Specific introduction:
1. If crabs live in fresh water, such as river crabs and hairy crabs, it is no problem to raise them in fresh water, and adding a little salt will not affect life. Bring back some seawater when you catch it. Tap water contains chlorine, which is poison to them, so it is useless to add salt.
2. Crabs belong to arthropods and breathe by filtering oxygen in water through gills. When eating crabs, there are a few spongy things on the front two sides under the lid. ) Crabs can survive for a period of time under humid conditions. But if they are dry for a long time, their gills will dry up and lose their breathing ability. Because they live by the sea for a long time, their gills adapt to high-salt seawater, but not to low-permeability fresh water. Crab death is mainly due to lack of oxygen, which leads to dyspnea. Although there is seawater, a little oxygen in seawater is not enough for it (and it may be placed in a sealed environment with seawater).