How to identify and prevent common diseases of Chinese mitten crab?
The Chinese mitten crab is an economically important crab species, also known as river crab, hairy crab, and clear-water crab, and is a long-renowned delicacy in China.In recent years, high-density, high-input, high-output farming models have greatly boosted the enthusiasm of Chinese mitten crab farmers and improved economic returns. Disease in Chinese mitten crabs is one of the key factors affecting high yields. In actual farming practice, what are the common diseases of Chinese mitten crab and how are they prevented and treated?
I. Types and symptoms of common diseases of Chinese mitten crab
1. Saprolegniasis
Main symptoms: Grayish-white cotton-like mycelia 2cm~3cm long appear on the body surface, appendages, or wounds of diseased crabs and multiply extensively, penetrating deep into the muscles and spreading into the spaces between tissues. After the body surface is irritated, the Chinese mitten crab secretes large amounts of mucus, moves slowly, loses appetite, and becomes thin and weak. Tissue at the wound site ulcerates and spreads, and the crab finally dies because it cannot molt.
2. Edema disease
Main symptoms: The abdomen, abdominal muscles, and area below the carapace of diseased crabs become swollen and transparent. They move slowly, linger on the shore, do not enter the water, do not feed, and finally die of exhaustion. This disease is caused by bacterial infection after injury to the abdomen of the Chinese mitten crab.
3. Enteritis disease
Main symptoms: Diseased crabs lose appetite, move slowly, and their body color turns pale. After dissection, the intestine is found to be red with no food and no feces. Sometimes the liver, kidneys, and gills also develop lesions, and sometimes gastric ulcers occur with yellow fluid being vomited from the mouth. Sometimes the liver, kidneys, and gills also develop lesions, and sometimes gastric ulcers occur with yellow fluid being vomited from the mouth.
4. Black gill disease
Main symptoms: In the early stage of the disease, some gill filaments appear dark gray or black. As the disease progresses, all gill filaments turn black, the gill filaments become incomplete, and the tips and respiratory organs necrose. Breathing becomes difficult and movement slows. Crabs often stay on the shore or attach to aquatic plants, and in severe cases die within a few days.
II. Treatment methods for common diseases of Chinese mitten crab
1. Treatment methods for saprolegniasis
Soak diseased crabs in a 3%~4% saltwater solution for 3min~5min, or soak them in a 3g/m3~5g/m3 solution of Saprolegnia cure (main ingredient: Chinese gall) for 25min~30min.
Splash dibromohydantoin (main ingredient: dibromohydantoin, specification 10%) over the whole lake, with a dosage of 150g/acre/m~200g/acre/m at depth.
Splash Saprolegnia purifier (main ingredients: Chinese gall, Forsythia suspensa, sulfadimidine, synergist) over the whole lake at a dosage of 50g/acre/m, which may be increased to 50g/acre/m~80g/acre/m when there is a lot of Saprolegnia.
2. Treatment methods for edema disease
Splash calcium oxide (quicklime) over the whole lake at a dosage of about 15kg/acre/m, adjusting the pH value to between 7.5 and 8.5.
Broadcast quick-acting bottom stabilizer (main ingredients: tetrakis(hydroxymethyl)phosphonium sulfate, high-osmosis bactericide, adsorbent, decomposer, chelating agent, etc.) over the whole lake at a dosage of 150g/acre/m~200g/acre/m, once daily for 2 consecutive times.
Broadcast granular bacterial purifier (main ingredients: bromochlorohydantoin, calcium peroxide, oxidant, etc.; content specification: 100g:24g) over the whole lake at a dosage of 150g/acre/m~200g/acre/m, once every other day for 2 consecutive times.
3. Treatment methods for enteritis disease
Mix bacterial and viral killer (main ingredients: Coptis chinensis, Scutellaria baicalensis, Phellodendron amurense, Rheum officinale, Gardenia jasminoides, Euphorbia humifusa, Isatis indigotica, Lonicera japonica, Houttuynia cordata, immunoenhancer) into feed and feed it, with a dosage of 40g~50g per 10 kg of feed for 3d~4d consecutively.
Splash povidone-iodine solution (main ingredient: povidone-iodine, a complex of 1-vinyl-2-pyrrolidone homopolymer and iodine; specification: 10%) over the whole lake at a dosage of 300ml/acre/m~500ml/acre/m, once every other day for 2~3 consecutive times.
Splash bis-quaternary ammonium salt complexed iodine (main ingredients: di-octyl/decyl dimethyl complexed iodine, stabilizer, complexing agent, etc.; raw material specification: quaternary 40% iodine 4%) over the whole lake at a dosage of 100g/acre/m~150g/acre/m, once every 2d~3d for 2~3 consecutive times.
4. Treatment methods for black gill disease
Splash calcium oxide (quicklime) over the whole lake at a dosage of 10kg/acre/m~15kg/acre/m to keep the aquaculture water weakly alkaline.
Splash strong disinfectant (main ingredient: sodium dichloroisocyanurate; specification: 20%) over the whole lake at a dosage of 180g/acre/m~200g/acre/m, once daily for 3 consecutive times.
Splash bromochlorohydantoin powder (main ingredient: bromochlorohydantoin; specification: 24%) over the whole lake at a dosage of 80g/acre/m~110g/acre/m. Once daily for 2 consecutive times.