Costiosis, Costiaisis, Ichthyobodosis.
A contagious disease caused by the flagellate protozoan Ichthyobodo necatrix (formerly known as Costia necatrix), belonging to the family Bodonidae, order Protomonadina. Its body is oval or teardrop-shaped, 8-12 µm long, with two flagella used by ichthyobodo to swim and attach to the skin and gills of fish. Costia destroy fish skin tissue and cause very heavy mucus secretion. Protozoan parasites causing this disease are often present in small numbers on fish that appear completely healthy. However, when fish experience weakened immunity due to adverse environmental conditions, including stress, these parasites can multiply to dangerous numbers.
They enter the aquarium along with food, plants, and substrate from water bodies where fish live, as well as with fish, plants, water, and equipment from an infected aquarium. Outbreaks are promoted by high water temperatures, acidic pH 6.0, and unchanged water. Disease outbreaks can be observed year-round, but most frequently in the early summer months when the parasite is widespread in nature and introduced with live food. Poorly treated bloodworms and tubifex can introduce resting-stage Costia necatrix into the aquarium.
If the parasite does not find a host within a few hours, it dies. This should be taken into account when fighting the disease: it is enough to catch all the fish from the infected aquarium, raise the temperature to an optimal 25-27°C, and these pathogenic protozoa will be eliminated within a few hours. A temperature of 30-32°C is fatal to the parasite, therefore, it is advisable to give therapeutic baths to fish in warm water. The question may arise: why create favorable conditions for them when combating the causative agent of costiosis in the aquarium?
The fact is that otherwise, the parasite’s body rounds off, partially loses mobility, and in this state can remain viable for a long time. In favorable conditions, however, ichthyobodo becomes active in search of a host, quickly depletes its energy reserves, and dies. If the parasite manages to find a host—which can be an aquarium fish of any species and age, especially young ones—it attaches to the body surface or gill apparatus using a specially adapted finger-like outgrowth, and then, feeding on surrounding epithelial cells, rapidly multiplies by longitudinal binary fission.
Under favorable conditions, the entire body surface and gill apparatus of the affected fish soon become literally dotted with tiny organisms. Feeding on epithelial cells, ichthyobodo causes irritation of the skin and gill lamellae tissues, destruction of surface cells, and excessive mucus secretion, leading to the fish’s death from suffocation. The invasion of the parasite causes severe skin irritation and excessive mucus production, which the parasites feed on. The disease is most dangerous for fry. Underconditioned fish tolerate the disease poorly, especially in acidic, poorly aerated, and unchanged water. Adult fish rarely die from costiosis, but they become carriers of the pathogen. If left untreated, the fish dies.
Clinical signs of chilodonellosis, apiosomiasis, trichodiniasis, and gyrodactylosis often overlap with symptoms of costiosis. They can sometimes be differentiated only by examining a skin scraping and gill smear of the sick fish under a microscope. Therefore, hobbyists usually treat the disease taking into account the features of all these conditions. Fortunately, in practical terms, this is not critically important since, except in advanced cases, the treatment for these diseases can be identical. Cysts formed by Costia are very resistant to external influences and do not die during treatment, so the disease may flare up again after some time. This usually happens with very high stocking densities, insufficient or poor nutrition, and keeping fish in acidic water (pH 5.5 and lower).
Symptoms: •— In the early stage of the disease, skin irritation bothers the fish, and they constantly rub against substrate and plants. •— The fish stops feeding. Does not react to stimuli. •— Labored breathing; they begin to gulp air even when oxygen levels in the aquarium are adequate. •— The fish makes rocking movements with clamped fins. •— Fins are clamped. Sometimes fin degradation is observed, characterized by necrosis of the inter-ray tissue. Fin rays become exposed. •— Around the eyes, on the upper back, and at the base of the tail, a bluish coating can be seen upon close inspection. When viewed from above, this coating is clearly visible.
•— Excessive mucus production makes the skin look dull. Most often, such changes are observed between the head and dorsal fin, but can cover most of the head and body. The skin appears rough, and in severe cases, scales and skin may peel off in strips. •— A little later, blue-gray patches appear on the body of sick fish, turning into a grayish or milky veil (solid gray coating) due to abundant mucus secretion, sometimes with delicate pinkish-red spots. Isolated slightly reddened areas. Due to increased mucus production, the sides of the sick fish’s body become covered with a turbid bluish-gray coating. This coating may have a bluish tint, caused by intensive mucus production. The most affected areas undergo decomposition.
