Mergus is the genus of the typical mergansers fish-eating ducks in the subfamily Anatinae. The genus name is a Latin word used by Pliny the Elder and other Roman authors to refer to an unspecified waterbird.

A piscivore is a carnivorous animal that primarily eats fish. The name piscivore is derived from Latin piscis 'fish', and vorō 'to devour'. Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evolution ; insectivory came next; then in time, the more terrestrially adapted reptiles and synapsids evolved herbivory.