A fish belonging to the order Cyprinodontiformes, which includes the family Poeciliidae of livebearers (commonly known for the guppy, molly, and other aquarium fish) and the family Cyprinodontidae of egg-layers (commonly known for killifish). This classification is currently under dispute; some ichthyologists place both families (and others) in the order Atheriniformes.

The term "toothcarp" comes from the presence of teeth in the jaws of these fish. True carp (and minnows), order Cyprinidae, have teeth only in their pharynx.