Does my dad have to have fever in order to have the stomach flu?

No: Fever may occur, but is not always there with stomach infections.

Not necessarily: Gastroenteritis symptoms may include: diarrhea , nausea, vomiting, abdominal cramps/pain, headaches, muscular aches & pains as well as fever (low grade). Bloody stools are not usually associated with gastroenteritis. According to the CDC, viral gastroenteritis usually has a duration of 1 to 10 days (depending on the specific virus). The average is 1 to 3 days.