Diseases Caused by Flagellates.
Protozoan diseases are caused by protozoan parasites. Protozoa belong to three classes: Mastigophora, Sporozoa, and Ciliata. Protozoa are single-celled organisms. They can be found under a microscope, although some are visible to the naked eye. Some of them are classified according to their mode of locomotion. For example, ciliated protozoa are bordered by hair-like structures (cilia) that move and propel the animal forward. At the same time, flagellated protozoa use flagella for the same purpose. Among ciliated protozoa, there are both free-living and parasitic species, including a number of fish parasites. Some of the most common diseases of aquarium fish are caused by protozoan parasites.
Ichthyobodo. These are flagellated protozoan ectoparasites that affect fish (synonym Costia), belonging to the family Bodonidae, order Protomonadina. Its body is oval or teardrop-shaped, 10-12 µm long, with two flagella used by Ichthyobodo to swim and attach to the fish’s skin and gills. These parasites are one of the possible types of pathogens causing a disease manifested by excessive skin mucus production. In addition to the parasitic stage, these protozoa have a free-living stage in water and are present in small numbers in the aquarium. Apparently, they begin to multiply rapidly only when the fish’s immunity is suppressed due to unfavorable environmental conditions or other diseases.
They can infect many species of fish and feed on their host’s skin. Young fish are especially susceptible to infection – even under favorable environmental conditions. These parasites prefer temperatures below 25°C and die at 30°C. There are reports of a resistant cyst stage, which can be a potential source of reinfection. They enter the aquarium with food, plants, and substrate from a body of water where fish live, as well as with fish, plants, water, and equipment from an infected aquarium.
Ichthyobodo necatrix (formerly called Costia necatrix). A flagellate that causes the parasitic disease Ichthyobodiasis, or Costiosis. A dangerous parasite parasitizing the skin and gills. If the parasite does not find a host within a few hours, especially at a temperature of 29-32°C, the ectoparasite dies within a day. If the parasite manages to find its victim, which can be an aquarium fish of any species and age, especially a young one, it attaches to the surface of its body or gill apparatus with a specially adapted finger-like outgrowth, then, feeding on the surrounding epithelial cells, it rapidly multiplies by longitudinal binary fission.
Under favorable conditions, the entire surface of the body and gill apparatus of the affected fish soon becomes literally dotted with tiny animals. Adult fish get sick very rarely, but can be carriers of the parasite. Outbreaks of the disease can be observed all year round, but most often in the early summer months when it is widespread in nature and introduced with live food.
Piscinoodinium. A synonym for this name is Oodinium. Oodiniums belong to the class Phytomastigophorea, order Dinoflagellida. The pathogens 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. This parasite infects many species of fish, but is most often observed in barbs and other cyprinids, as well as gouramis and killifish. The life cycle of this parasite includes both a parasitic stage and a free-swimming stage. The duration of the life cycle depends on temperature, and the higher the temperature, the faster this cycle accelerates. Piscinoodinium is capable of photosynthesis, and light plays an important role in its development.
In a tropical aquarium, these parasites can multiply astonishingly quickly, so that the fish living in the aquarium will be constantly attacked by new hordes of infectious dinospores. In our country, Oodinosis in free-living fish in natural water bodies has not been registered. Therefore, the main sources of disease pathogens are exotic fish, aquatic vegetation, mollusks, substrate, and water from aquariums affected by Oodinosis.
Oodinium (Piscinoodinium) pillularia – It is covered with cilia and equipped with two flagella. The parasite actively swims in the water and, having found a fish, attaches to its surface with a 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 host’s tissues, grows and after some time, which directly depends on the water temperature, leaves the fish, drops to the bottom or plants, where it multiplies. At 25°C, the feeding stage is completed in four days, at 20°C in five days, and 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 lead a non-parasitic lifestyle similar to algae for some time, performing photosynthesis; therefore, during this period they need bright, especially sunlight. However, oodiniums cannot live for a long time without a host and swim precisely in search of fish, having found which, they immediately penetrate under the epithelium of the outer tissues, and their development cycle repeats.
