ECOS Guide to the Ecology of the Northern Rockies

Name: Oncorhynchus Mykiss - Rainbow Trout

Family: Salmonidae (Trout and Salmon)

Order: Salmoniformes (Salmon/Trout/Pike)

Class: Osteichthyes (Bony Fishes)

Abundance:

Origin: Native to Kootenai River in northwest Montana, exotic everywhere else in Montana. Native range includes the majority of the west coast of North America into Alaska.

Active Season: Year Round

Size:

Colors:

General Description: Adults from 12” to 35”. Bluish to silvery grey with olive tints on back, side lighter and silvery with a reddish horizontal band, white to silvery underneath. In larger lakes tend to be more silvery all over body. Irregularly shaped black spots on back, side and head, also on dorsal, adipose and caudal fins. Small, terminal mouth. Small sharp teeth on jaws. Caudal fin slightly forked. Juveniles have distinct parr marks.

Similar Species: Westslope cutthroat trout (Oncorhynchus clarki lewisi) have spots that are concentrated towards the tail and tend to occur above the lateral line. Westslope cutthroat trout also have red throat slashes. Juveniles of rainbow trout and westslope cutthroat trout are difficult to distinguish. Hybrids between rainbow trout and westslope cutthroat trout are common and genetic analysis is required for positive identification because hybrids can look like westslope cutthroat trout, rainbow trout, or a mixture of the two.

Life History: Sexually mature in two or three years. Spawn in headwater regions of streams in the spring during high water. Juveniles hatch in early summer. Adults reside primarily in clear cold streams.

Distribution: Native range is in western North America and a small portion of northeastern Asia. Except for the Kootenai River, all Montana rainbow trout are exotic.

Habitat Description: Clear, cold streams and lakes

Feeding Habits: Feed primarily on juvenile and adult forms of aquatic insects (caddisflies, midges, stoneflies, mayflies). Adults may eat other fishes.

Did You Know: Rainbow trout are popular sport fish but are a major cause of the decline of native westslope cutthroat trout. Hybridization is common and often hybrid swarms are formed, where every fish in a population will have genes from both rainbow trout and westslope cutthroat trout. Rainbow trout in the Kootenai River are also called redband trout or interior rainbow trout. Steelhead are anadromous rainbow trout.

Glossary:

Adipose fin: a small fleshy fin along the midline of the back behind the dorsal fin.
Anadromous: migrate to the ocean but spawn in freshwater.
Caudal fin: tail fin.
Dorsal fin: a fin along the midline of the back, usually midway between the head and tail fin.
Lateral line: a line of pores along the fish’s side that open into an underlying sensory canal.
Parr marks: dark vertical blotches on sides of juveniles.
Terminal mouth: mouth located at the end of the head.

Keywords: Westslope, cutthroat, trout, Oncorhynchus

References:

Holton, G. D. and H. E. Johnson. 2003. A Field Guide to Montana Fishes, Third Edition. Montana Fish, Wildlife & Parks, Helena, MT.

Contributor:

Andrew Whiteley


Home Plant Guide Insect Guide Bird Guide Mammal Guide Geology Guide Fish Guide Fish by Name Fish by Family Fish by Order Glossary of Fish Terms Amphibian Guide Reptile Guide Habitats Descriptions Maps Contributors ECOS Home		Physical Characteristics - General Description - Similar Species - Life History - Distribution - Habitat - Feeding Habits - Did You Know - Glossary - References Name: Oncorhynchus Mykiss - Rainbow Trout Family: Salmonidae (Trout and Salmon) Order: Salmoniformes (Salmon/Trout/Pike) Class: Osteichthyes (Bony Fishes) Abundance: Origin: Native to Kootenai River in northwest Montana, exotic everywhere else in Montana. Native range includes the majority of the west coast of North America into Alaska. Active Season: Year Round Size: Colors: General Description: Adults from 12” to 35”. Bluish to silvery grey with olive tints on back, side lighter and silvery with a reddish horizontal band, white to silvery underneath. In larger lakes tend to be more silvery all over body. Irregularly shaped black spots on back, side and head, also on dorsal, adipose and caudal fins. Small, terminal mouth. Small sharp teeth on jaws. Caudal fin slightly forked. Juveniles have distinct parr marks. Similar Species: Westslope cutthroat trout (Oncorhynchus clarki lewisi) have spots that are concentrated towards the tail and tend to occur above the lateral line. Westslope cutthroat trout also have red throat slashes. Juveniles of rainbow trout and westslope cutthroat trout are difficult to distinguish. Hybrids between rainbow trout and westslope cutthroat trout are common and genetic analysis is required for positive identification because hybrids can look like westslope cutthroat trout, rainbow trout, or a mixture of the two. Life History: Sexually mature in two or three years. Spawn in headwater regions of streams in the spring during high water. Juveniles hatch in early summer. Adults reside primarily in clear cold streams. Distribution: Native range is in western North America and a small portion of northeastern Asia. Except for the Kootenai River, all Montana rainbow trout are exotic. Habitat Description: Clear, cold streams and lakes Feeding Habits: Feed primarily on juvenile and adult forms of aquatic insects (caddisflies, midges, stoneflies, mayflies). Adults may eat other fishes. Did You Know: Rainbow trout are popular sport fish but are a major cause of the decline of native westslope cutthroat trout. Hybridization is common and often hybrid swarms are formed, where every fish in a population will have genes from both rainbow trout and westslope cutthroat trout. Rainbow trout in the Kootenai River are also called redband trout or interior rainbow trout. Steelhead are anadromous rainbow trout. Glossary: Adipose fin: a small fleshy fin along the midline of the back behind the dorsal fin. Anadromous: migrate to the ocean but spawn in freshwater. Caudal fin: tail fin. Dorsal fin: a fin along the midline of the back, usually midway between the head and tail fin. Lateral line: a line of pores along the fish’s side that open into an underlying sensory canal. Parr marks: dark vertical blotches on sides of juveniles. Terminal mouth: mouth located at the end of the head. Keywords: Westslope, cutthroat, trout, Oncorhynchus References: Holton, G. D. and H. E. Johnson. 2003. A Field Guide to Montana Fishes, Third Edition. Montana Fish, Wildlife & Parks, Helena, MT. Contributor: Andrew Whiteley