Although the disease in this farmed tilapia was only endangered by local outbreaks and did not form a pandemic hazard, it was the most serious disease hazard in the history of tilapia culture in Guangxi and it also sounded a warning for the tilapia breeding industry in Guangxi. .

August-November 2010, we were in Longan County, Wuming County, Xixiangtang District of Nanning City, Yuzhou District, Bobai County of Yulin City, Liubei District of Liuzhou City, Gangnan District of Guigang City, Hepu County of Beihai City An epidemiological investigation was conducted on the hazards of cultured tilapia in the district and samples were collected for laboratory testing. The results are as follows:

I. Disease Hazard Situation Since August 2010, farmed tilapia in Nanning and other places have experienced outbreaks of partial outbreaks, affecting 12 million mu of ponds and 20 in 16 counties in five cities of Nanning, Yulin, Guigang, Liuzhou and Beihai. Millions of m2 net cage culture tilapia caused a total of more than 30 million yuan in direct economic losses.

1. Epidemiological investigation found that the status of the tilapia disease is different.

Pond culture and cage culture have all had diseases, and the water quality is seriously endangered. In particular, pigs, ducks, chickens, or ponds that have been introduced into urban aquaculture are more harmful. Some of the farmer’s cultured tilapia died of disease. The rate is up to 100%.

For example, in Pang Weichang, Zhumei Street, Nanjiang Street Committee of Yulin District, Yulin City, 20,000 tilapia were reared on 26 mu ponds. On August 18, 2010, the fish began to develop. The drug treatment with conventional bacterial diseases was ineffective and the sick fish died every day. 60-300 tail, to the end of October all died of illness, dead fish 7000 kg; Nanzhou Street, Yuzhou District Changle Street, Cai Jian farmers, 20 acres of pond tilapia tilapia 18000, August 20, 2010 fish began to disease, Chlorine dioxide disinfection, oral administration of Yukangkangning + high-stability C, is ineffective, 150-300 dead fishes die each day, all died by the end of October, dead fish 9000 kilograms; Shangchang Long farmers in Hengxiang Nanxiang Town, Nanning City, In the 100-mu single-cultivated tilapia pond, 1.25 million tilapia seedlings were released on April 25. On August 23, the disease occurred. On August 25th, the sterilizer was disinfected with strong chlorine and fed with tilapia vaccine. Poorly, more than half died in mid-September, and by the beginning of October there was not much left.

2. The disease progression of tilapia varies.

Acute type, from the third day after the stocking began to disease, all died within two weeks; chronic type, from the onset of disease to the basic control of the disease took up to 4 months, the cumulative case fatality rate of up to 50%. Regardless of whether it is acute or chronic, the basic conditions are similar. The main manifestations are: sick fish swimming alone or in the water, mad swimming, loss of appetite or not feeding; fish body black, thin, eye convex or rotten eyes , Cover the lower edge, around the eyes, fin base and body surface congestion or hemorrhage, fins end rotting, abdominal distension, ascites; necropsy found adhesion of tendon, severe liver necrosis, hepatomegaly, intestinal congestion.

3. The pathogenic diversity of the tilapia disease.

Twenty-two batches of 14 sick fish or 14 ponds or cages were collected from 8 counties in Longan, Wuming, Xixiangtang, Yuzhou, Bobai, Liubei, Gangnan and Hepu. After isolation, agar plate purification, and API bacterial identification system identification, a total of sixty-three strains of bacteria were isolated from the liver, spleen and kidney of diseased fish, of which 19 were Aeromonas sobria, 21 Aeromonas hydrophila strains, and no milk chain. 7 strains of cocci, 1 strain of Pseudomonas fluorescens, 4 strains of Pseudomonas putida, 1 strain of Shigella spp. 1 strain; 14 ponds or cages, only 7 ponds or cages were single pathogens (mild Aeromonas hydrophila or Aeromonas hydrophila or Pseudomonas putida) hazard, 1 pond or cage is a common hazard to Pseudomonas fluorescens and Pseudomonas putida; 3 ponds are Aeromonas sobria And the Aeromonas hydrophila co-hazard, two ponds are the common harm of Aeromonas hydrophila and Streptococcus agalactiae, one pond is a common harm to Aeromonas sobria and Streptococcus agalactiae, and one pond is an addictive Aeromonas hydrophila and Pseudomonas genus Shigella common hazards. Moreover, different ponds in the same farm have different infections.

