Food Preferences of the Rainbow Trout

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Food Preferences of the Rainbow Trout

by Ron Newman

Do Rainbow Trout have a 'preference' for one food item on the aquatic menu over something else? You're darn right they do. At the best of times the trout are fussy about what and when they eat. Even when they are feeding, they seem to have some form of communal communication that allows them to determine "OK everybody, lets eat Chironomid this afternoon".

These communal feeding habits tend to indicate that there is a systematic logic as to how the trout feed. There seems to be more to it than just "Oh, there is a Chironomid and I think I shall eat it". The trout, as a group, seem to have a definite 'preference' for one food item over another. Sure, there will be an occasional trout that varies from the communal norm but feeding is fairly consistent throughout the trout population in a lake.

I have been looking for, and think I have found 'some' of the rules governing feeding among the Rainbow Trout. The food of choice will vary with the season, time of day, and various environmental conditions conducive to feeding on that food source.

Rainbow Trout

Seasonal Food Preferences

That old saying "Match the Hatch" may be responsible for more fish NOT being caught than any other factor in the selection of what fly to use. Many fly fishers will think I'm being Sacrilegious by questioning this most basic statement from the Gods of Fly-Fishing. "Match the Hatch" isn't totally wrong as much as it isn't totally correct. This is because Rainbow Trout 'prefer' certain foods at certain times and that preference may not be the main hatch being observed.

A more correct statement would be to "Match the NEW Hatch". Trout prefer food items that are just becoming available during the season. Trout feeding throughout May, for example, will have already gorged themselves on Chironomid hatches. The trout then go into a 'non-feeding' cycle to digest their food. When the trout are ready to resume feeding, they probably don't want to see or eat another Chironomid. After a full diet of Chironomid, the trout will "prefer" another, any other, food source. When Caddis, Damsels, or another food source FIRST becomes available in June, it will be the food of choice even though there may be many Chironomids still available and hatching. Naturally, if these other food sources are not available the trout will try a smaller new food or even revert back to the Chironomid.

Also, the trout will generally pick the larger of two new items on the menu. If two hatches of Chironomid are just starting, and one species is significantly larger than the other, it will probably be the preferred food even though substantially fewer individuals are hatching. The fly fisher can take advantage of this knowledge.

Daily Food Preference

One of the most profound examples of preference is to watch a 'feeding change' that occurs within a short period of time. I have watched trout switch from Chironomid to Caddis, for example, within an hour. The fish were actively feeding on Chironomid in the morning. At 11:00am, the bite stopped, at 11:30 I saw a single Caddis emerge, and by noon I was into better fishing than the morning hours with a Caddis pupa. Virtually every fish in the lake had switched from abundantly available Chironomid to the scarce Caddis.

All the fish seemed to know that Caddis were going to be available and all agreed that they were to be the afternoon food of choice. Bugs often hatch according to water temperature, sun-angle, and hours of daylight. Trout seem to know when conditions are right for certain hatches. In this case it was almost as if the morning Chironomid feed was just an appetizer before the main course.

There is also a preference for certain aquatic bugs at certain times of the day. Often this is because of availability. For example, dragonfly hatches occur at night and the trout are most likely to feed on them at that time. However, damselfly hatches occur in the afternoon and that is the prime time for feeding on those. The time of day is an important consideration for the fly fisher trying to determine what fly is likely to be best. But again, the beginning of a hatch is far better than the middle. And the middle of a hatch is far better than the end.

Environmental Limiting Factors

Environmental factors affect the trout's preference for a newly available food source. When conditions are right they will be 'right on' a new food source. If conditions are wrong, they will wait until conditions are more favorable to feed on their food of choice.

For example, bright sunlight with calm conditions will drive trout into deeper waters. The fish will leave the shallows even though a new hatch may be just beginning. The fish will then wait to feed or they may seek a preferred food available within the deeper waters. If a breeze picks up and the light levels drop the trout will move back to the shallows and resume feeding on what they had earlier left. Either way, it will still be something they haven't been consuming in vast quantities over the last little while. Trout will sometimes risk unfavorable conditions to get a preferred food but it is not the general rule-of-thumb. Also, it is usually the smaller fish that take these risks.

Fishing Tips

  • Fish the NEW food sources (daily or seasonal) under favorable lighting and environmental conditions. Remember that these preferred foods are not always easily observed.
  • If two new foods become available at about the same time, odds are that the trout will prefer the larger of the two.

So keep up with the times. 'Match the New Hatch' and improve your success. This formula can turn a mediocre day of fishing into an excellent day of fishing.

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Back In My Day
Things I Have Learned
Entomology Articles
Rainbow Feeding Habits
The Aquatic Menu
Game Fish
Kamloops Trout
The Extraordinary Rainbow
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Caddisflies (Sedge)
Gammarus Shrimp
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Food Preferences of the Rainbow Trout