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Fast Facts: Rainbow trout

Scientific name: Oncorhynchus mykiss
Average weight: 1 to 7 kg but can reach up to 9 kg
Average length: 30 to 75 cm but can reach up to 90 cm
Average lifespan: 4 to 6 years (in the wild)

Did you know?

The rainbow trout is a member of the salmon family and can get quite hefty. The largest recorded rainbow trout was 25.8 kilograms!


A rainbow trout has a long, skinny body and can come in a variety of colours from brown and black to olive and blue-green. No matter the colour, the rainbow trout always has a reddish stripe length-wise down both sides of its body. The fish’s underbelly is white and tiny black spots cover its back, sides and fins.

The rainbow trout actually has seven fins in total: a pair of pectoral fins, a pair of pelvic fins, an anal fin, a dorsal fin and an adipose fin. To distinguish wild rainbow trout from the hatchery kind, fish hatched and raised in captivity and then released into the wild, oftentimes the adipose fin will be clipped in the hatchery variety.

The fish has sharp teeth on the roof of its mouth but has no lower teeth at all.


Rainbow trout are carnivores that won’t eat any vegetation growing in the water. Insects, leeches, small fish, crayfish and mussels are just a few delicious treats a rainbow trout likes to munch on.

This fish likes to live in cool freshwater but some of them migrate into saltwater and become steelhead trout. Steelheads are the same as rainbow trout except in saltwater, the fish gets bigger, eats larger prey and has to return to its birthplace to spawn, much like a salmon. However, the freshwater rainbow trout does not have to migrate back to its birthplace to lay its eggs.

To lay her eggs, a female rainbow trout must dig a nest in the gravel at the bottom of the body of water. To build this nest, called a red, the female turns her body to the side and flaps her tail, creating a depression in the gravel. She then lays up to thousands of eggs in multiple redds. As she is doing this, one or more male rainbow trout fertilize the eggs with something called milt.


The rainbow trout is native to lakes and rivers in North America west of the Rocky Mountains. However, it has been introduced to bodies of water all over the world because of its popularity as a sporting fish.

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