What do trout eat? - Part 1

The list of things found inside trout, or seen eaten by trout, is long. Small baitfish, ants, spiders, cock-a-bullies, nymphs, larvae, cicadas, dragonflies, grasshoppers, moths, butterflies, bees, wasps, mice, frogs, crayfish, shrimps, other trout, other fish, eels, worms, maggots, trout eggs, chicken bones, bread, cigarette butts, tear-tabs from drink cans, and many more.

If you took a quick look at all these things trout could eat you may be tricked into thinking that they could be tempted with just about anything thrown into the water. And over the long run they probably can, but on any one day they can be as finicky as a 2 year old child about what they will and won’t eat, and even quicker at tossing it back at you.

80% Of The Time Most Trout Eat Nymphs or Larvae

In rivers, streams, and most lakes, the principle diet of any trout is the nymph or larvae form of insects. Most aquatic insects spend most of their lives as nymphs or larvae under-water, before emerging as winged insects to breed. Many of these insects spend only days in their winged form, but can spend years in their nymph form. On most water, the fishermen who can best exploit the knowledge of how trout and perhaps more importantly, where trout feed on nymphs, will achieve the most success.

Mayfly nymph illustration

The simplistic difference between nymphs and larvae, is that nymphs tend to look like the winged adult and have wing cases. Larvae do not look like the adult and have no wing case (a caddis is a good example.)

For the rest of this book I will use the term 'nymph' to cover both nymphs and larvae, except where the distinction is important.

Nymphs in Rivers and Streams

Nymphs live throughout rivers and streams, from bank to bank, from the deepest to the shallowest water. Some live under and on rocks. Others burrow into mud and silt. Still others cling to weed. But all of them, no matter where they live, share some common characteristics.

The two characteristics that most interest trout and fishermen are:

  • In order to breed, these nymphs must come to the surface for their metamorphosis into insects, and this means leaving the safety of the rock, mud or weed, and floating up to the surface at the mercy of the currents, or crawling onto dry riverbanks, rocks or fallen tree branches.
  • When moving from one source of feed to another, many nymphs lose hold and float away in that current.

Dragon-Fly Fly
A fly tied to represent a
Dragon Fly Nymph

Armed with this knowledge it is a small mind-jump to work out that anywhere that currents are concentrated or deflected will concentrate floating nymphs, in a veritable smorgasbord of passing feed.

In strong currents, such as in riffles or rapids, a trout would find it difficult to stay feeding in the strong current. They hover in the lee of obstructions such as rocks or logs and only have to move a very short way, often just a turn of the head, to pluck feed out of the current.

Remember that all predators, fish included, cannot expend more energy catching their prey, than the energy provided by that prey. Otherwise they will soon die.

Nymphs in Pools and Lakes

dragon fly nymph
A Dragon Fly nymph

In pools and lakes many insects crawl along the bottom and onto the shore to hatch. Trout patrol the shallows intercepting the nymphs. Other nymphs, and some worms, emerge from the mud and silt on the bottom to float to the surface. Trout intercept these nymphs on the journey. Other nymphs crawl up weed towards the surface and trout will pluck these nymphs from the weed.

The important point here is that in the absence of significant current, trout can move freely to feed, and because nymphs move slowly, so can the trout. They can expend little energy chasing food.

Observing trout feeding this way will soon reveal a regular ‘patrol pattern’. The trout will patrol a quite finite path.

What Do Trout Eat? - [Part 2]

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