No matter what kind of fish, a thin layer of black film adheres to the inner wall of their abdominal cavity. When people are cooking fish, this layer of black film must be removed, otherwise it can easily cause nausea, vomiting, and diarrhea after eating.
This layer of black membrane plays a role in preventing the penetration of various harmful substances in the internal organs of fish through the intestinal wall into the muscles inside the fish's abdomen, so it naturally becomes a gathering place for bacteria, dirt, pesticides and other harmful substances. .