Rainbow trout (Oncorhynchus mykiss) are widely distributed and sought-after sport fish globally, prized for their strength and adaptability. Understanding what they consume in their natural environment is fundamental to conservation efforts and successful angling. These fish are highly opportunistic feeders, meaning their diet constantly changes based on availability, habitat, and the time of year. Examining their natural feeding preferences provides necessary insight for locating and catching them.
Primary Components of the Wild Diet
The foundational diet of wild rainbow trout is dominated by aquatic macroinvertebrates, which are the larval and nymph stages of insects. Mayflies, caddisflies, and stoneflies are consumed throughout the year as they cling to submerged rocks and drift along the current. Trout selectively target the largest available individuals. These subsurface life stages represent the most consistent and calorically dense food source in most freshwater environments.
As trout grow, their diet expands to include larger prey items, particularly small baitfish like sculpins and minnows. Larger, trophy-sized trout often become more piscivorous, relying on other fish to meet their high-energy requirements. Crustaceans, such as scuds (amphipods) and crayfish, are also important components, especially in still water and slower-moving rivers where they are abundant.
Terrestrial insects that fall into the water from overhanging vegetation provide a significant seasonal protein boost for trout. Ants, beetles, grasshoppers, and crickets become readily available during warmer months, and trout will actively position themselves to intercept this surface drift. During spawning runs of other salmonid species, fish eggs become an extremely valuable food source. The high fat and protein content of eggs, especially salmon roe, allows trout to rapidly increase their energy reserves.
How Habitat and Season Influence Feeding
A rainbow trout’s environment dictates its food preference and feeding behavior, creating a distinct difference between river and lake populations. Trout in flowing water are primarily opportunistic drift feeders, positioning themselves to intercept food the current carries past them. Their diet leans heavily on aquatic insect nymphs and larvae, supplemented by terrestrial insects and annelids like worms washed in from the banks.
Conversely, trout living in still water, like lakes and reservoirs, rely more on a varied diet that includes plankton and bottom-dwelling organisms. These fish often cruise the deeper basins in search of cold, oxygen-rich water, where they prey on forage fish and larger crustaceans. Younger trout in lakes may sustain themselves largely on zooplankton and micro-invertebrates before graduating to larger prey.
Seasonal temperature fluctuations are the main driver of feeding intensity and location. Trout are most active and feed aggressively during the spring and fall, when water temperatures are in their optimal range, typically between 50°F and 60°F. During the summer, when water temperatures exceed 70°F, their metabolism slows down, forcing them to retreat to deeper, cooler water, which reduces feeding activity. In the winter, the trout’s metabolism slows significantly, and they feed much less frequently, often seeking out stable, deep water or focusing on subsurface nymphs and small fish.
Baits and Lures Used by Anglers
Anglers target rainbow trout using a variety of baits and lures designed to appeal to the fish’s opportunistic and selective feeding habits. Natural and processed baits are highly effective, often relying on scent and familiarity, especially for stocked fish. Live baits like worms or nightcrawlers provide natural movement and smell, mimicking an easy meal washed from the soil. Fish eggs, particularly salmon roe, imitate the high-value food source trout actively seek out during spawning seasons.
Processed baits, such as power dough and scented nuggets, are popular because they are infused with attractants like garlic or cheese and are often formulated to float off the bottom. These baits are particularly successful when targeting hatchery-raised trout, which are accustomed to a pellet-based diet and respond well to strong scents. Kernel corn and colored marshmallows are also used, mainly for stocked trout, as their bright colors and unique consistency can trigger a feeding response.
Artificial lures are designed to provoke an aggressive reaction by mimicking the appearance and movement of natural prey. Inline spinners use a rotating blade to create flash and vibration, simulating a distressed baitfish. Spoons flutter and wobble to imitate injured fish or larger insects, while small jigs with curly tails mimic aquatic larvae or minnows. Fly fishing utilizes three main categories of artificial flies: dry flies, nymphs, and streamers.