Causes of Rusty Spots on Crabs and Prevention and Treatment Methods

When rusty spots appear on the body surface of river crabs, brown and reddish-brown spots develop on the thoracic plate, dorsal carapace and walking legs, sometimes even appearing scorched, and white spots may also occur. These spots further expand and merge, forming black ulcers. In severe cases, the carapace is eroded into holes, which then leads to bacterial and fungal infection, seriously affecting the river crab's feeding and causing death.

The occurrence of this disease is mostly caused by deteriorated pond water quality, excessive heavy metal ions, or infection of wounds by certain Vibrio species capable of decomposing the chitin of the river crab's carapace.

Prevention and Treatment Methods for Rusty Spots on Crabs

1. Provide a good growing environment for river crabs. Pond clearing must be thorough, removing sludge, and quicklime should be used for pond clearing and disinfection. Normally, apply quicklime once every 15 to 20 days to keep the water clean.

2. Take care during transport, harvesting and rearing to prevent river crabs from being injured.

3. To treat diseased crabs, for an average water depth of 1 m, apply 0.5 to 1.5 kg of bleaching powder per mu by broadcasting over the whole pond, and at the same time feed the river crabs norfloxacin raw powder orally, adding 0.2 g of the drug per kg of feed, and feed continuously for 3 to 5 days.