From the Greek στενός, "narrow, limited" and φᾰγεῖν, "to eat, devour".
Stenophages are aquatic organisms whose food spectrum consists of a small number of prey items.
The biological advantage of stenophagy is efficient use of few food species due to good adaptation to them. It creates isolation with species close in food regime, but in case of change of habitat conditions leads to threat of extinction or to sharp fluctuations in numbers (its deficiency).
An example is black amur, which feeds on shellfish.