Second, the cause analysis 1, the epidemiological survey found that poor water quality of the pond and the cage is more harmful and higher mortality; necropsy found that the sick fish silk adhesion phenomenon is serious. This fully proves that the deterioration of cultured water quality is the main reason for this tilapia disease.

2. The necrosis and hepatomegaly of the diseased fish were found to be relatively serious in the necropsy. This indicates that the feed material used in the feed has a relatively high proportion of inferior raw materials, causing liver function decline and hepatic necrosis in the farmed fish. Severe decline in disease and infection.

3, medicine is not symptomatic, lack of medication, leading to the serious harm of this condition. The epidemiological investigation found that in the prevention and control of the disease, farmers have adopted different drug prevention and control measures, and the results are not satisfactory for two reasons: The first is that they do not understand the drug resistance of the local pathogens, leading to drugs. Not symptomatic, prevention and control of poor efficacy is a matter of course; the second is to disinfect the body of water with disinfectants, and then according to conventional bacterial disease prevention and control methods of internal medicine for 3 days, the efficacy of the drug is now beginning to stop, leading to repeated hazards of the disease.

4. Pathogenic bacteria such as Aeromonas hydrophila, Aeromonas sobria, Pseudomonas putida, and Streptococcus are widely found in aquaculture waters, and the disease resistance is reduced due to the deterioration of water quality and severe liver disease in farmed fishes. Under the circumstances, farmed fish can easily become infected with one or two of these pathogens.

III. Discussion and recommendations 1. Although the current disease status of tilapia farmed was only endangered by local outbreaks and did not form a large-scale epidemic hazard, it was the most serious disease hazard in the history of tilapia culture in Guangxi, and it was also the Luofei of Guangxi. The fish farming industry has sounded the alarm.

In the current situation where seed quality, aquaculture environment status, and feed quality are unlikely to be effectively improved in the short term, the potential hazards of farming diseases are extremely high.

2. The hazards of the tilapia disease in the farmed fish show that pigs, ducks, or urban sewage have poor water quality.

Therefore, to prevent and treat diseases, we must first do a good job in water quality management, adopt timely measures such as changing water and oxygen, and using biological agents to improve water quality, and maintain aquaculture water transparency of more than 20 cm and dissolved oxygen above 3 mg/l to prevent disease. occur.

3. The hazards of tilapia disease in farmed fishes also showed that the more severe the liver disease of farmed fish was, the higher the mortality rate was, indicating that the decline of feed quality would directly cause serious harm to the disease.

Therefore, scientific feeding of high-quality feed is one of the important measures for disease prevention and control. We choose to feed brand-name feeds with good reputation and stable quality, feed the feed at a daily feed rate of about 2.5% of the fish's body weight, and at the same time regularly feed the immune recovery agent such as vitamin C or Astragalus polysaccharide once a month on a regular basis. Feed 5-7 days continuously to increase the disease resistance of farmed fish and reduce the chance of disease occurrence and epidemics.

4. The long-term hazards of tilapia culture, poor treatment effect, and recurrent disease are common. They directly challenge conventional disease prevention concepts and technical measures. They also remind us that traditional timid prevention and control techniques are used to prevent and control today's farming. The disease is no longer enough.

It is necessary to collect samples in the early stage of the disease and send it to the laboratory for testing. According to the results of laboratory diagnosis and drug susceptibility testing, the sensitive national standard fishery drugs should be screened, and integrated prevention and treatment of integrated traditional Chinese and western medicines should be adopted, combined with water disinfection (once a day for three consecutive days). Oral administration of one kind of sensitive national standard fishery drug + one kind of traditional Chinese medicine with clearing away heat and detoxifying or protecting the liver and protecting the liver + astragalus polysaccharide or stabilizing vitamin C once a day and even feeding for 7 days can ensure the curative effect.