Physiological Response To Stress Of Ammonia And Nitrite In Tilapia, Oreochromis Niloticus

Tilapia is the largest export-oriented fish in southern China,in the process of high density raising often faced the stress of ammonia and nitrite in aquaculture water.The change of ammonia and nitrite stress related physiological and biochemical indexes of tilapia was studied,a preliminary discussion on the physiological response of ammonia and nitrite stress of tilapia.1.In order to study the effect of acute toxicity of ammonia of Nile tilapia,setting 7 ammonia concentration gradient group in accordance with the logarithmic spacing.The study found that the 96h LC50 for Nile tilapia was 139.7 mg/L.Nile tilapia under the high ammonia concentration stress poisoning symptoms,with increasing ammonia concentration,mortality increased rapidly,and even all death.The survival rate of juvenile niloticus showed a negative correlation with ammonia concentration and the time of poisoning.As the research object,the initial body mass of the Nile tilapia(Oreochromis niloticus)was(21.25 ± 0.11)g.Setting control group(A0)and four experimental groups,the experimental group of ammonia concentration were 3.49 mg/L(A1),6.99 mg/L(A2),13.97 mg/L(A3),27.94 mg/L(A4).After Satiation fed 30d,mensurated the growth,blood routine parameters and enzymatic activity of fish under ammonia stress.Under chronic ammonia stress,surface mucus of Nile tilapia were increased,swimming slowly,the rays were defected and the pectoral fin base be congested,some dead individuals tail fester,gill hyperemia,intestinal food rarely,white liver,especially in the A4 treatment group(27.94 mg/L).The results showed that Nile tilapia growth rate(WGR)and specific growth rate(SGR)decreased with the increasing of the concentrations of ammonia nitrogen,the number of white cells in each group were significantly higher than those of the control group(P<0.05,hereinafter the same),hemoglobin was significantly lower(by 8.98%～15.50%),hematocrit than the control group also has fall(by 5.80%-12.06%).After 30 d stress,the activity of serum AKP of A4 group was significantly lower than the control;The activity of SOD in A2,A3 and A4 treatment groups were significantly lower than the control.Serum triglyceride and cholesterol concentrations of A4 group were significantly lower than those in the control;The activity of ALT and AST in serum of the A3 and A4 treatment group was significantly lower than that in the control.Acid phosphatase and alkaline phosphatase activity in tilapia liver showed a rising trend,superoxide dismutase and alanine aminotransferase were significantly lower than those of control.The research showed that growth,blood routine parameters and liver enzyme activity of Nile tilapia were influenced under chronic ammonia stress.Immunity,anti stress ability and disease resistant ability of fish were decreased.In practice,we should pay close attention to ammonia changes in aquaculture production in order to reduce stress on the fish immune function of the ammonia effect.2.In order to know the effect of nitrite stress on physiological function of juvenile Nile tilapia(Oreochromis niloticus),the research on the response of blood routine parameters and related biochemical indexes in serum under the stress of different concentrations of nitrite(control,1 mg/L,2 mg/L,4 mg/L and 8 mg/L)were carried out.The results showed that the trend of change in the number of leukocytes in blood showing increased first and then decreased,red blood cell,hemoglobin and hematocrit showed decreased with nitrite concentration increased.After 7d sress,with increase of nitrite concentration,serum Na+ and Cl-in Nile tilapia showed a downward trend,of which 4 and 8 mg/L experimental group Na+ and Cl-were significantly lower than those of the control group(P<0.05),the serum content of K+ in the experimental group were significantly higher than those in the control group(P<0.05);Serum superoxide dismutase,alkaline phosphatase,total protein,cholesterol and triglycerides of Nile tilapia showed a decreasing trend,superoxide dismutase,alkaline phosphatase and total protein of the 4 and 8 mg/L experimental group were significantly lower than those of the control group(P<0.05),serum alanine aminotransferase,aspartate aminotransferase,lactate dehydrogenase and glucose levels showed a rising trend with the increase of nitrite concentration.The research showed that blood routine parameters and serum biochemical indexes of Nile tilapia were influenced under short-term nitrite stress.Immunity and anti stress ability of fish were decreased.In practice,we should pay close attention to nitrite changes in aquaculture production in order to reduce nitrite stress on physiological function of fish.