Brown Trout, Salmo trutta

The Brown Trout (Salmo trutta) is originally a European species of salmonid fish. It includes both purely freshwater populations, referred to Salmo trutta morpha fario and S. trutta morpha lacustris, and anadromous forms referred to as the sea trout, S. trutta morpha trutta. The latter migrates to the oceans for the majority of its life and returns to freshwater only to spawn. The specific handle trutta comes from the Latin trutta, meaning, literally, “trout”.

The lacustrine morph of the brown trout is most normally potamodromous, migrating from lakes into rivers or streams to spawn, although evidence signifies stocks spawn on wind-swept shorelines of lakes. S. trutta morpha fario creates stream-resident populations, usually in alpine streams, but occasionally in larger rivers. Anadromous and nonanadromous morphs coexisting in the same river seem to not be genetically distinct. What determines whether they migrate or not remains unknown.

It is normally considered to be native to Europe, but the natural distribution of the migratory forms may in fact be circumpolar. Landlocked populations also take place far from the oceans, for example, in Greece and Estonia.

The brown trout is a medium sized fish, growing to 20 kilograms or more and a length of about 100 centimeters within some localities, although in many smaller rivers, a mature weight of 2 pounds or less is very common. Salmo trutta lacustris achieves an average length of 16 to 32 inches with a maximum length of 55 inches and about 60 pounds. The spawning behavior of the brown trout is much like that of the closely related Atlantic salmon. A typical female produces about 900 eggs per pound of body weight at spawning.

These trout can live to ages of 20 years. But as with the Atlantic salmon, a high proportion of males die after they spawn, and most likely fewer than 20 percent of anadromous female kelts recover from spawning. The migratory forms grow to significantly larger size for their age because of the abundant forage fish in the waters where they spend the majority of their lives. Sea trout are more commonly female in less nutrient rich waters. Brown trout are active both by day and by night and are opportunistic feeders. While in freshwater, their diet consists of invertebrates, other fish, frogs, mice, birds, and insects. Freshwater brown trout can range in color from largely silver with few spots and a white belly to the more well-known brassy brown cast fading to creamy white on the fish’s belly, with medium sized spots surrounded by lighter colored haloes.

Image Caption: Brown Trout (Salmo trutta fario). Credit: U.S. Fish & Wildlife Service/Wikipedia