Anisakiasis: This is a parasitic infection caused by the Anisakis worm, which is commonly found in raw or undercooked fish. The worm can attach to the intestinal wall, causing inflammation, bleeding, and diarrhea. The recent consumption of raw fish is a strong risk factor for this condition.

Vibrio vulnificus infection: This bacterial infection is associated with the consumption of raw or undercooked seafood, particularly oysters. However, it can also be found in other types of raw fish. Symptoms include diarrhea, which can be bloody, abdominal pain, and fever.
Pseudoterranovosis (formerly known as Anisakidosis or Cod worm disease): Similar to Anisakiasis, this condition is caused by another type of parasite found in fish. It can cause gastrointestinal symptoms including diarrhea, which may be bloody.
Food poisoning (other bacterial causes): Other bacteria like Salmonella, Shigella, or E. coli can cause food poisoning from contaminated fish, leading to symptoms including bloody diarrhea.

Intestinal perforation: Although less likely, if the parasitic infection (like Anisakiasis) or bacterial infection causes significant intestinal wall damage, it could lead to perforation, which is a medical emergency.
Septicemia: Certain bacterial infections from seafood, such as Vibrio vulnificus, can lead to septicemia, a potentially life-threatening condition.

Diphyllobothriasis: This is an infection caused by the fish tapeworm (Diphyllobothrium latum). While it primarily causes vitamin B12 deficiency and megaloblastic anemia, gastrointestinal symptoms can occur, though bloody diarrhea is less common.
Gnathostomiasis: A parasitic infection caused by the Gnathostoma worm, which can be found in raw or undercooked fish. It typically causes cutaneous or visceral larva migrans but can rarely cause gastrointestinal symptoms, including diarrhea.