Common Diseases in Crayfish Farming and Their Prevention and Treatment Methods
Crayfish, also known as red swamp crayfish, red claw crayfish and freshwater crayfish, is a freshwater economic shrimp species that is widely popular for its delicious meat. Because of its omnivorous diet, fast growth rate and strong adaptability, it has formed an absolute competitive advantage in local ecological environments. Its feeding range includes aquatic plants, algae, aquatic insects, animal carcasses and so on, and when food is scarce it will even cannibalize its own kind. In recent years, crayfish has become an important economic aquaculture species in China.What are the common diseases in crayfish farming? How are they prevented and treated?
I. Common Diseases in Crayfish Farming
1. Soft shell disease
Causes: Insufficient calcium intake, or insufficient light reducing the conversion of calcium, a long-term low pH value, and excessively thick sludge at the bottom of the pond can all cause crayfish to develop soft shell disease. Excessive shrimp fry density and long-term feeding of a single type of bait can also lead to this disease.
Symptoms: The shrimp shell is soft and thin, the body color is not red, vitality is insufficient, mobility is poor, foraging is not vigorous, the shrimp refuses to eat, growth is slow, coordination is poor, and the shrimp shell is generally thin and relatively soft.
2. Hemorrhagic disease
Causes: Caused by Aeromonas bacteria.
Symptoms: The body surface of the diseased shrimp is covered with bleeding spots of varying sizes, especially obvious on the appendages and abdomen, the anus is red and swollen, and death follows shortly.
3. Shell rot disease
Causes: Caused by infection with Pseudomonas, Aeromonas, myxobacteria, Vibrio or Flavobacterium.
Symptoms: The shell of the diseased shrimp has obvious ulcerated spots, the spots are grayish white, and when the ulceration is severe they turn black, the spots sink in and holes appear, ultimately leading to internal infection and even death.
4. Black gill disease
Pathogen: The pathogen belongs to the Fungi Imperfecti among the fungi. This disease is caused by deterioration and pollution of pond water quality, which promotes the massive reproduction of Fusarium and its parasitism on the gill filaments, body wall, bases of the appendages or eyeballs of crayfish.
Symptoms: The gills change from flesh color to brown or dark brown, until they turn completely black, causing gill atrophy. Diseased shrimp often lie motionless at the pond bank, and finally die from breathing difficulty.
II. How Are Common Diseases in Crayfish Farming Prevented and Treated?
1. Prevention and treatment methods for soft shell disease
Remove sludge in winter.
Use quicklime to clear the pond, and after releasing the fry, splash 25 mg/L quicklime every 20 days.
Control stocking density; generally a pond shrimp quantity of two to three hundred jin per mu is best, and the density should not be too high.
The area of aquatic plants in the pond should not exceed 30% of the pond area.
Diversify the bait, appropriately increase calcium-containing bait, and when feeding the feed, increase the calcium content; for example, “Wangshenggai, Subu 100” and others can be added.
The suitable pH value for crayfish is between 6 and 8; try to maintain the pH value of the water body within this range. If the pH value is too low, quicklime can be used to adjust it.
2. Prevention and treatment methods for hemorrhagic disease
Maintain water color, do a good job of improving the bottom and regulating water, and normally pay attention to disinfecting with Huijindian and Yangzhian.
Regularly add Hongtikang to the feed.
Isolate diseased shrimp promptly when found, add Aifumie to the feed, and feed continuously for 3 to 5 days.
3. Prevention and treatment methods for shell rot disease
Operations during transportation and fry release should be meticulous; injured shrimp should not be put into the pond. Before the fry are put into the pond, they can be disinfected with 3% salt water for 5 minutes.
Handle operations carefully at ordinary times, and try not to injure the fry.
Keep the pond water clean.
Provide sufficient bait.
Every 15 to 20 days, splash the whole pond with quicklime dissolved in water at 25 g per cubic meter of water.
4. Prevention and treatment methods for black gill disease
First use Huidian 150 to 250 g per mu-m + Yangzhian 0.1 to 0.15 g per cubic meter of water to regulate water and improve the bottom, and use Shuihuangjin 0.3 to 0.5 L per mu to remove residual toxins. Then use Huijindian 45 to 75 mg per cubic meter of water + Aifumie 10 to 15 mg per kg of body weight.