Keys to the Orders of U.S. Freshwater Fish
(Bony Fish)

Order names linked to a common name example.

1 a. Caudal fin heterocercal
b. Caudal fin not heterocercal
2
4
2 a. Caudal fin strongly heterocercal; mouth inferior; jaws almost or entirely toothless
b. Caudal fin abbreviated heterocercal, rounded behind; mouth terminal and bearing strong teeth
Acipenseriformes
3
3 a. Scales ganoid; dorsal fin short
b. Scales cycloid; dorsal fin long
Lepisosteiformes
Amiiformes
4 a. Skull asymmetrical, both eyes on same side of head
b. Skull symmetrical, eyes, if present, on opposite sides
Pleuronectiformes
5
5 a. Dorsal, caudal, and anal fins continuous
b. Dorsal, caudal, and anal fins separate
Anguilliformes
6
6 a. Body completely covered with dermal plates; snout elengated, tubular; anal fin redimentary or absent
b. Body scales or naked, never with dermal plates; snout never tubelike; anal fin present
Syngnathiformes
7
7 a. Body scaled or naked, but not with plates; head naked
b. Body scaled, or if naked, with few to many bony plates; head usually scaled
Cypriniformes
8
8 a. Spines in fins completely absent
b. Spines present in at least some fins (spines may be flexible or stiff, but not segmented)
9
12
9 a. Barbels absent
b. A single median chin barbel present
10
Gadiformes
10 a. Pectoral fins placed high on the sides, above the axis of the body
b. Pectoral fins placed near or much below the body axis
Beloniformes
11
11 a. Maxillae not forming border of upper jaw; jaw teeth conical in bands
b. Maxillae form part of the border of upper jaw; jaw teeth, if present, conical and never in bands
Cyprinodontiformes
Clupeiformes
12 a. Dorsal fin preceded by free spines (not connected by membranes)
b. Dorsal spines connected by membranes, to each other or to the soft dorsal fin
Gasterosteiformes
13
13 a. Pelvic fins abdominal or subabdominal; pectoral fins high on the sides, usually above body axis
b. Pelvic fins thoracic or nearly so; pectoral fins usually below body axis
Mugiliformes
14
14 a. Adipose fin present, or, if absent, the anus is far forward in the region of the isthmus
b. Adipose fin absent; anus in usual position just in front of anal fin
Percopsiformes
Perciformes

Order names and common name example:

Vertebrate Key