How to prevent and treat common diseases in river crab farming
I. Shell ulcer disease
1. Symptoms: Ulcerative lesions occur on the crab's exoskeleton. In the early stage, there are many brown spots on the shell, with each spot having a slightly reddish depressed center. In the late stage, the edges of the spots turn black, the ulcers in the center deepen, and the shell is eroded into holes, exposing muscle or membrane, ultimately leading to the death of the river crab.
2. Prevention and treatment methods: (1) Try to avoid injuring the crab's body. (2) Keep the water clean and fresh, and ensure the pond bottom has about 10 cm of soft mud. (3) Splash the entire pond with a 15×10E-6 concentration of quicklime solution or a 1×10E-6 concentration of furazolidone solution. Splash once every 7 to 10 days, for 2 to 3 consecutive times. (4) Mix 0.1 to 0.2 g of oxytetracycline or erythromycin per kg of crab body weight into the bait and feed for 7 to 10 days.
II. Black gill disease
1. Symptoms: The main site of infection is the gills. In mild cases, part of the gill filaments appear dark gray or black; in severe cases, all gill filaments turn black. Diseased crabs move slowly and have difficulty breathing.
2. Prevention and treatment methods: (1) Remove leftover bait every day, replace stagnant water in time, and remove diseased crabs; (2) For prevention, splash quicklime solution over the entire pond at a concentration of 15×10E-6 to 20×10E-6. (3) For treatment, splash quicklime solution continuously 2 to 3 times at a concentration of 20×10E-6. (4) Diseased crabs can be placed in a 2×10E-6 to 3×10E-6 concentration of furanone solution and soaked 3 to 4 times, about 20 minutes each time.
III. Edema disease
1. Symptoms: The diseased crab's abdominal flap and the lower part of the back shell become swollen and translucent, and it refuses to eat, leading to death.
2. Prevention and treatment methods: (1) During the farming process, minimize disturbance to them. (2) Frequently add fresh water, and feed more live bait and fresh vegetable leaves. (3) To treat this disease, splash a 0.5×10E-6 to 1×10E-6 concentration of oxytetracycline solution or furazolidone solution over the entire pond, or splash a 0.1×10E-6 to 0.2×10E-6 concentration of furazolidone solution over the entire pond.
IV. Ciliate disease
1. Symptoms: In the early stage, many yellow-green or brown fluffy substances grow on the crab's body surface. It moves slowly, its antennae are insensitive, its body surface and appendages feel greasy, and microscopic examination shows many ciliate parasites attached.
2. Prevention and treatment methods: (1) Thoroughly clear the pond with quicklime before stocking. (2) Before stocking seedlings, soak them in a 20×10E-6 concentration of zinc sulfate solution for 1 hour. (3) For treatment, splash a 3×10E-6 concentration of zinc sulfate over the entire pond.