Rotifers are a genus of protozoan phylum cilia, a species of ciliate. There are more than 70 species in both light and seawater, with a size of 40 to 100 μm, and the body is disc-shaped or bell-shaped. The dorsal surface is protruding, with an opening in the middle to form a cellopharynx, with two rows of parallel spiral-shaped long cilia, and the ventral concave surface forms an adhesion, consisting of 3 layers of concentric circles arranged in rings. The inner ring is toothed, called a toothed ring or a crown ring, the number, size and shape of the toothed ring vary according to the type of wheel worm, which can be used as the basis for classification; the second layer is a band ring, which overlaps with the toothed ring and is arranged in radial lines outward; the edge of the outer ring is composed of a soft film, there are many cilia on it, which can swing and move, and the ring rotates like a wheel when moving, so it is called a wheel worm.
Wheelworms reproduce mainly by dichotomy and also undergo joint reproduction. It feeds on plankton in the water and epithelial cells shed by the fish body, which is only a place for its epiphytes. As the wheelworm crawls and moves on the fish body, its attachments, such as toothed rings or cilia, irritate the epithelial tissue of the fish body. In ponds with poor water quality or too much organic matter, carous worms multiply in large numbers, epiphytic wheelworms cause necrosis and peel off the epithelial cells of the fish, causing wounds and causing bacterial infections, and pond fish die from rotten gills or rotten fins. In addition to parasitizing tissues such as gills and body surfaces, rotifers can also parasitize in the intestine, reproductive tract or urinary tract, but do not cause special lesions.
Symptoms: parasitizing on the surface and gills, fry may have "white heads and white mouths" or "running horses" (circumnavigating) symptoms. Sick fish appear as black bodies and swimming alone. Some swim wildly around the pond in groups, often causing a large number of deaths of fry and fingerlings. The chakra parasitic on the surface of the fish slides back and forth on the surface of the fish body, stripping the host's skin tissue cells and gill tissue for nutrition, destroying the skin and gill tissue, affecting the fish's breathing and normal activities. It should be noted that silver carp have similar symptoms of wheelworm disease and bleeding disease. Due to the parasitism of wheelworms. When silver carp gills are parasitic with wheelworms, the gill surface will continue to secrete mucus, and a large amount of mucus will cause the silver carp to reduce its ability to absorb oxygen. Silver carp swim on the surface of the water for a long time in order to obtain the oxygen they need, causing the fins to be congested. At the same time, a large amount of swallowed air enters the intestine, and the dissection finds that these large amounts of swallowed air cause the intestinal wall to be congested and inflamed, and some fish maw walls also show a bloody state.
Diagnostic methods can be definitively diagnosed by microscopic examination of the gills and mucus on the surface of the body for the presence of wheelworms. The diseased fish is stimulated by the parasite of the insect body, causing the tissue to become inflamed, secreting a large amount of mucus, and forming a layer of mucus in the body and gills. The sick fish are emaciated and blackened, swimming slowly, and sometimes the sick fish do intermittent concentric circles on the surface of the water and jump.