Oodinium (Piscinoodinium) limneticum. Parasitizes the skin and fins, where it multiplies. When attacking a fish, this parasite does not penetrate under the epithelium, but remains on it, attaching with pseudopodia, grows, and increases in size. In approximately the same timeframes as O. pillularia, it becomes covered with a cyst without leaving the fish. In the reproduction stage by multiple transverse division under a dense shell, about 200 daughter organisms are formed. By rupturing the cyst, some of them settle on the previous victim, and some go in search of a new one, actively swimming in the water for three days. If the parasite does not find a fish during this time, it dies.
Cryptobia. Flagellates belonging to the order Bodonidea, family Bodonidae. The genus Cryptobia includes two species – Cryptobia cyprini and Cryptobia branchialis. Outwardly, these parasites are similar, but their lifestyle and the symptomatology of the diseases they cause are very different. Protozoan disease caused by flagellates parasitizing the blood and gill apparatus of fish. Branchial cryptobiosis is caused by the unicellular parasite Cryptobia branchialis, which has a somewhat elongated body and one flagellum at each of the rounded anterior and pointed posterior ends of the body. Hemopathic cryptobiosis is caused by the unicellular parasite Cryptobia cyprini. In natural and aquarium conditions, it can only reproduce with a change of hosts.
The primary host is fish, and the intermediate host is blood-sucking leeches, in the intestines of which the flagellates multiply and, when the leech attacks a fish, pass into the circulatory system of the latter. Unlike Cryptobia branchialis, the causative agent of hemopathic cryptobiosis settles not on the gill apparatus, but in the bloodstream of fish and is spread by blood-sucking leeches that served as its intermediate host. If a leech attacks a fish sick with cryptobiosis, the pathogen enters the leech’s intestine with blood and begins to multiply intensively asexually there. From the intestine, the parasites penetrate into the proboscis cavity of the leech, and from there through a wound into the bloodstream of another fish. Infection occurs through a sick fish. Goldfish are most susceptible. In the absence of fish, the parasite dies within 1-2 days.
Trypanosoma. This is a group of protozoan flagellates. They are found in wild specimens. They affect the blood. Transmission occurs through leeches; in their absence, infection stops. In the early stages, it is quite difficult to distinguish this disease from costiosis and trichodiniosis without a microscope. Fortunately, in practical terms, this is not so important, because, except for advanced cases, the treatment of these diseases can be the same.
Hexamita truttae. Synonym Octomitus truttae. Intestinal parasites. Affects the gallbladder and intestines of fish. In the host’s intestine, the parasite emerges from the cyst and subsequently localizes mostly in the anterior intestine and gallbladder, causing first irritation and then inflammation of the mucous membrane of these organs. In the intestinal cavity and gallbladder, hexamitas multiply by direct binary fission. Then some of them become encysted and excreted with feces into the water, creating a potential danger of infecting other fish. These protozoa live in small numbers in the intestines of cichlids and are sometimes found in fish of other families.
It is believed that they are the cause of hole-in-the-head disease. This disease is also known as head and lateral line erosion. In discus, as some researchers believe, Hexamitiasis is caused by its own parasite Hexamita symphysodonis. It enters the aquarium from water bodies along with food, plants, and substrate if they were not boiled or calcined, as well as with fish, plants, water, and equipment from an infected aquarium. It cannot withstand a temperature of 35°C. Young fish get sick more often than adults.
Protopalina symphysodonis. Intestinal parasites. Disease Protopalinosis. Infection of internal organs, especially the stomach. Dark coloration with mucous spots, clamped fins. More common in discus and kissing gouramis. The color changes to dark brown, and bellies swell. The disease leads to the death of the fish. Trichopolum is used in food or water. Sodium sulfacyl, Etazole, Furagin, Streptocid.
Spironucleus. A diplomonad flagellate. Disease Spironucleosis. Gill degeneration, bloated belly, whitish excrement, parasite of internal organs (mainly intestines). Not dangerous in nature, but extremely aggressive during mass reproduction in a limited volume. Trypaflavin, Tinidazole in food, Dimetridazole, Trichopolum are used.
