No matter what type of fish, a thin black membrane is tightly attached to the inner wall of its abdominal cavity. When preparing fish, this black membrane must be completely removed; otherwise, it is very likely to cause nausea, vomiting, and diarrhea after consumption.
This black membrane in the fish's abdomen serves to prevent various harmful substances from the internal organs from penetrating through the intestinal wall into the muscle. As a result, it naturally becomes a gathering place for bacteria, dirt, pesticides, and various other harmful substances.