Causes: Crab ciliary disease is a parasitic disease that often occurs in autumn river crabs. The pathogen is caused by ciliates parasitic on the body surface, appendages, gills and other parts of crabs. Common in fish and crab mixed culture water surface, both young and adult crabs can be infected. The causes of this disease are: the water level of Chihu Lake is reduced, the water resources are negatively growing, and the stocking density of fish and crabs is too high, too much feeding and fertilization in summer, long-term accumulation of excreta, and no disinfection and sterilization when seedlings are cast. Main symptoms and harmfulness: There are many yellow-green or brown villi on the body surface of the sick crab, and the body surface and appendages have a greasy feeling. Once a crab is infected with ciliary disease, its appetite will decrease, and its body will be emaciated and its shape will be slow, which will seriously affect its shelling and growth. At the initial stage of the disease, there were no obvious symptoms on the body surface of shrimps and crabs, but they were slow to move and react to external stimuli. The water flowing out through gills was slow, and the mucus on the body surface felt greasy. Microscopic examination of gill filaments and appendages of diseased shrimps and crabs showed a small number of ciliated protozoa and filamentous algae, such as bell worms, cladoptera and oblique worms. When the disease develops to the middle stage, the naked eye can already tell that the diseased shrimp and crab have a small amount of yellow-green or brown fluff on their bodies. When three to five worms are found in one field of vision through microscopic examination, it can be considered that the disease has developed to the middle stage. Microscopic examination shows that there are more than five worms in one field of vision, with thick attachments on the whole body, sludge hanging on the gills and increased mucus, which can be judged as serious infection. Anatomical observation shows that the jejunum, the liver is light yellow or dark brown or patterned, the muscles are inelastic, and the gills are black. At this time, bacterial diseases are often secondary. It is more difficult to get treatment at this level.