Cryptobiosis.
An infectious disease. Cryptobiosis is a parasitic fish disease caused by flagellates — single-celled parasites belonging to the order Bodonidea, family Bodonidae, and genus Cryptobia. Two species affect fish: Cryptobia cyprini and C. branchialis. These flagellates parasitize the blood and gill apparatus of fish. Fish of the genus Carassius (goldfish) are most susceptible to cryptobiosis. Adult fish fall ill less frequently, acting as carriers of cryptobia, whereas in juveniles the disease often takes an acute form, causing mass mortality. In water, the parasite actively swims and, in the absence of fish, dies within 1-2 days. Externally, these parasites are similar to each other, but their life cycle and the symptomatology of the diseases they cause are so different that they must be considered separately.
Branchiopathic cryptobiosis is caused by the single-celled parasite Cryptobia branchialis. Among aquarium fish, varieties of the goldfish are most susceptible to cryptobiosis, but many other fish species can also serve as parasite carriers and fall ill under adverse conditions. Settling on the gills, the parasite begins to reproduce intensively by longitudinal fission. Some of the daughter cells leave the host in search of a new victim and can swim freely in the water for up to two days, after which the cryptobia die.
Having found a fish, the young parasite attaches itself to the epithelium of the gill lamellae using its posterior flagellum, tears it, thereby disrupting the respiratory function of the gills and providing itself with nourishment, after which it continues to reproduce. In severe cases, all fish in the aquarium can die in just a few days. Affected gills acquire an unusual bright red color. At the beginning of the disease, a lot of mucus appears on the body of the fish, making them paler than usual. However, shortly before death, the body of the sick fish darkens significantly. From the very beginning of the disease, the fish become sluggish, refuse food, and show signs of suffocation. The disease can be complicated by branchiomycosis.
To combat the disease, all fish are placed in a separate vessel and treated for short periods with preparations: on the first day — with copper sulfate (1 g per 10 L of water, exposure for 20 min); on the second — with formalin (2.5 ml per 10 L of water, exposure for 30 min); on the third — with malachite green (0.006 g per 10 L of water, exposure for 5 hours); on the fourth day, the fish are returned to the general aquarium, where the parasites have died from exhaustion during the treatment period without finding a host. Prevention of branchiopathic cryptobiosis consists in preventing the parasite from entering a healthy aquarium, either from an infected aquarium or from a natural body of water. Acquired fish must be placed in a 30-day quarantine with three preventive treatments using copper sulfate at a therapeutic dosage with an interval of 15 days between treatments.
Hemopathic cryptobiosis is caused by the single-celled parasite Cryptobia cyprini. In the aquarium, it is found in many fish, but is especially dangerous for goldfish. In natural and aquarium conditions, it can reproduce only with a change of hosts. The primary hosts are fish, and the intermediate hosts are blood-sucking leeches, in the intestines of which the flagellates multiply and, when a leech attacks a fish, pass into the latter’s circulatory system. Unlike C. 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, which served as its intermediate host.
If a leech attacks a fish sick with cryptobiosis, the causative agent enters the leech’s intestine with the blood and begins to multiply intensively asexually. From the intestine, the parasites penetrate into the cavity of the leech’s proboscis, and from there through a wound into the bloodstream of another fish. In sick fish, the gills are pale, and blisters filled with clear pinkish fluid often form on the body. Internal organs and tissues are pale and flabby, the gallbladder is overflowing with bloody fluid, and the blood clots poorly.
Methods for treating cryptobiosis caused by C. cyprini have not been developed. Treatment can be effective only in the early stages of the disease: methylene blue is added to the food (bread crumb is convenient for this) at the rate of 0.1 g of the preparation per 100 g of food. Preventive measures are simple. It is sufficient to prevent blood-sucking leeches from entering the aquarium, which sometimes get in with live foods or plants from a natural body of water.
