What Do Trout Eat? A Comprehensive Guide to Their Diet
Trout are opportunistic feeders, consuming a wide variety of aquatic and terrestrial insects, crustaceans, and even smaller fish. Their diet depends heavily on factors like season, location, and age, but primarily consists of insects in their larval and adult forms.
Understanding Trout Diet: A Foundation
Trout are fascinating creatures, and understanding their diet is crucial for both anglers and anyone interested in freshwater ecology. Their food sources are incredibly diverse, reflecting the health and biodiversity of their environment. By examining what they eat, we can better understand their habitat requirements and the overall health of the ecosystem they inhabit. Their feeding habits also influence their behavior, making knowledge of their diet essential for successful fly fishing.
The Building Blocks: Primary Food Sources
Trout diets are influenced by a range of organisms. While the specific composition varies, certain food sources are consistently important:
Aquatic Insects: These form the cornerstone of the trout diet. Mayflies, caddisflies, stoneflies, midges, and various other aquatic insects are crucial, particularly in their larval (nymph or pupa) and adult forms. The emergence of these insects often triggers intense feeding activity.
Terrestrial Insects: Insects that fall into the water from surrounding vegetation also contribute significantly. Grasshoppers, ants, beetles, and caterpillars are examples of terrestrial insects that provide a substantial meal.
Crustaceans: Smaller crustaceans, such as scuds (amphipods) and freshwater shrimp, are important in some habitats, providing a readily available source of protein and nutrients.
Smaller Fish: Larger trout, especially brown trout and lake trout, often become predatory and consume smaller fish, including minnows, sculpins, and even smaller trout. This is a key stage of their development for those larger species.
Other Invertebrates: Worms, snails, and other aquatic invertebrates contribute to the diet, although generally to a lesser extent than insects and crustaceans.
Seasonal Variations in Trout Diet
A trout’s diet changes considerably throughout the year, reflecting the availability of different food sources.
| Season | Primary Food Sources |
|---|---|
| Spring | Mayfly hatches, emerging caddisflies, stoneflies, worms dislodged by runoff |
| Summer | Terrestrial insects (grasshoppers, ants), smaller fish, caddisflies, mayflies |
| Fall | Spawning insects (attracts fish feeding), terrestrials, smaller fish, crustaceans |
| Winter | Midges, small nymphs, crustaceans, scuds |
Location, Location, Location: Habitat Influences
The specific habitat that trout occupy plays a major role in defining what they eat. Stream trout in rocky streams have different diets than lake trout in deep, still waters. The presence of certain insect species, crustaceans, or fish will dictate the dominant components of their diet. For example, tailwater fisheries often have abundant scuds, making them a primary food source for trout in those environments.
Age and Size: A Matter of Scale
A trout’s size directly influences the size and type of prey it can consume. Smaller trout rely more heavily on smaller insects and crustaceans, while larger trout graduate to larger insects, crustaceans, and ultimately, smaller fish. This transition reflects the energetic demands of a larger body and the ability to handle larger prey.
The Art of Matching the Hatch: Fly Fishing Implications
Understanding a trout’s diet is the cornerstone of successful fly fishing. “Matching the hatch,” or selecting flies that imitate the insects that trout are actively feeding on, is a critical skill. Anglers carefully observe insect activity, water conditions, and trout behavior to choose the most effective fly pattern. Knowing what a trout eats helps anglers to better understand their quarry, the insects they eat, and the habitats they inhabit.
Common Mistakes and Misconceptions
Assuming Trout Only Eat Flies: Many believe that trout only eat insects or “flies.” This is a misunderstanding; trout are opportunistic feeders and consume whatever is readily available and nutritious.
Ignoring Terrestrials: Focusing solely on aquatic insects and ignoring terrestrial insects is a common mistake, especially in the summer and fall. Trout often target terrestrial insects that fall into the water, providing a readily available and substantial meal.
Overlooking Crustaceans: In certain habitats, especially tailwaters, crustaceans like scuds are a primary food source and should not be overlooked.
Frequently Asked Questions (FAQs)
What is the difference between a mayfly nymph and a mayfly dun?
A mayfly nymph is the aquatic larval stage of the mayfly, living underwater. A mayfly dun is the first adult stage that emerges from the water. Dun are often darker in color than their nymphal stage.
Are trout cannibalistic?
Yes, larger trout will sometimes eat smaller trout. This is more common among brown trout and lake trout, especially when food is scarce.
How often do trout eat?
Trout feed more actively during warmer months and in the early morning or late evening. They eat almost constantly when food is plentiful, but slow down during the cold winter months.
Do trout eat plants?
Trout generally do not eat plants directly. However, they may consume plants accidentally while feeding on insects or other organisms associated with aquatic vegetation.
What are midges, and why are they important to trout?
Midges are small, two-winged flies that are incredibly abundant in many trout streams and lakes. They are an important winter food source for trout when other insects are less active.
How can I tell what trout are eating in a particular stream?
Observe the insect activity near the water, examine the stomach contents of caught fish (if legally permissible and ethically done), and use a kick net to sample the aquatic insects living in the streambed.
Do different species of trout have different diets?
Yes, while their diets overlap, different species of trout may show preferences for certain food sources. For example, lake trout tend to consume more fish than rainbow trout. Brook trout tend to feed on what is most easily accessible.
What is a ‘hatch’ in fly fishing terms?
A “hatch” refers to the emergence of aquatic insects, particularly mayflies, caddisflies, and stoneflies, from their larval stage to their adult stage. Hatches often trigger intense feeding activity in trout.
Do trout eat worms?
Yes, trout will eat worms, especially after heavy rain when worms are washed into the stream.
Are there any insects that trout refuse to eat?
While trout are opportunistic feeders, they generally avoid insects that are toxic or unpalatable.
How does water clarity affect a trout’s diet?
In clear water, trout can see farther and are more selective in their feeding. In turbid water, they may rely more on opportunistic feeding and consume whatever is readily available.
What is the best way to imitate terrestrial insects when fly fishing?
Use fly patterns that resemble common terrestrial insects like ants, beetles, and grasshoppers. Drift your fly along the bank or near overhanging vegetation to simulate a natural fall into the water. Pay attention to the size and color of the natural terrestrials present.