•— In addition, flared gill covers of the fish are clearly visible from above. A thick layer of gelatinous mass tightly closes the respiratory folds. A grayish-white mucous coating extends from the gill slit. The affected gills become pale, anemic, and covered with mucus that hinders the assimilation of dissolved oxygen from the water. Alternation of bright red and white areas on the gills, various deposits, hemorrhages, adhesion, and necrosis of gill lamellae. Breathing with such gills is impossible. •— Secondary bacterial or fungal infections may develop in areas with severe skin damage.
Treatment: Treat the entire aquarium along with its inhabitants, because it is logical to assume that all fish in the infected aquarium are also infected to some degree. The following treatment regimen is most effective in this case. During the first two days, raise the temperature in the infected aquarium to 32-33°C with mandatory artificial aeration and feeding the fish live bloodworms or tubifex twice a day. Costiosis pathogens tolerate “heat” poorly, and some of them die already at this stage of treatment.
On the third day, all fish must be caught from the general aquarium and placed in a separate vessel with a solution of common salt (100 g per 10 L of water) for 30 minutes, after which the animals are transferred to another container with clean water and fed live bloodworms after 3-4 hours. On the fourth day, the fish are treated with a copper sulfate solution (1 g per 10 L of water) for 20 minutes, then transferred to a container with clean water, and fed bloodworms after 6-7 hours. On the fifth day, a solution of Basic Violet K (0.002 g per 10 L of water) is added to the container, and the sick fish are kept in it for five days, providing sufficient aeration and live food.
After that, the fish are returned to their “home” aquarium, raising the temperature in it to 32°C for two days, and then lowering it to optimal levels. Special attention should be paid to the temperature regime in the “sick” aquarium. For all ten days while there are no fish in it, the water temperature optimal for most parasitic disease pathogens (24-27°C) must be maintained. During this time, the parasites manage to activate and, failing to find hosts, perish.
In cases of mass severe costiosis, treating fish directly in the main aquarium usually yields no results. In this case, treatment should be carried out using short baths with antiparasitic solutions. For this purpose, the following short baths are used: potassium permanganate solution – treatment course 5 days; common salt solution – treatment course 7 days; chemically pure copper sulfate solution – repeated daily for four days; malachite green solution; Basic Violet K solution; formalin solution.
If it is impossible to treat fish in a separate vessel, medicinal preparations are applied by adding them to the general aquarium. The water, substrate, and plants in the aquarium from which sick fish were removed for treatment are not changed. The fish are removed, and raising the water temperature for 10-12 hours a day to 30°C with simultaneous aeration for 5-8 days leads to the destruction of the parasites. In the absence of fish, the pathogens die in less than a day. For prophylactic purposes, the water temperature in the aquarium can be raised to 32-34°C for two days. After the treatment is completed, the fish are returned to the aquarium and intensively fed fresh food.
Medicines: Aquarium Pharmaceuticals Triple Sulfa; Sera costamed; Sera costapur; SERA med Professional Protazol; Sera Omnipur; Tetra Contra Ick plus; Tetra Fungi Stop; Tetra General Tonic; Tetra Gold Oomed; Tropical Ichtiosan Pond; Antipor; Biomycin; Malachite green; Methylene blue; Metrifonate; Basic Violet K; Rivanol; Common salt, sea salt; Copper sulfate; Trypaflavin; Formalin; Formamed; Furacilin.
Prevention: Newly acquired fish are kept in quarantine for 30 days. Then they are passed through one of the therapeutic and prophylactic short baths three times and only after that transferred to the general aquarium. Water used for storing live food must not enter the aquarium, nor should plants, substrate, and water from a natural water body, infected or unknown aquarium be introduced without necessary treatment, and the same equipment should not be used in healthy and infected aquariums. In addition, ichthyobodo multiply most intensively in an acidic environment (pH 4.5-5.5), so maintaining a pH of 7-7.5 in the aquarium can be considered an additional preventive measure against costiosis.
