Opportunistic feeding occurs when there isn’t a preponderance of any particular aquatic organism and the fish are watching for and eating whatever comes along.
When fish are feeding opportunistically you don’t have to imitate the characteristics of a natural organism as you would during a hatch. This doesn’t mean it’s a good idea to fish a size 2, chartreuse Humming bird pattern. The fish is still looking for a recognizable food organism. It’s a good idea to turn over some rocks and run your net through some weeds. Get an idea of the size and coloration of the streams naturals. Use your observations to select a pattern, which looks natural to the trout. Patterns should be about the size and color of the naturals.
Sub-surface attractor patterns should stand out a bit from the color of the stream bottom. Patterns tied with marabou and soft hackles generate a lot of movement. They look alive. In a nutshell, the imitation has to look like a food organism. Outrageous patterns will spook wild fish, especially Browns. Bookies and Rainbows are attracted to some color.
One tip, especially in winter, Rainbows like color in the morning.
Trout are most active when water temperatures are between 55 and 70 degrees. Rainbows like temperatures between 60 and 70 degrees, Browns 50 to 65 and
Brookies from 55 to 60 degrees.
As the temperature goes up, oxygen goes down, feeding slows. Sudden cooling slows feeding.