Recently, Pelteobagrus fulvidraco has a high incidence in the whole country, and the outbreak is fierce. Some people even wiped out the entire pond, causing a direct economic loss of two to three million yuan. According to statistics, the most severely affected areas are concentrated in Hubei and Jiangxi. Some farmers reported that small melon worms appeared in 9 out of 10 ponds in the surrounding fish ponds, and Guangdong, Guangxi, Hunan, Sichuan and Zhejiang have also gradually entered. The high incidence period of melon pests.
It is understood that the large-scale death of yellow catfish in Central China and Jiangsu and Zhejiang at the beginning of this year is directly related to small melon worms. Why is it so hard to get worms? Is there any way to prevent it? What should I do if I find that fish is infected by melon worm?
Fast onset, fast reproduction, high mortality
Freshwater fish suffer from it
Small melon worms belong to the multi-child melon worms in the ciliates. The body is round like a sphere. It can be said to be the "big worm" in the protozoa. It can even be seen with the naked eye. The worm has the characteristics of fast onset, fast reproduction, and high mortality. The water temperature is between 16℃-25℃, which is more suitable for its growth and reproduction. One small melon worm can produce 1024 small melon larvae through the second division in one night. , Most freshwater fish suffer from it.
In our aquatic products industry, many people think that the melon worm, like cancer, is difficult to treat. This is related to the special life history and morphological structure of the melon worm. There are three stages of the life of the melon worm. There is no need for middle Host.
—— | Nourishment period | ——
After the larva of the melon worm enters the skin or gills of the fish, the worm grows into an adult and leaves the fish body. This is the parasitic stage. The body of the worm can divide and reproduce, but generally after 3-4 divisions, it will no longer divide. At this time, it can be seen that the double-divided somatic cells of similar size are arranged in rows or clusters under the epithelial layer of the host. When the insects develop to this condition, it is difficult to kill them, because this kind of insects usually do not Will leave the host.
As a result, the fish is stimulated to secrete a large amount of sticky substance to surround the larvae, forming small white vesicles that are visible to the naked eye, that is, the small white dots that we mentioned earlier, but the larvae enclosed in the small vesicles can still use the fish. The tissue cells of the worm are used as nutrients to further develop into adult worms. Because the parasitic stage of the worm is protected by the protective layer formed by the host's secretion of sticky substances, it is difficult for the drug to penetrate. When it grows up as an adult, it often bursts out of its capsule and floats into the water.
—— | Encapsulation stage | ——
From the time when the adult worms detached from the fish body to form cysts to rupture. The parasitic melon worm leaves the fish body only after it matures, and after a period of free swimming (about 3-6 hours), it falls to the bottom of the water body to stop and secrete a layer of gelatinous membrane to enclose the worm body and form a cyst. The worms in the cysts divide and reproduce, and generally can hatch 500-1000 larvae at a time. Due to the cyst protection, the worms at this stage are not sensitive to drugs.
—— | Predator stage | ——
The larvae develop to a certain stage, break through the cyst, swim freely, and enter the stage of infecting the fish body, which is the predatory stage in the life history of the small melon worm. At this stage, there are abundant cilia growing around the body of the worm, which swims toward the body of the fish, relying on the piercing glands on the head to drill into the skin and gills of the host fish.
The small vesicles seen before are formed on the skin or gills of the fish, completing a life cycle. The infectivity is strong within 24 hours after incubation, and the infectivity gradually decreases over time. This period is a drug-sensitive period. If the host fish is not found within 1-2 days, the larvae will die by themselves.
Prevention and control must improve fish immunity
Water cultivation, insect repellent, antibacterial
Melonworm disease is prevalent all over the country. It is not selective to the host. It not only likes to parasitize on yellowbone fish and catfish, but also various freshwater fish, migratory fish, and ornamental fish. This disease is more likely to occur in small water bodies that are not flowing and high-density farming, and the water quality is deteriorating; fish of all age groups from fry to adult have parasites, but the fish species are mainly endangered.
Most freshwater fishes are deeply affected by melon worms. The most effective way to prevent melon worms is to prevent them in advance. Firstly, it is simple and convenient, and secondly, the cost of medicine will be greatly reduced.
Knowing the weakness of the small melon worm in the reproduction stage, we must take effective control against this:
1. Thoroughly clear the pond. Before stocking fingerlings, use quicklime to thoroughly clear the breeding pond.
2. Increase the water temperature of the breeding water body. Under the conditions of pond culture, prevention can be implemented by appropriately lowering the water level to increase the water temperature in the late autumn, early winter and early spring.
3. Improve the immunity and disease resistance of farmed fish. The physiological condition of fish is directly related to the occurrence of cucurbita vulgaris. The low immunity of fish is more susceptible to the invasion of Cucumber worm predators. Therefore, the nutrition of farmed fish should be strengthened during the epidemic season of melon worm disease. It is recommended to take "bile acid + electrolytic multi-dimensional" orally to improve the immune resistance of fish.
4. Improve water quality. The occurrence of melon worm disease is closely related to the water quality of the pond. The thinner the water quality, the more likely it is to break out of melon worms. Proper fertilization of water also helps to inhibit the growth of melon worms.
5. Pay attention to deworming and antibacterial. Deworming is not killing insects, but preventing small melon worms in the water from parasitizing the fish. In particular, non-scale fish are very sensitive to insecticides, and the use of insecticides will cause internal organ damage, thereby reducing the fish’s immunity. We also need to abandon the concept of regular insecticide in our breeding. We can choose safe and non-toxic plant extracts, such as Lechang Eucalyptus essential oil, which is extracted from the leaves of Eucalyptus multiflorum and has strong penetrating properties and can reach the insect body directly. , Inhibit the reproduction of small melon worms. At the same time, with sprinkling, it can inhibit the small melon worms in the water body, so that they can not parasitize the fish body smoothly. After the nutrients are exhausted, they will naturally die in the water.
â–¡The frontier of large California perch fish at Tangbian University
The life cycle of melon worm: ①vegetative body leaving the fish body; ② division within the cyst; ③ larva formation; ④ released larva; ⑤ parasitic.
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