Egg Drift as a Hatch
You don't have to tell Alaskan trout fishers that their best hatches are not insect emergence of any kind, it is millions (billions or trillions?) of eggs emerging from spawning fish. Most of these egg laying fish are anadromous, meaning that they started their lives in fresh water, then migrated to sea where they consumed saltwater organisms and grew to adult size, then migrated back to fresh water to reproduce. In doing so they brought the ocean's bounty with them back to the rivers of their birth to fuel the life cycles of many unrelated plants, fish and insects.
In many river system, including most of the ones flowing into the Pacific Ocean the eggs from anadromoust fish contribute a large portion of the available protein consumed by resident trout during the late winter, spring and fall periods. In pounds of protein consumed by fish in rivers, fish eggs may rival and in some cases exceed insects as the dominant source.
In these same rivers fish also consume eggs from fish that never went to sea, including resident trout, char and whitefish. In some watersheds there is egg drift nearly year around. Predator fish can be highly selective to egg color and size which can vary greatly between spawning fish species. It pays to do a little research into fish egg size and color and be prepared to match the eggs drifting in your river.
If they are good enough for people, they are good enough for fish. Caviar = fish eggs! Fish eggs may be protein in the perfect natural package.
Once while fishing with an eminent aquatic biologist we watched an angler land several large trout using Glo Bugs. He commented that the guy wasn't really fly fishing,even though the Glo Bug was assembled using the same methods as the nymphs the biologist was using. My comment was, "Maybe he didn't enjoy catching five pound trout?"
How To Fish With Egg Flies