1, a catty of green crabs should be steamed for 21 minutes.

2. The blue crab, a genus of Portunus, is a burrowing aquatic crustacean, inhabiting mud beaches, mangroves and other places in the intertidal zone. It is often eaten as a delicacy with tender meat, delicious taste and rich nutrition. The blue crab is salty and cold in nature, and enters the liver and spleen meridians, which has the effects of promoting blood circulation, removing blood stasis, clearing away heat and supplementing nutrition.