Those on pescetarian or pollotarian diets may define meat only as mammalian flesh and may identify with vegetarianism. Most pescetarians maintain a lacto-ovo vegetarian diet with the addition of fish and shellfish, described as “pescatarian meal plan pdf but no other meat”. The common use association between such diets and vegetarianism has led groups such as the Vegetarian Society to state that diets containing these ingredients are not vegetarian.
A piscivore, a type of carnivore, subsists on a diet primarily of fish, whereas a pescetarian eats plant derivatives as well as fish. A similar term for the latter is “vegequarian”. The Merriam-Webster dictionary dates the origin of the term pescatarian to 1993 and defines it as: “one whose diet includes fish but no other meat”.
Some pescetarians adopt their diet because of the inefficiency of other meat sources. For example, in the United States most cattle, chickens and pork were not free-range and fed with grains specifically grown for their food. Therefore, the environmental impact and the amount of energy needed to feed a cow, a chicken or a pig greatly exceeds its nutritional value.
Such pescetarians might prefer to eat wild-caught fish, as opposed to farmed carnivorous fish that require food input of other fish. They might use guides such as the Seafood Watch to determine the sustainability of their seafood source. They argued that they have to eat “some kind of meat”, and fish is the least unethical meat source compared to chicken or mammals. Statisticians and others who have looked at animal consumption, however, suggest that fish and aquatic animals may be the least ethical food source among animal food sources, as many more fish are killed for the same amount of food relative to other animals, though this is purely in reference to the number of animals killed, as opposed to how the animals are treated while alive, or the environmental impact of pescetarian diet versus a general omnivore diet.