Why do crabs foam?

When we buy crab, we have to choose live crab with hard shell, release a lot of white foam. What is the rule of this?

Crab is a crustacean living in the water, it is like a fish, also using gills to breathe. But the gills of the crabs and the gills of the fish are not the same, and do not grow on either side of the head, but rather because many of the soft, spongy, gill-like gill joints form on the upper sides of the body. by hard shell.

Crab bearing stores a lot of water.

When the crab lives in the water, from the pincers and the root part draws clean water (dissolved oxygen in the water will enter the blood of the capillary gills), after running through the gill is released by the senses on either side of the mouth. .

Although crabs usually live in water, they are different from fishes, they often crawl upland to find food, and after leaving the water, it will not die. This is because the gills of the crab store a lot of water , when leaving the water is still like in the water, can also not stop breathing, inhaling a large amount of air, released by the senses on the sides of the mouth.

Because the air that it inhales too much, the contact area between gill and air is relatively large, the content of water and air in the gill contains water that has formed countless bubbles , increasing day by day. many, so the front of the mouth extruded into a lot of white foam .

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