Prevention and treatment of hemolytic ascites disease of bighead carp

With the gradual popularity of bighead carp in the market, most of the ponds in the suburbs of our city have changed from raising bighead carp to raising bighead carp. The yield of bighead carp has grown from dozens of jin per mu at the time of interculture to over 1000 jin per mu at the time of main culture. Due to the increase of bighead carp culture density, the incidence of bighead carp has also increased year by year, and the number of deaths has increased year after year, causing certain economic losses to farmers.

Hemolytic ascites disease of bighead carp is a fulminant infectious disease, also known as bacterial septicemia, which is caused by bacteria. Before death, most of the diseased fish roamed in the pond, the back was black, the mouth, jaws, operculum and eyes of the diseased fish were congested first, and the posterior fins and both sides of the fish showed mild hyperemia, and there was less food in the intestines. When you die, the body surface congestion increases, muscle congestion or bleeding is severe. When the disease is serious, there are many perforations at the base of pectoral fins, yellow fluid outflow, and most of them are right pectoral fins, exophthalmos are obvious, abdomen is dilated, anus is red and swollen, red mucus flows out of abdomen under light pressure, and the central endothelium of Gill cover bone corrodes and falls off, which seems to open a "skylight". The fish is thin and the skull is exposed. When dissecting the fish, yellow or red ascites could be seen in the abdominal cavity. The liver, spleen and kidney are enlarged and the tissue is very fragile. The color of liver and kidney becomes pale and anemic, the intestinal wall is congested and translucent, the intestine is inflated and contains dilute mucus, there is no food in the intestine, the Gill filaments are gray-white, anemia is serious, and the end is rotten.

I. time of onset and water temperature

The onset period of the disease is from early March to mid-November, and the water temperature occurs at 9: 36 ℃, especially when the water temperature is about 25: 35 ℃. The disease can be divided into acute type at high temperature (28-35 ℃) and chronic type at low temperature (3-5 fish per day in a 16-mu pond during the peak death period, but should be distinguished from the case of fish death during the cure period).

Second, etiological analysis

In the three fishing grounds investigated, the aquaculture area was 950mu in 2003, and the cumulative dead fish reached 16800 kg.

1. Pathogen: the main pathogen is Aeromonas aeruginosa, which is suitable for growth at 20-30 ℃, which is easy to cause fulminant epidemic.

two。 The disease mostly occurs in Laotang, where it has been cultured for a long time. The domestic sewage in the suburbs of our district has been raised by livestock manure for more than 20 years, so there is more silt in the ponds with serious disease, usually 10-20 cm, and some even up to 30-40 cm. The deep silt is an important factor in the outbreak of bacterial septicemia.

3. The density of pond culture is too large, and the stocking of bighead carp is more than 250 kg per mu, which is also one of the main reasons for the outbreak of the disease. Therefore, it is suggested that in the case of high-density culture, we must pay attention to adding new water, turn on oxygen-increasing equipment, and control the water quality.

4. The disinfection of fish fingerling before stocking is not complete, which leads to the introduction of bacteria and causes the disease. The mutual use of nets and tools and the littering of dead fish is also a major factor in the epidemic of the disease. Through investigation and analysis, if there is no cross-infection in the two adjacent fishing grounds, there will generally be no outbreak of disease.

5. During the period of high temperature in high-density culture, the number of gulls in the field increased, which led to mutual infection.

III. Corresponding measures

1. Precautionary measures

(1) if possible, remove too much silt from the pond and expose the bottom of the pond. Dry the pond with quicklime to clear the pond, and sprinkle it evenly in the whole pool with 50-70kg per mu. The clear pond with water is sprinkled with 125-150 kg quicklime in the whole pool with a water depth of 1 meter per mu. In the second year of the incidence of the pond in previous years, the amount of quicklime was increased by 100 kg per mu, and the whole pond was sprinkled with 20 g / m3 of bleach (containing 30% available chlorine 32%).

(2) do a good job of disinfection of fish before stocking. The stocking density of fish species should be reasonable, and it should be determined according to the water quality conditions and the technical level of the contractor, and it is generally appropriate to breed 50 kilograms per mu.

(3) Drug prophylaxis is carried out regularly. In the first half of the month, sprinkle 20g / m3 of quicklime in the whole pool, and in the second half of the month, you can sprinkle bleach (available chlorine 30%) 1 g / m3, or strong chlorine (84%) 0.3 g / m3.

(4) do not move the net in the sick pond. A large number of fish will die the day after the net is moved. In addition, when treating the disease, inorganic fertilizers such as ammonium bicarbonate can no longer be applied to improve the water quality, otherwise it will affect the curative effect and fail to achieve the purpose of cure.

two。 Treatment measures

(1) sprinkle with 1 g / m3 of bleach in the whole pool, or 0.3 g / m3 of strong chlorine in the whole pool, or 20g / m3 of quicklime in the whole pool. Quicklime, bleach or strong chlorine are used alternately once every half month.

(2) take enrofloxacin (20 mg / kg fish), norfloxacin (50 mg / kg fish) or rifampicin (10 mg / kg fish) once a day for 3 days.

(3) the water depth of 1 meter per mu is 1.5 kg of Guanzhong plus 50.7 kg of water, soak for 12 hours, then add 0.5 kg of alum and 30 kg of quicklime, and sprinkle it in the whole pool after dissolving water. At the same time, 5 parts of Huang Cen, 2.5 parts of Phellodendron Phellodendri and 2.5 parts of rhubarb were mixed with 8g / kg feed to make bait. During prevention, it was fed once a month for 2 days, and once a day during treatment for 6 days.