The Brook Trout, Salvelinus fontinalis, is a native cold-water fish species highly valued across North America, known for its preference for clean, cool, and well-oxygenated waters. Its diet is a direct reflection of its environment and life stage, making it an opportunistic feeder. The food sources consumed by this salmonid shift dramatically from microscopic organisms in its early life to larger, more calorie-dense prey as it grows and moves between stream and lake habitats. This adaptability is a key factor in the species’ survival across diverse aquatic ecosystems.
The First Meals: Diet of Brook Trout Fry and Juveniles
The diet of newly hatched Brook Trout, known as alevins or fry, is dictated by their small size and the need for easily digestible, abundant prey. Upon emerging from the gravel, the young fish begin external feeding, primarily consuming microscopic organisms found suspended in the water column. This initial diet is dominated by zooplankton, which are minute, free-floating animals like cladocerans, such as Daphnia, and copepods. As they grow into fingerlings, their diet quickly expands to include small aquatic insect larvae, particularly chironomids, commonly known as midges. These insect forms are abundant in the sediment and serve as a foundational, high-protein food source for the rapidly developing fish.
Primary Prey in Stream and River Environments
In the flowing waters of streams and rivers, the adult Brook Trout diet is focused on aquatic and terrestrial invertebrates delivered by the current. The bulk of their caloric intake comes from the larval and nymph stages of three major insect orders: Mayflies, Caddisflies, and Stoneflies. These aquatic forms, which spend up to a year or more on the stream bottom, are continuously dislodged and swept downstream, becoming readily available prey. The trout also rely heavily on “drift,” which refers to terrestrial insects that fall into the water from streamside vegetation. Ants, beetles, grasshoppers, and caterpillars can account for a significant portion of the diet, especially during the summer months when riparian insect activity is high. Additionally, small crustaceans, such as scuds or freshwater shrimp, are consumed, providing a consistent source of protein and fat near the stream bottom.
Specialized Diets in Lakes and Ponds
Brook Trout inhabiting the stable, standing waters of lakes and ponds often develop a diverse diet, including larger prey items. In these environments, the food web includes organisms rarely encountered in fast-moving streams. A major dietary shift occurs when they begin to prey on forage fish, such as minnows, sculpins, and other smaller species. Larger crustaceans, most notably crayfish, become a substantial food source for adult trout, especially during winter months. Leeches and aquatic worms are consumed opportunistically. In environments where they reach a large size, Brook Trout can exhibit cannibalism, preying on smaller members of their own species, or consume small vertebrates like amphibians or rodents that enter the water near the shore.
Feeding Strategies and Environmental Influence
Drift Feeding Strategy
Brook Trout are opportunistic feeders, expending the least amount of energy possible to obtain the maximum amount of food. Their primary feeding strategy in streams is “drift feeding,” where the trout hold a stationary position in the current, often behind a rock or log, and dart out to intercept invertebrates carried by the flow. This efficient method allows them to conserve energy while waiting for a constant supply of food.
Temperature and Activity
Water temperature is a dominant influence on their metabolism and feeding activity, as they are cold-blooded fish. Brook Trout feed most actively when water temperatures are in the optimal range, often between 50 to 60 degrees Fahrenheit. When water temperatures rise above 68 degrees Fahrenheit, their metabolism slows and feeding activity decreases sharply, sometimes ceasing entirely due to thermal stress. Feeding tends to be most active during the low-light hours of dawn and dusk, which is when many aquatic insects emerge and terrestrial insects are less visible, making them easier targets.