In continuous rainy days, the dissolved oxygen in the pool water was determined for many times not less than 9? Mg/L, eat normally. After that, it began to clear up. At 10 in the afternoon, about 10 sea bass swam, and the measured dissolved oxygen was 3.0mg/L, which was untreated. The next day, I found more than 200 tails dead, stopped feeding, and then died every day 10 days? 100~200, during which external use of formaldehyde and chlorine dioxide had no obvious effect. After taking the medicine, the water quality gradually became turbid. On the morning of 25th, the water was measured with a simple test box, and the ammonia nitrogen was 0.5? Mg/L, nitrite 0.6? Mg/L.? ? After 10, change the water by 50cm every day for 3 consecutive days. Will the future mortality rate drop to? 10~20 tails. 10 am arrived at the scene, and observed that the water color was improved and slightly turbid. The measured water temperature was 25℃, dissolved oxygen was still 3.0mg/L, ammonia nitrogen was absent, and nitrite was 0.4? Mg/L. Most diseased fish have no obvious abnormal symptoms. Some sick fish have stagnant water in their stomachs and intestines, and most sick fish have swollen and black spleens. Careful observation shows that there are white spots on the surface of spleen, liver and kidney.

Results of bacterial isolation and culture: A large number of bacteria can be isolated from liver, spleen and kidney, and the colonies are translucent and grayish white. 16S later? Edwardsiella tarda was identified by RDNA sequencing. Pathological sections showed that the liver was congested, the hepatocytes were concentrated, there were necrotic areas, and there was mild steatosis. There are many necrotic foci in the spleen, and the center of melanin macrophage can be seen. Renal congestion, hemorrhage, glomerular congestion, necrosis, sporadic necrosis of interstitial cells between kidneys.

? Analysis:? ? 1. The water quality in this case changed dramatically in sunny days after continuous rainy days, and a large number of deaths occurred in time after anoxic treatment at night, which also induced continuous deaths caused by Edwardsiella tarda. Because the water quality environment has not been completely improved, the therapeutic effect of oral antibiotics is poor. 2. Edwardsiella tarda grows slowly, forming small white necrotic foci on internal organs without obvious abnormal symptoms, which may be the characteristic symptom of Edwardsiella tarda in marine fish. Some perch water accumulation may be caused by lack of oxygen.