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Fish ringworm disease is one of the main parasitic diseases that are very seriously harmful to bulk freshwater fish, and the life history of ringworms is simple, the life cycle is short, and the reproduction rate is very fast, so it is easy to form epidemic outbreaks. Ringworms are hermaphrodites. There is an ovary in the posterior part of the worm body, and the sperm nest is behind the ovary. Ringworms are widely distributed, endemic in summer and autumn, and diseased fish can often have more than 60 insect bodies on a gill piece. Ringworm disease has a high incidence at the seed stage and is quite lethal to young fish, but it is not harmful to healthy adults.
Ringworm disease is more difficult to prevent, but it is not impossible, such as thorough pond clearance in spring and winter, soaking fish bodies with drugs such as enemy insects before stocking fish species, etc., which can greatly reduce the possibility of ringworm disease. In fact, the outbreak of ringworm disease has a lot to do with the density of culture, and when it is found that a large number of ringworms are parasitic in the field survey, it will not occur, reducing the density of culture can effectively prevent the outbreak of ringworm disease. In addition, try not to buy seedlings in endemic areas and avoid bringing pathogens into ponds. However, the above methods seem to be less willing to be done by farmers now, preferring to directly pour medicine in the pond to prevent it.
Fish suffering from ringworm disease symptoms and pathological changes and hazards
Fish severely infected with ringworms have black body color, thinness, slow swimming, loss of appetite, increased gill mucus, lighter gill petals, and difficulty breathing; fry with severe disease will have swelling of the gills and difficulty closing of the gills.
The harm of ringworm disease to fish is mainly manifested in the following four aspects
1) The fixation of ringworms in the gills of the fish body will destroy the epidermal cells of the gills, causing the stress response of the fish body, resulting in abnormal action and loss of appetite;
2) Stimulate gill cells to secrete too much mucus, hinder the breathing of fish, and cause suffocation and death of fish;
3) Some ringworms feed on the blood of fish, and its large amount of blood sucking and the blood loss caused by its damage to gill tissue will cause anemia in the fish;
4) It is also very important that the damage caused by ringworms in the gills of the fish body can cause secondary infection of other pathogens (especially bacteria), causing more serious harm to the fish body.
Medication modalities for the control of ringworm disease
Many parasitic diseases, including ringworms, have been found to be increasingly refractory over the years, which may be related to blind medication leading to insect resistance.
In the process of medication, we should pay attention to four points:
1) Do not use drugs regularly, so as not to cause drug resistance of ringworms, especially not to stimulate ringworms with low concentrations of drugs on a regular basis.
2) Do not see insects and take medicine. A small number of ringworm parasitism in fish is a very normal phenomenon, even in excellent natural water bodies will exist, which will not pose a hazard to the normal growth of fish, but at this time to strengthen the management of pond water quality, pay close attention to changes in the number of ringworms.
3) Timely medication should be taken. Nowadays, insecticides are almost all effective for ringworm larvae, so when a large number of smaller ringworms are found on the gills of fish, they must be killed in time, and the concentration of medication must be accurate, and the amount of medication cannot be reduced at will; if the gills of the fish are found to be larger mature ringworms (pregnant eggs), it is necessary to use the drug again after the initial medication for a week to kill the next generation of larvae, because many drugs have no effect on the eggs.
In addition, when contiguous fish ponds are in outbreaks of ring worm disease at the same time, they should be medicated at the same time to avoid secondary onset due to water exchange.
Whether it is prevention or treatment, the currently used drugs are mebendazole and dimethodium, the effect is not bad, the concentration can be used according to the product instructions, special attention can not be reduced, the concentration must be accurate. In fact, as long as scientific drugs are used, many drugs have a good effect on ring worm disease, but prohibited drugs must not be used.
Correct identification of pathogens and statistics on their parasitic intensity
Correct identification of pathogens is an important basis for diagnosing fish parasitic diseases and taking corresponding measures, and the diagnosis of ringworm diseases is rapid and effective. Rapid diagnosis of ringworm disease is relatively easy depending on its form, number and symptoms.
The individual of the ringworm is small, retractable like an ant, has two pairs of tan eye spots arranged in a square arrangement on the head, and a large disc-shaped fixator at the back of the worm body, a pair of anchor-shaped central hooks and seven pairs of small edge hooks. However, these characteristics can only be observed under a microscope or dissecting mirror, and large farms should be equipped with a microscope or dissecting mirror, and those who do not have the conditions should be sent to the relevant clinic or laboratory to confirm the diagnosis.
In the gills of the sick fish that are severely infected with ringworms, the ringworms gather in swarms, and the gray-white insect body on the gills can be seen with the naked eye. These insect bodies are gently removed with forceps and placed in small utensils filled with water, and individuals who squirm like ants can be seen, that is, basically can be diagnosed as ringworm disease.
If the infection is not very serious, it is impossible to see the gills with the naked eye, so it is necessary to remove the gills, separate the gills piece by piece, put them on a glass slide, drop a few drops of water, examine them piece by piece under the autopsyoscope, and see that if the fish body shows the symptoms described above, and can see more insects through the naked eye or microscope, it can be diagnosed as ringworm disease; but sometimes the symptoms are not obvious, in this case, as long as a large number of insect bodies (especially larvae) are observed, it can also be diagnosed as ringworm disease.
Treatment of fish ringworm disease
1. The whole tank is sprinkled with mebendazole, the dose is 15 grams per acre per meter water depth, and no new water is added within 72 hours after taking the drug.
2. When the water temperature is 20 ~ 30 ° C, sprinkle the whole pond with 90% crystal enemy insects, and the drug per cubic meter of pool water is 0.5 ~ 1.0 grams, and the effect is better.
3. Each cubic meter of pond water is sprinkled with 1 to 2 grams of dichlorvos powder containing 2.5%.
4. Sprinkle the whole pool with the mixture of dimethods and surface alkali, the ratio of crystalline insects to surface alkali is 1:0.6, and the mixture of each cubic meter of pool water is 0.1 to 0.24 grams.
5. Wash the diseased fish with 20 mg/L quinine hydrochloride solution.
6. Insecticides for other fish.
(Author: Wang Guitang, Researcher, Institute of Hydrobiology, Chinese Academy of Sciences, Doctoral Supervisor.) This article is the content of the interview report of the "Agricultural Treasure Book")
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