Pescetarians (or "pesco-vegetarians") are not really vegetarians. Although they don't eat red meat and poultry, they do eat fish and seafood (hence the "pesce", which is Latin for "fish"). Becoming a pesco-vegetarian is much better than being an omnivore, but if someone chooses this method, they should be aware that many fish have very high levels of mercury and other substances that can be harmful to humans.