Oodiniasis, Velvet disease, Gold spot disease, Coral fish disease.
Contagious disease. One of the most common parasitic diseases of aquarium fish. The causative agents are three independent flagellates, two of which (Oodinium pillularis and Oodinium limneticum) parasitize freshwater aquarium fish, and the third (Oodinium ocellatum, synonym Branchiophilus maris) parasitizes marine aquarium fish. Oodiniasis in free-living fish in natural water bodies has not been registered in our country. Therefore, the main sources of the disease pathogens are exotic fish, aquatic vegetation, mollusks, substrate, and water from tanks affected by oodiniasis.
Oodiniasis is one of the most common parasitic diseases of freshwater aquarium fish of all species and age groups. Fish from the genera Tanichthys, Nothobranchius, Hyphessobrycon, Nannostomus, Puntius, Brachydanio, and Danio, as well as from the order Cyprinodontiformes and the family Labyrinthici (Anabantidae/Osphronemidae — dwarf gouramis, Siamese fighting fish, and paradise fish) are most susceptible. Fish of the family Cichlidae are the least susceptible, although all of them can be carriers of Oodinium.
Oodinium pillularia (Piscinoodinium pillulare) — The parasite actively swims in the water and, having found a fish, attaches to its surface with its pointed end, after which it penetrates under the epithelium of the skin, fins, gill apparatus, and oral mucosa. Here the parasite, actively feeding on the tissues of the victim, grows and after some time, which directly depends on water temperature, enters the external environment. At a temperature of 25°C, the feeding stage is completed in four days, at 20°C — in five days, at 30°C — in two days.
Having left the fish, the parasite becomes spherical, covers itself with a dense protective shell (cyst), settles to the bottom or plants, and begins to divide repeatedly in two, resulting in the formation of 32 to 64 young individuals. Having ruptured the cyst, they enter the water and for some time lead a non-parasitic lifestyle similar to algae, carrying out photosynthesis, which is why during this period they need bright, especially sunlight. However, Oodinium cannot live for a long time without a host and swim precisely in search of a fish; having found one, they immediately penetrate under the epithelium of the external tissues, and their development cycle repeats.
Oodinium limneticum (Piscinoodinium limneticum). Attacking a fish, this parasite does not penetrate under the epithelium, but remains on it, attaching with pseudopodia, growing and increasing in size. In approximately the same timeframes as O. pillularia, it covers itself with a cyst without leaving the fish. In the reproduction stage through multiple transverse division under a dense shell, about 200 daughter organisms are formed. Ripping the cyst, some of them settle on the previous victim, and some set off to look for a new one, actively swimming in the water for three days. If the parasite does not find a fish during this time, it dies.
Oodiniasis is an insidious disease. It can linger in an aquarium setup for years, and the owner may not even suspect it. Adult fish very rarely die from oodiniasis. If the maintenance conditions are good, the fish only act as carriers of the infection. They do not even get sick in an overt form. Sometimes, for no apparent reason, they scratch against stones and plants, and also suddenly turn pale and twitch sharply.
Sometimes, especially in good conditions, the disease in adult specimens proceeds sluggishly, with weakly expressed signs of illness, and only an experienced and very attentive aquarist can recognize the disease in time and make a preliminary diagnosis. Fry and immature fish are more susceptible to the disease than adult exotic fish. The infestation develops slowly, with insignificant mortality among sick fish. Oodinium enter the aquarium along with fish, plants, water, and equipment from an infected aquarium.
Parasites, destroying the epithelial layer of the skin and fins of fish, cause intensive mucus secretion, which leads to impaired cutaneous gas exchange. The impairment of the latter is especially dangerous for fish fry, whose gill apparatus is still poorly developed, and blood oxygenation occurs mainly through the skin covering the entire body surface. Without experience, advanced oodiniasis can be confused with the tropical form of ichthyophthiriasis. In practice, it is important to be able to distinguish oodiniasis from ichthyophthiriasis, since the treatment methods for these diseases are different. But there are also significant differences: in ichthyophthiriasis, the coating on the body of the fish is white, the grains are larger and more reminiscent of semolina, fish lose their appetite, and signs of suffocation are more pronounced.
