Cutthroat trout, named for the distinct red-orange slash marks found under their lower jaws, are a fish species native to western North America. These adaptable fish inhabit a wide range of aquatic environments, from cold mountain streams to vast lakes. Their diet is notably varied, reflecting their opportunistic nature and ability to consume whatever prey is most available.
Primary Food Sources
The diet of cutthroat trout is primarily carnivorous. Insects form a significant portion of their food intake, encompassing both aquatic and terrestrial types. Aquatic insects, such as the larval and adult forms of caddisflies, mayflies, stoneflies, and midges, are consumed. Terrestrial insects like grasshoppers, beetles, ants, and caterpillars also become important food items when they land on the water’s surface, particularly during warmer months.
Beyond insects, cutthroat trout actively prey on smaller fish, including minnows, sculpins, and the fry of other fish species, even their own. Crustaceans are another staple, with items like scuds, amphipods, crayfish, and Mysis shrimp readily consumed where available. Other invertebrates such as leeches and worms are also eaten. While less common, small amphibians like frogs and salamanders, along with fish eggs, can be consumed, especially during spawning periods.
Dietary Adaptations and Variations
The diet of cutthroat trout is not static; it undergoes significant shifts influenced by environmental factors such as season, habitat, and the trout’s age and size. For instance, in summer, terrestrial insects become more prevalent, and trout feed more on grasshoppers and beetles. Conversely, during colder months, their diet shifts to focus more on aquatic larvae and nymphs, which are available year-round beneath the water’s surface. In spring, as water temperatures rise and insect hatches become more frequent, feeding increases.
Habitat also plays a role in dietary composition. Trout in lakes may consume more zooplankton and crustaceans, along with smaller baitfish. In contrast, river and stream-dwelling cutthroat trout primarily feed on a steady supply of stream-dwelling insects and their larval forms. Some subspecies exhibit highly specialized diets; for example, Yellowstone cutthroat trout are known to consume a large percentage of stoneflies, while other insects like mayflies and caddisflies make up the remainder of their diet.
A cutthroat trout’s diet also evolves as it grows. Younger trout, or fry, typically begin by feeding on small crustaceans and zooplankton. As they mature into fingerlings and juveniles, their diet expands to include small insects and a wider range of crustaceans. Larger, adult cutthroat trout can become more piscivorous, meaning they feed primarily on other fish, particularly in environments where baitfish are abundant.
Feeding Behavior
Cutthroat trout exhibit diverse feeding behaviors, allowing them to exploit various food sources. They often feed at the surface, readily rising to intercept terrestrial insects or emerging aquatic adults. This surface feeding is a common sight, especially during insect hatches. However, much of their feeding occurs beneath the water’s surface.
Underneath the water, cutthroat trout forage for nymphs, larvae, and small fish throughout the water column and near the bottom. They poke and prod along the substrate, dislodging insects attached to rocks or vegetation. While not strictly ambush predators, they can utilize cover such as logs or lily pads to wait for passing prey, darting out to capture it. Their keen eyesight is a primary sense used to locate and track prey, complemented by their lateral line system, which detects vibrations in the water, and a sense of smell that aids in identifying food items.