What should I do about the problem of small melon worms after "light snow"?

After the snow festival, the temperature continues to drop, but the weather is not too cold, and the disease of farmed fish is reduced, but aquaculture must also pay attention to the occurrence of small melon worms.

The genus is a genus of protozoa phylum, ciliates, notchs, and melons, and is an obligate parasite.

Epidemic situation: the hazard object is not selective, all kinds of sea and fresh water have occurred; the epidemic area is wide, all parts of the country are occurring; the suitable water temperature for breeding is 15-25 ° C, which is popular in early winter and late spring, and does not occur when the water temperature is lower than 10 ° C or higher than 26 ° C. Transmission by sporangia and larvae. Newly hatched larvae are highly invasive and gradually weaken over time.

Symptoms: Mainly parasitic on the skin, fins, gills, head, mouth and eyes of fish, forming a small white dot shape of the sac, which is visible to the naked eye. In severe cases, small white spots can be seen all over the body of the fish, so it is called white spot disease. Fragments of gills are deformed, capillaries are hyperemia, exudation, ischemia, swelling and necrosis of respiratory epithelial cells.

Fish infected with small melon worms can not forage, coupled with secondary bacterial and viral infections, can cause a large number of fish deaths, or even the entire army, posing a serious threat to aquaculture production.

Adult stage: adult ovoid or spherical, visible to the naked eye; soft body, densely covered with short and uniform cilia, the cell mouth is located on the ventral surface of the front of the body, the cilia of the perigus are composed of 5-8 rows of cilia, rotating in the opposite direction of the clock, all the way to the pharynx; the large nucleus is horseshoe-shaped or sausage-shaped, the small nucleus is round, close to the large nucleus, there are many small telescopic vesicles in the outer layer of the cytoplasm, and the endoplasm is composed of a large number of food particles.

Larval stage: the body is ovate or oval, pointed at the anterior end, and blunt in the posterior end. There is a papillary drill at the front. The whole body is covered with equal-length cilia. At the rear end there are 1 long and thick tail hair. The large nucleus is oval or ovate. There is a large telescopic vesicle at the front of the body, the "6" shape of the original cell mouth has not yet passed the same as the interior, and there is an oval reflective body at the notch of the "6" shape, which may be related to the formation of the cytopharynx in the future. This stage is the infection period of the small melon worm.

Encapsulation period: the insect body that leaves the fish body or the insect body that crosses the vesicle can swim for 3-6 hours and then sink into the object at the bottom of the water. After resting, a thick gelatinous film is secreted to envelop the insect body, that is, the capsule. That is, the period from the time when the melon worm breaks away from the fish body to form a cyst to the time when the cyst ruptures. The capsule is round or oval, white and transparent.

The orifice of the worm body in the cyst disappears, and the large horseshoe-shaped nucleus becomes round or oval, and the small nucleus is visible. The body of the sac is active and begins to divide after 2-3 hours. The division is repeated continuously until there are 300-500 larvae in the sac. It is usually aliquoted when divided, but after 32 worm bodies, 2-3 clumps of ciliary larvae of different sizes often form in the sac. Ciliated larvae go beyond the cyst and infect the fish. The larvae burrow into the epithelial cell layer or intergill tissue on the surface of the body, stimulating the proliferation of surrounding epithelial cells, thereby forming small vesicles. In it it develops into an adult worm, leaves the host, and forms a cyst.

At present, there is no very ideal drug for the prevention and treatment of small melon worm disease, and the principle of prevention over treatment must be observed. Excess silt at the bottom of the pond is removed, and the cement pool wall is washed and disinfected with quicklime or bleaching powder. For ponds and nursery waters, increase the amount of water exchange, improve water quality, and regularly use "Hanbao Blue" for disinfection. Nursery room utensils are frequently disinfected and dedicated to the pool. A sampling examination should be carried out before the fish descend the pond or enter the cage, and if small melon worms are found, they should be treated in time. The stocking density should not be too large, and the nutrition should be strengthened daily to improve the resistance of the fish body. When designing and producing cage fishing rows, their distribution should be reasonably planned and laid out, and the density should be appropriate. Usually, the cage setting area can be adjusted once a month, and the aquaculture cage can be brushed frequently to keep the cage water flowing smoothly. Regular sterilization and disinfection with Akojing is used to ensure that the water quality of the water body in the breeding area is good. When the melon worm is infected, you can use paprika and ginger to use a dose of 0.8g and 1.5g per cubic meter of water, add water to boil for 30 minutes and then sprinkle the whole pool, once a day, for 3 to 4 days; or use Materia Medica, water worm net, etc. to sprinkle the whole pool during the epidemic season.

In addition, through the understanding of the life history of small melon insects, it can be known that small melon insects have a thick layer of host protection in the parasitic stage, so the small melon insects at this stage are not sensitive to drugs, and only those melon insects that are basically mature, about to leave the fish body or just detached are sensitive to drugs. Therefore, when using drugs, it is necessary to use a certain course of treatment continuously, generally 2-3 courses of treatment, in order to completely kill the insect body, and the specific length of the interval between the courses depends on the breeding conditions. Either the temperature rises or decreases are favorable factors for controlling the condition. Small melon worms are very sensitive to external osmotic pressure, so make good use of this feature. Using table salt to stimulate the small melon insects to leave the body and then kill the isolated small melon insects is also a very good treatment.