From ancient Greek μόνος - one + φαγεῖν - to eat, devour.

Monophage fish are fish that consume one type of food.

Extreme degree of specialization of nutrition in animals at the expense of only one single type of food, a type of stenophagy. It is opposed to omnivory.

Occurs among animal parasites - for example, the nematode Cystoopsis acipenseris parasitizes exclusively sterlet, and the salmonid Anchylodiscus siluri parasitizes only catfish. This type of feeding specialization is also characteristic of a number of crayfish.

Monophagy is predominantly observed in groups with a large number of species, especially in crustaceans and molluscs.