Symptoms: •— In some cases, fish behave restlessly, often scratching against the substrate and plant leaves; in others, on the contrary, they are depressed and sluggish. In the initial stage of the disease, the fish stays in the corners of the aquarium, swimming in jerks. Appetite is maintained in fish until death. However, visible manifestations of the disease become noticeable only at the stage of severe infection. •— Oodinium infection usually starts from the fins and then spreads all over the body. The dorsal and caudal fins appear glued together, and the inter-ray tissue is destroyed. Only broken rays remain without inter-ray tissue. In long-finned high-finned fish, the fins stick together and hang limply, and later split between the rays.
•— Sick fish develop a very characteristic sign: tiny nodules on the surface of the body and fins, perceived by the naked eye as golden or silvery flour dust. In the next stage of the disease, the fish looks as if it has been sprinkled with flour; a velvety coating appears on the skin, which is why this disease is also called “velvet disease”. This coating is especially noticeable when looking at the fish along its body. Tiny yellow-green spots completely cover the entire body. Individual areas of skin and fins acquire a grayish-brown tint as the number of parasites increases. •— Over time, mucus is secreted abundantly, the outer integuments peel off in flakes, and the skin in places sloughs off the fish in shreds. With the development of the disease, the destruction of the skin epithelium increases, leading to its flaky peeling. •— Irritating the skin integuments and gill apparatus, parasites cause intensive mucus secretion, which extremely complicates gill and cutaneous respiration, especially in fry.
Treatment: Sick fish are treated both in a separate vessel and in the general aquarium. It is believed that only free-living stages of these protozoa are susceptible to medications. Elevated temperature accelerates the life cycle of these parasites, so they emerge from the encysted stage earlier and become vulnerable to treatment. Due to this, the required treatment period is shortened.
However, in case of severe fish infestation, this method should be avoided due to the danger of exacerbating existing respiratory problems. The rapid reproduction of parasites can be reduced by keeping the aquarium in the dark, thereby preventing photosynthesis in parasites at the free-living stage. This method is useful for reducing the further reproduction of protozoa in cases where fish have already received a heavy load of these parasites. However, it should only be used in combination with medications.
Having diagnosed the disease, treatment must be started immediately, even if the parasite infestation seems insignificant. To do this, all fish from the infected aquarium must be transplanted into a separate vessel with water at a temperature of 25-27°C and treated on the first day with a trypaflavine solution (0.2 g per 10 L of water) for 20 minutes or a malachite green solution (0.006 g per 10 L of water) for 5 hours, after which they should be moved to another aquarium with clean water and fed with live tubifex or bloodworms 6-7 hours later. On the second day, add a solution of Basic Violet K (Gentian Violet) (0.002 g per 10 L of water) to the aquarium and, providing sufficient aeration and live food, keep the fish for four days, after which transfer them to an aquarium with clean water. On the sixth and seventh days, fish must be briefly treated with copper sulfate for 20 minutes, after which they can be returned to the general aquarium. The water temperature in the general aquarium, from which all fish have been removed, is raised to 29-30°C and maintained at this level until the fish treatment is completed. Fish farming equipment must be disinfected.
If fish treatment is carried out in a separate vessel, the water, substrate, and vegetation are left in the fishless aquarium for 7-8 days. At the same time, the water temperature is constantly maintained at 29-30°C, and the aquarium is brightly lit. During this time, parasites without fish die. All fish are transplanted into a separate vessel for 14 days and kept at a temperature of 25-27°C with bright lighting, and treatment is carried out. Then the fish that have undergone the course of treatment in baths are returned to the aquarium, and the equipment is disinfected. After the disease is suppressed, the fish remain with severely damaged skin integuments. Characteristic bald patches formed at the site of mass accumulations of parasites. Measures must be taken to prevent secondary infections on the affected skin.
Medications: Aquarium Pharmaceuticals Exodin; Aquarium Pharmaceuticals General Cure; Aquarium Pharmaceuticals Triple Sulfa; Aqua Medic exodin; Aqua Medic pointex; Sera omnisan; Sera oodinopur; Tetra Contra Ick plus; Acrimet; Antipar; Biomycin; Ichthyophor; Malachite green with copper sulfate; Basic Violet K; Rivanol; Table salt, sea salt; Copper sulfate; Trypaflavine; Metronidazole (Trichopol); Formalin; Formamed; Quinine;
Prevention: To prevent the spread of the disease pathogen, we recommend keeping newly acquired fish for a month in a separate container, prophylactically treating them three times with one of the approved medications for treatment. Do not forget about disinfecting acquired aquatic vegetation and assigning dedicated fish-keeping equipment to each aquarium.
