Effects Of Ammonia Nitrogen Stress On Related Organs And Immune Factors Of Micropterus Salmoides

Ammonia nitrogen?N?is a major source of water aquaculture and a cause of fish diseases.The acute toxicity experiment of ammonia-N to juvenile Macropterus salmoides in weight?19.70±1.98?g was carried out in static water without feeding at water temperature21.0?,pH 7.9,and dissolved oxygen 8.0 mg/L.This study was first exposed to total ammonia-N for 96 h to obtain the median lethal concentration(LC₅₀)at 96 h.According to the data,we set up a control group and three ammonia-N treatments of which the concentration were low group?19 mg/L?,middle group?28.5 mg/L?,and high group?38mg/L?.In each group the subjects were treated for a series of periods?0,6,12,24,48,72 and96 h?.The acid phosphatase?ACP?and catalase?CAT?activity and the malondialdehyde?MDA?content of the gill,liver,intestine,kidney and brain were measured.The results obtained were as followed.The LC₅₀ of total ammonia-N on juvenile at 96 h were 63.34 mg/L.The LC₅₀ of non-ionized ammonia on juvenile at 96 h were 2.05 mg/L.The safe concentration of total ammonia-N and non-ionized ammonia was 6.33 and 0.21 mg/L.After 96 h treatment with ammonia-N,the ACP and CAT?except the intestine?activity and the MDA content showed a trend of increasing first and then decreasing with prolonged exposure,which was significantly different from the control group?P<0.05?.The content of MDA?except for 48 h in the kidney?accumulated to the maximum at 12 h,and gradually decreased with the further activation of enzymes such as CAT.Under acute ammonia-N stress,CAT reached the highest level at 6-12 h and ACP reached the highest level at 24-48 h,and then gradually decreased.Compared with the control group,the MDA content in the 38 mg/L concentration group was significantly increased at 96 h?P<0.05?,and the removal trend was significantly slowed.The ACP and CAT activity in the 28.5 mg/L and 38 mg/L concentration group were significantly higher and lower than t the control group?P<0.05?,respectively.This study revealed that some of the cell functions were damaged,especially the CAT activity in the intestine in each concentration group was significantly lower than the control group?P<0.05?,and there was no recovery trend.At this time,the cell function was severely inhibited.Although the 96 h LC₅₀ of total ammonia-N on juvenile Macropterus salmoides was 63.34 mg/L,when the ammonia-N concentration was 28.5 mg/L,the cell function in some tissues was damaged after96 h treatment.The safe concentration of non-ionized ammonia was 0.21 mg/L.The results suggested that Macropterus salmoides had strong tolerance to ammonia-N.The CAT activity in the gill and intestine and the ACP activity in the gill can accurately reflect the degree of oxidative damage,and can be used as a marker to evaluate the toxicity of ammonia-N in aquaculture water.Samples of three-tailed fish were collected at 0,24,48,96h and 7d after stress.Under ice bath conditions,the body was dissected,and the gill filaments on the second gill arch on both sides of each test fish were quickly used for liver and kidney in the same part.Rinse with normal saline,absorb water with filter paper,fix with Bouin solution,dehydrate with ethanol at different levels,embed sections with conventional paraffin,5?m thick,H.E stained,observe with microscope and take pictures.Under long-term ammonia nitrogen stress,the gills of largemouth bass become thicker,shorter,fused,and disappear,which seriously affects the respiratory function of the fish.The degree of kidney damage increases with time,and there is extensive necrosis of the glomeruli and tubules,affecting the excretory function of the fish.Hepatocellular vacuolation and necrosis impair its metabolism and detoxification function.The damage of gill,liver and kidney tissues of largemouth bass after ammonia nitrogen stress is obvious,which shows that the severity of damage caused by ammonia nitrogen stress can be seen by observing the slices of gill and liver.Attention should be paid to the monitoring and management of water quality during the breeding process to prevent the toxic effects of ammonia nitrogen on juvenile largemouth bass.