Brown trout are highly adaptable predators, known for their varied diet and opportunistic feeding behaviors. These fish consume a wide array of food sources. Their feeding strategy allows them to utilize whatever prey is most abundant and accessible in their habitat.
Aquatic Invertebrates and Other Small Organisms
A significant portion of a brown trout’s diet consists of aquatic invertebrates. Mayfly nymphs, caddisfly larvae, and stonefly nymphs are common food items, often eaten as they drift in the water column or reside on the riverbed. Trout will also feed on midges, tiny aquatic insects that can be present in large numbers.
Beyond insects, brown trout prey on other small aquatic organisms. Crustaceans like scuds, also known as freshwater shrimp, and sowbugs are important food sources. Crayfish and leeches also contribute to their diet, particularly for larger trout.
Terrestrial Insects and Small Vertebrates
Brown trout supplement their aquatic diet with food sources originating outside the water, such as terrestrial insects. Grasshoppers, crickets, beetles, ants, and cicadas are examples of land-dwelling insects that become opportunistic meals, especially during warmer months when insect activity is high.
As brown trout grow, their diet often expands to include larger prey. Small fish, such as minnows, sculpins, shad, and even juvenile trout, become important food items for mature individuals. They also consume amphibians like frogs and salamanders, and occasionally small mammals such as mice or voles that enter the water.
Factors Affecting Their Diet
Several environmental and biological factors influence what brown trout eat and when they feed. Seasonality plays a significant role, with food availability changing throughout the year; for instance, insect hatches are prominent during specific times, and summer often brings a wider variety of larger prey. Water conditions, including temperature and clarity, also impact prey activity and a trout’s ability to locate food.
The size and age of a brown trout directly correlate with shifts in its diet. Younger, smaller trout primarily consume larval insects and smaller invertebrates. As they mature, their diet diversifies, and they begin to incorporate larger prey, including fish, a transition known as piscivory. However, even large trout continue to opportunistically feed on smaller items. Habitat also dictates available food sources; for example, lake-dwelling brown trout may encounter different prey than those in fast-flowing rivers, which can influence their growth.