Grass carp disease control technology
Lei Xiaozhong
1. Grass carp hemorrhagic disease
1. Pathogen: A grass carp reovirus.
2. Symptoms and lesions: the body color of the diseased fish is dark and reddish, and the small fish species can be seen under the sun or light, which can be seen under the skin congestion and redness. The mouth, orbit, the top of the head, the lower jaw, the gill cap, the base of the fins are congested, and even the eyeballs are protruding. The skin of the diseased fish is stripped away, and the muscles show punctate or lumpy congestion, and in severe cases, the muscles of the whole body are bright red. Severely bleeding sick fish may have "white gills" or spotted hyperemia, but some sick fish have no obvious gill flaps. Some diseased fish make the whole intestine or local intestine bright red due to bleeding, but the intestinal mucosal layer is not decayed, and the intestinal wall is elastic. The types of symptoms can be roughly divided into "red muscle" type, "red fin red gill cover" type, "enteritis" type, these three types sometimes appear at the same time, sometimes only one type.
3. Epidemic situation: This disease mainly endangers grass carp summer flowers and fish species of the year. The epidemic season is from June to September, with July common in high-density, monoculture grass carp ponds and August in large-sized fingerling ponds for rare culture.
4. Prevention and treatment methods: The treatment of this disease is more difficult, so prevention is the mainstay.
(1) Before the arrival of the onset season, inactivated vaccines are injected for immunization and prevention, and the immunization period can reach 14 months.
(2) During the breeding period, the whole pond is poured with sodium dichloroisocyanurate 0.3 g/m3 or bleaching powder 1g/m3 every half month.
(3) Oral administration of rhubarb powder, calculated according to 0.5-1.0kg per mu of fish body, mixed into feed or made into pellet feed, once a day, continuous serving for 3-5 days.
2. Bacterial gill rot disease (aconitum plague)
1. Pathogen: a columnar flexus.
2. Symptoms and lesions: the gill filament of the diseased fish rots, the cartilage at the end of the gill filament is exposed, often attached to the "sludge", the inner epidermis of the gill cap is hyperemic, inflamed and decayed, and the middle is often corroded into a round or irregular transparent window, commonly known as "open skylight". Sick fish swim alone, the body color is black, especially the head is the most serious, known as "aconitum plague".
3. Epidemic situation: This disease mainly harms grass carp and blue fish, which is currently one of the most common and harmful diseases of grass carp and blue fish in China, and can be infected from fish species to adult fish. The water temperature is above 20 °C, the most prevalent is 28-35 °C, the epidemic period is From April to October every year, and july to September is the most prevalent season. It is often complicated with enteritis, red skin, and hemorrhagic disease.
4 Prevention and control methods:
(1) The fish pond is thoroughly disinfected with quicklime.
(2) During the onset season, 1g/m 3 bleaching powder or 0.2-0.3g/m3 strong chlorine can be sprinkled all over the pool.
(3) In the onset season, sprinkle 15-20g/m3 of quicklime every half a month to keep the pH of the pool water at about 8.
(4) Rhubarb ammonia extract, 1kg rhubarb plus 20kg 0.3% ammonia soaked for 12-24 hours and then sprinkled, the concentration is 2.5-3.7g/m3.
3. Bacterial enteritis (rotten intestinal plague)
1. Pathogen: Intestinal punctate aerogenous bacteria.
2. Symptoms and lesions: the abdomen of the sick fish is expanded, and there are often erythema and "moth fins" on both sides. The anus is red and swollen, purple-red, with yellow mucus flowing out of the abdomen under light pressure, hydrops in the abdominal cavity can be seen when the abdomen of the fish is cut open, and the intestinal wall is hyperemic and inflamed, red or purple-red, especially in the posterior intestine. The intestines are filled with yellow pus, commonly known as "rotten intestinal plague"; the liver is often red-spotted with bruised blood.
3. Epidemic situation: This disease is one of the most harmful diseases in China's grass carp and bluefish, with the most serious one-year-old grass carp, the epidemic season is 4-9 months, often manifested as two epidemic peaks: the incidence of grass carp above one year old is mostly in April-June, fishermen called "barley yellow"; grass carp species in that year are mostly in July-September, fishermen called "white dew heart". Mortality is extremely high after morbidity.
4. Prevention and control methods:
(1) Thoroughly clear the pond and disinfect, and strictly implement the "four eliminations" and "four determinations" methods.
(2) When the grass carp is ingested in the spring, the whole pond is sprinkled with quicklime 20-30g/m3 water, and combined with garlic bait for 3 days.
IV White-headed white-mouthed disease
1. Pathogen: a kind of myxococcus in fish pest.
2. Symptoms and lesions: the skin of the diseased fish from the end of the kiss to the eyeball is ulcerated, and the pigment around the forehead and mouth disappears, showing a milky white color. Due to the parasitism of a large number of bacteria, these parts are gray-white hairy, showing a white head and white mouth. When observed on the shore, the sick fish swim slowly on the surface of the water, and constantly "float their heads", sometimes exposing their heads to the water at a 45 ° angle, staying still, often showing explosive death.
3. Prevalence: This disease is the most common fulminant fish disease in the summer flower stage, and the fry in the lower pond can be affected for about 20 days. Rapid onset, short course of disease, high mortality, mainly harmful to freshwater farmed fish, especially to summer flower (2.5-3 cm) grass carp. It is endemic from late May to early July, with the peak period of incidence in June.
(1) The fish pond is cleared with quicklime to keep the water quality clean.
(2) Reasonable intensive culture, and the fry grow to 2-2.5cm in time to divide the pond.
(3) Sprinkle the whole pool with 1g/m 3 bleaching powder.
(4) Sprinkle with rhubarb ammonia leaching solution (the usage is the same as bacterial gill disease).