Distribution

Rainbow trout are native to the Pacific Ocean and fresh waters of western North America. They naturally range from Mexico to Alaska and inland to the Rockies. However, they have been widely introduced throughout the world, and now occur across central North America to the eastern coast. Rainbow trout were first introduced to Atlantic Canada in the late 1800s. Today they are stocked in selected rivers and lakes throughout Nova Scotia and are known to reproduce in the Bras d'Or Lake watershed.

Physical Characteristics

Like most other members of the salmonid family, the appearance of rainbow trout varies.

• Adults in fresh water: colour varies from metallic blue to green or yellow-green to brown on the back, becoming silvery on the sides and light on the belly.
• Many small black spots cover the head, back, sides and fins, and spots on the tail are in obvious rows. The adipose fin (small fin in front of the tail on the back) has a black border. Mature fish have a distinctive rosy stripe along the side that extends from the gill cover to the caudal fin. Spawning fish have the colour shown in the painting above by Bruce Wood.
• Adults in saltwater: sea-run rainbow trout (steelhead) are more silvery in colour, may lack the rosy stripe, and show less spotting on the sides.
• Young rainbow trout (parr): have 5 to 13 well-spaced dark part marks on the sides and show less spotting on the body than adults.
• Rainbow trout may look very similar to Atlantic salmon and brown trout, but can be distinguished by the regular rows of spots on the tail, the lack of any coloured spots and the absence of red in the adipose fin.
• Rainbow trout can grow as big as 25.8 kg (57 lb) but in Nova Scotia usually grow up to 2.7 kg (6 lb).

The largest rainbow trout was caught in Alaska in 1970 and weighed 19. 1 kg (42 lb). The Canadian record was caught in British Columbia in 1976, and weighed 35.12 lb.

The rainbow trout is commonly used as a laboratory animal for water quality testing.

Natural History

Different populations of rainbow trout may have very different life history patterns. Rainbow trout may live in lakes or ponds, they may be stream dwellers or they may be anadromous, spending part of their lives at sea before returning to freshwater to reproduce. They prefer water temperatures of 12 to 18øC and do well in clear, cool, deep lakes or cool, clear, moderately-flowing streams with abundant cover and deep pools. They spawn in the spring (usually from March to May in Atlantic Canada) in small tributaries of rivers, or in inlets or outlets of lakes. Spawning can also take place in late fall or early winter. Rainbow trout usually return to the streams where they hatched.

Spawning occurs in shallow riffles with gravel bottoms. The female uses her body to dig a nest (redd) in the gravel. One or two males will spawn with her in the nest, then she buries the fertilized eggs. She repeats this process until all her eggs are laid. Most female rainbow trout produce about 1,000 to 4,000 eggs.

The eggs are 3 to 5 mm in diameter and hatch in 4 to 7 weeks depending on the temperature. In another 3 to 7 days the young absorb the yolk sac and emerge from the gravel.

The young of lake-dwelling fish may move into the lake by the end of their first summer. Some stay in a tributary up to 3 years before entering the lake. Young rainbow trout seek cover and prefer slow-moving shallow stream areas where rubble, rocks, instream debris and undercut banks provide shelter. Older trout move into faster and deeper stream waters.

Rainbow trout that migrate to sea (steelhead) spend from 1 to 4 years in freshwater before they transform into smolts to prepare for life in salt water. Rainbow trout smolts lose their parr markings and become silvery. They migrate to sea in spring and remain there for a few months to several years before they return to freshwater.

Rainbow trout take a wide variety of foods, but in freshwater they eat mainly insects, crustaceans, snails, leeches, and other fish if available. At sea they eat mainly fish, crustaceans, and squid.

Rainbow trout growth varies widely depending on their habitat, diet, and life history pattern. Generally fish that go to sea or live in large productive lakes, grow largest and live longer. Rainbow trout usually mature at ages 3 to 5, at sizes that range 15 to 40 cm (6 to 16 in) long. Many will spawn repeatedly. Rainbow trout can live to 11 years.

Published With Funding from the Canada-Nova Scotia Cooperation Agreement on Economic Diversification, Resource Competitiveness Program.