD activity of tea tree oil group with addition of 50 to 400 mg/kg was significantly increased after stress (P<0.05),MDA content of each group was not significantly changed after stress except that of the 400 mg/kg group (P>0.05),and MDA content of the 400 mg/kg group was significantly higher than that before stress (P<0.05).After stress,there was no significant difference in antioxidant anion content among the groups (P>0.05).After stress,NO content in group added with 50 mg/kg tea tree oil was significantly higher than that before stress (P<0.05),and iNOS content in each group was significantly higher than that before stress (P<0.05).After stress,the respiratory burst activity of added with 100 mg/kg tea tree oil group was significantly higher than that before stress(P<0.05).The expression of 50,100 and 200 mg/kgperoxiredoxin-5 genes was significantly reduced after ammonia stress (P<0.05).To sum up,feed added with proper concentration of tea tree oil has a significant anti-ammonia nitrogen stress effect on M.rosenbergii.The group added with 50 mg/kg tea tree oil had the best effect,added with 100 mg/kg tea tree oil group second best effect.Experiment 3:Effect of TTO feeding patterns on growth and non-specific immunity of M.rosenbergiiThe feed and breeding conditions used in the experiment were the same as in experiment 1.The experiment is divided into 4 feeding patterns,P1:fed the basic feed all the way;P2:fed the basic feed and the feed supplemented with 100 mg/kg tea tree oil at intervals of one week;P3:fed the basic feed and the feed supplemented with 100 mg/kg tea tree oil at intervals of one week;P4:the whole course was fed with the feed supplemented with 100 mg/kg tea tree oil.Shrimp hemolymph and intestines were collected after feeding trial.The results showed that the weight gain rate and specific growth rate of M.rosenbergii in the P3 and P4 groups were significantly higher than those in the P1 group (P<0.05),and there was no significant difference in survival rate (P>0.05).The content of NO and iNOS in the experimental group were significantly higher than that in the P1 group,and the content of MDA was significantly lower than that in the P1 group (P<0.05).The SOD activity of P3 and P4 groups was significantly higher than that of P1 group (P<0.05).In addition,the height and width of intestinal villi in P3 group were significantly higher than those in P1 group(P<0.05),and compared with the control group,the intestinal TNF-α,IL-1,Toll,Dorsal,and gene levels were significantly reduced (P<0.05) The expression of Peroxiredoxin-5 gene in P3 group was significantly higher than that in other groups (P<0.05).In summary,the addition of tea tree oil to the feed can improve the immunity and growth performance of M.rosenbergii.The use of 100 mg/kg tea tree oil fed at intervals of two week can improved the intestinal immune function of M.rosenbergii and the growth performance of shrimp,the antioxidant effect was also the best.