I don't know whether you keep sea crabs or river crabs, but whether you cut yourself is an act of animal protection. If you raise it well and have sufficient nutrition, it will grow back after a while. You can mash the shells of some clams (sea crabs) with meat or pork (river crabs) and feed them. You can put more water, change water frequently and live longer.

Don't tie your paws, he can't eat. When you tie them up, he will cut himself when he is frightened.