Order: Salmoniformes Family: Salmonidae Subfamily: Salmoninae
Foto: Lauri Urho
Description: The brook trout can be distinguished from other species of the family by the light stripy pattern on its dark back. Typical characteristics of the brook trout are the green or brownish back with its light, wormlike markings and the silvery white belly that becomes a bright orange red at spawning time. The dorsal and caudal fins have light, often yellowish, short stripes and spots. Like other charr, the brook trout has an adipose fin and white frontal borders on its ventral fins.
Origin and distribution: The lake trout (Salvelinus namaycush) and the brook trout diverged from their common ancestor during the Pliocene. The two species can still be crossed, and their hybrid is called a splake trout, which has been used in stockings to some extent. The brook trout originates in eastern North America. The species withstands and even requires cold water. Typical habitats are therefore spring-fed brooks and rivers, which are cold in summer but relatively warm in winter. The optimum temperature for an adult brook trout is 14−16°C. It tolerates acidic water better than European salmonids or rainbow trout. Natural stocks occur even in waters with pH 4.1. Being a popular species for sport fishing, the brook trout has been introduced into many areas around the globe. It was first imported into Finland back in the 1890s. Introductions got under way once again in 1965. Even though the results of these stockings were quite modest, reproductive stocks currently exist in brooks of northeastern and southern Finland and tributaries of the Kemijoki. The species occurs sparsely in Finland, but mainly in the north.
Diet, growth and migrations: Brook trout feed on larvae of water insects and other bottom fauna, zooplankton and small fish. Despite their diverse diet, they do not usually grow very large. In their original range, the biggest individuals of can weigh as much as 6 kg, but usually much less. In Finland, brook trout tend to be small, though they may attain a length of 30−40 cm and a weight close to 0.5 kg.
Reproduction: Brook trout spawn onto gravel bottoms in streams. The male reaches maturity at 2 years, the female a year later.
Fishing and catches: Stocking of brook trout, like that of rainbow trout, was intended primarily for sport fishing but stocking results have been quite modest. Rod fishermen praise the brook trout for its liveliness at the end of the line, and in some places brook trout have been introduced as catch-size fish.
Vulnerability, threats and management: The modest results of brook trout stockings have been attributed to badly chosen environments and domestication of the stock. On the other hand, when releases succeed, the brook trout can, as a new species, take over some area from the brown trout.