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Fish chylodonellosis

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DISEASES CAUSED BY INFUSORIESChylodonellosis - invasive disease of freshwater fish. Many aquarium, pond and commercial fish get sick.

The causative agent is a ciliator Chilodonella cyprini Clamidodontidae family, order Holotricha. The parasite is 45–70 µm long, 38–57 µm wide. The body is flattened in the dorsal-abdominal position, covered with cilia,

which serve as a vehicle for ciliates. On the ventral side, closer to the anterior end, is the mouth opening, from which a short pharynx departs, equipped with a rod chitinoid apparatus consisting of 18 sticks. There is a core in the middle of the body, and two contractile vacuoles closer to the edges.

Once on fish, chylodonella is localized on the surface of the skin, feeding on mucus and exfoliated epithelial cells. With the help of cilia, the parasite moves freely over the skin of the fish. In the same place, the ciliates multiply by dividing in half in the transverse direction.

Chylodonella mainly parasitize on the surface of the skin of the fish. Often there is a mixed form of chylodonellosis, when parasites are localized on the skin and gills. In adverse environmental conditions (changes in the hydrochemical regime, a sharp increase or decrease in the temperature of water, etc.), the ciliator forms a cyst. Cyst formation is accompanied by an increasing rotation of the parasite in one place, the speed of which reaches 30 rpm. After 1.5-2 hours from the beginning of cyst formation, contractile vacuoles increase, and the rate of their pulsation slows down. The cilia and rod apparatus of the pharynx disappear, the nucleus is rounded, the protoplasm acquires a pronounced granularity. By the end of the cyst formation process, the contractile vacuoles disappear, the rotational movements of the ciliates stop, and a double shell with a denser outer layer forms around it. The whole process of cyst formation lasts 3.5-4 hours.

Cysts are able to persist for a long time in the soil and in the water column. When the cyst enters favorable conditions for development, the cyst shell dissolves and an infusoria emerges from it, which attacks the fish and parasitizes on it. Bright, especially sunny, light prevents the reproduction of parasites, and vice also kills them.

In most literary sources, Ch. cyprini is described as a cold-loving infusoria that reproduces at a water temperature of 8–10 ° and dies at temperatures above 20 °. This is confirmed by the numerous cases of outbreaks of chylo-drnellosis of fish in pond farms precisely at the end of winter b early spring, when the water temperature in the ponds warms up to 8-10 °. Despite this, we cannot attribute Gh. cyprini is among the cold-loving ciliates, as they are parasitic on exotic fish, and the water temperature in aquariums is above 20 ° all year round. At the same time, one of the sources of the spread of chylodonellosis in aquarium fish farming is the ciliates brought into indoor water bodies from natural ones with live food, water, vegetation and soil. We found that Ch. cyprini taken from natural bodies of water, where the water temperature is 5-10 °, and placed in aquarium water (23-25 ​​°) are not able to cause the disease of exotic fish in the first 2-3 days, as they themselves “become ill”, adapting to new ones them to environmental conditions. At the same time, one should not forget about a sharp change not only in temperature, but in pH, hardness, oxidation of water and a number of other hydrochemical parameters, as well as a change in the hosts (fish) themselves. Once in new environmental conditions, one part of the ciliates dies, the second forms cysts (encysts), and the third, by the end of the third or fourth day, adapts not only to the high temperature of the water and the hydrochemical regime, but also goes on to parasitism, settling on new ones types of fish. Unfortunately, the fate of cystic ciliates has not been studied.

The correctness of the results of our studies is confirmed by the year-round parasitization of Ch. cyprini on aquarium fish at a water temperature of 22–27 ° C and cases of mass death of fish from chylodonellosis at these temperatures at different times of the year. The temperature optimums of growth and reproduction of chylodonella adapted on aquarium fish are currently unexplored.

Epizootology. Most aquarium fish of all age groups suffer from chylodonellosis, but fry and juveniles under puberty are more susceptible to disease.

