In 1984, China introduced spotted forktail catfish, after more than 20 years of breeding promotion, it has now developed to most provinces and cities in the country, and now Sichuan is also a large area of breeding spotted forktail catfish. Since 2015, affected by relevant foreign laws and policies, the processing and export volume of spotted forktail catfish has decreased year by year, so that the domestic market has gradually been developed, and the proportion of domestic sales has become larger and larger, so that the large-scale breeding of spotted forktail catfish, its market prospects are getting better and better, but there are diseases in the breeding process, especially after the winter every year. Disease is the most important factor in the harm to spotted catfish, causing significant losses every year. In February and March 2019, the temperature was relatively low, the temperature was slow, and the incidence of spotted forktail catfish in Sichuan was very high, the incidence exceeded that of 2018 and 2017, and the initial estimation of the incidence pond reached more than 10%! It has caused very large losses to farmers! Based on the results of the survey, we summarize it as follows:
<b>First, the epidemic situation</b>
In the spring of 2019, the author visited a large area of Sichuan where the explosive death of spotted forktail catfish appeared, through visits found that the explosive death of spotted forktail catfish appeared in Leshan, Renshou and other places in Sichuan Province, which was particularly serious, and most of them found that most of them did not know the cause of the disease during the communication with farmers, and at the same time learned that the spotted forktail catfish farmed in the fish pond were basically fish fry stocked last year and raised white silver carp, when the fish first became ill, the food was not good, the movement was slow, and several died every day. At their peak, thousands of deaths occur every day and the duration of the deaths is long. It shows high outbreaks, extremely high mortality, no therapeutic effect of conventional drugs, and zero cures. In terms of the outbreak of forktail catfish in recent years, the peak temperature of the disease is between 15 °C and 20 °C, and the mortality rate is very large. At the beginning of May, the disease began to decrease, and the mortality rate of the forktail catfish fell with it.
<b>Second, the main symptoms</b>
<b>During the visit, it was found that the spotted forktail catfish had the following symptoms:</b>
Initially sick fish with their heads up and tails facing down (Fig. 1); body surface ulcers or rounded fading spots with water mold attached (Figure 2); Bleeding at the gastrointestinal junction (Figure 3); Fry with rotten tails and fins (fig. 4); Intestinal purulent discharge, bleeding from the intestinal mucosa (Figure 5); Symptoms such as the intestinal bypass (Figure 6).
The disease mainly occurs in March and April of each year, small adult fish and large adult fish will be infected, but other species of hedge culture will not be infected, the diseased fish low water temperature lurking, the incidence of water temperature is mostly 15-20 degrees. In the early stages of the disease, the diseased fish will swim slowly, swim sideways or alone, lose or lose appetite, and die head up and tail down at the beginning of death, and finally sink into the water. The surface of the sick fish appears in a circle of faded spots, with blood streaks, and infected with water mold as the onset time of the disease is prolonged; Anatomically diseased fish found that there was no food in the gastrointestinal tract, the mucous membrane at the bottom of the stomach and the pylorus was congested and bleeding, the intestine was congested and bleeding, the intestine contained pus-like secretions, the intestines were spasmed, and the phenomenon of the intestinal bypass occurred in the hind intestine.
<b>3. Etiological analysis</b>
After communicating with the farmers, it was learned that the farmers initially treated the symptoms of the disease as water mold disease, appropriate subtraction, and found that it was ineffective, and water mold was a secondary infection after the onset of the disease. There is little research on the disease in China, and some people think that it is a columnar disease. However, after the common use of antibiotics and water disinfection, the effect is not very good, and the death rate increases. Hechen Technology Company began to study the disease in 2015, sent for testing many times, but did not isolate the bacteria, combined with epidemiology to deduce that it is most likely a virus.
<b>Fourth, countermeasures</b>
Our response plan is: start to do prevention work from November: 1, the water temperature is below 15 ° C, can not move the net, if you need to fish, please clear the pond. 2, the water temperature is lower than 22 °C, no insecticidal, no sterilization, reduce the stress on the fish body. 3. Start feeding immune feed. (Cellular immunity and humoral immunity of fish are enhanced by feeding immune feed in advance.) Improves the ability of white blood cells to swallow the source of the disease. It plays a role in fighting viral infections, reducing morbidity and reducing death. 4, control the water quality, ensure the dissolved oxygen in the water, try not to inject new water, pay attention to the change of algal phase, avoid changes in the water environment, and generate stress. 5, control the bait, can not be because of weather reasons and fish eat well and other reasons to increase feeding, try to gradually increase the amount after the water temperature and temperature rise and stabilize, reduce the intestinal load.
If death occurs: dead fish are first found: anti-stress products (fruit acid, VC, etc.) are sprinkled throughout the pond, mainly without insecticide and irritating disinfectants; a small amount of drugs or feeds that improve immunity can be fed; or feed can not be fed. If more than 100 fish/day/10 acres have died, the "three noes" + oxygenation policy is adopted. That is: no water change, no feeding, no medication, only oxygenation.
<b>5. Summarizing and summarizing</b>
The explosive death of spotted forktail catfish in early spring focuses on prevention and control, and the prevention and control of diseases is a systematic project, which cannot rely only on drugs, but also should control the environment externally to minimize stress. From the beginning of the fry, the spotted forktail catfish carries this pathogenic factor, but it is triggered under certain conditions, the triggers are different, the symptoms are also different, but enteritis, irregular fading spots are present in every diseased fish. In order to prevent the outbreak of diseases, water quality treatment and strengthen fish bodies should be taken precautions before winter, although the water quality changes slightly slower in winter than in spring and summer, but water quality also needs to be adjusted every month. In terms of feeding, due to the low water temperature, the overall feed amount cannot exceed 0.05%, or even not fed, and the feeding amount cannot be increased due to the sudden rise in temperature. (<b>This article is transferred from [</b><b>Hechen Technology</b><b>].) If you have copyright questions, please contact</b> [email protected]<b>. </b>）