Chylodonellosis can be described as a disease associated with dystrophy. As a rule, not only weakened, poorly fed fry and juvenile fish are sick, but also adults. Especially often chylodonellosis is observed in fish kept in poor conditions (low water temperature, improper hydrochemical regime, unsanitary condition of the aquarium, etc.), with inferior, uniform feeding. As a result of poor conditions of maintenance and nutrition, epithelial cells of the skin die and are the best substrate for life and reproduction of ciliates.

The causative agent of the disease is distributed with live food, water, soil and aquatic vegetation from reservoirs where wild fish live (especially in late winter and early spring), with acquired fish that have not been quarantined and not processed in therapeutic and preventive baths, with aquatic vegetation, soil and water taken from an aquarium unsuccessful for chylodonellosis, with common landings for all aquariums, landings, scrapers, feeders and other fish-breeding equipment.

Symptoms and pathogenesis. The parasite, moving along the surface of the skin, irritates the nerve endings, causing anxiety of the fish. At first, the fish makes oscillatory movements with the whole body, staying in one place or slowly moving forward. A careful examination of the surface of the skin, when the fish is located head to the observer, you can see a dull white shade that covers the body of the fish along the side line and above it.

With a more severe parasite attack, the fish rubs against plants and various objects located at the bottom of the aquarium (stones, shells, decorative roots, etc.). By this period, almost the entire body of the fish is covered with a bluish-gray coating, which is formed as a result of the protective reaction of the body and is due to intense mucus secretion. Due to abundant mucus secretion, skin respiration is disturbed, which in young fish plays a significant role in the general respiratory process. Fish behaves uneasily, often jumping out of the water. Some individuals who willingly took food before this period cease to eat.

The course of the disease is complicated by other ectoparasites (trichodins, gyrodactylus, etc.).

Often, an outbreak of chylodonellosis results in mass death of fish.

Diagnosis put on the basis of a microscopic examination of scrapings of mucus from the skin of the fish and the detection of the pathogen in them. According to the clinical signs and course, chylodonellosis is very similar to boneosis, trichodinosis and gyrodactyliosis.

Treatment. If the extent of invasion is quite large in the aquarium (almost all fish have a pronounced disease) and the death of the fish is observed, treatment in short-term baths is contraindicated, as the body of the fish is significantly weakened. In this case, the treatment takes into account the biological characteristics of the parasite. In the aquarium, the temperature of the water is raised to 30–32 ° C, while it is aerated. The set temperature regime is maintained until the fish begin to eat actively and get stronger. High temperature kills part of the parasites, but a certain amount of them is encysted. After lowering the temperature of the water to a normal cyst, it dissolves, and the parasite attacks the fish again. That is why treatment with an increase in water temperature does not completely release the population, soil and vegetation of the aquarium from the infectious beginning, but only temporarily relieve fish from parasites. Only after the fish are sufficiently strong (during this period they are intensively fed with live food), it is possible to start treatment in a separate vessel by treating the fish in short-term medicinal baths.

If chylodonellosis was diagnosed at the very beginning of the disease, and the fish are well-fed, treatment can be carried out in short-term baths without prior exposure to high temperature.

In the treatment of fish in a separate vessel, therapeutic solutions are used: potassium permanganate (KMnO4), the course of treatment lasts 7 days, copper sulfate (CuSO4• 5H2O), the treatment is carried out for four days, malachite green (strictly according to the method described in the book), the main purple K, bicillin-5.

With any of these methods of treating fish, fresh solutions of medications are prepared daily.

In the treatment of fish in a general aquarium, bicillin-5, methylene blue, malachite green with copper sulfate are used. The methods of using these drugs are described in the section “Treatment of fish in a general aquarium”.

Prevention is reduced to the creation of optimal conditions for keeping, proper feeding of fish and prevention of their dense plantings, especially in growing aquariums. Newly acquired fish should be quarantined and passed through antiparasitic baths.

The pathogen should not be allowed to enter from water bodies where wild fish live, as well as from aquariums that are unsuccessful for this invasion.

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