For recently stocked rainbow trout, nothing beats salmon eggs. If trout have been in a stream weeks or months, it's time to fly fish. But for the April weeks rainbows get stocked, fishing salmon eggs properly is a challenging, exciting, and rewarding exercise. Plenty of trout may be caught, but probably many more hits missed. Rainbows and salmon eggs are like sheepshead and sand fleas--both species bait stealers par excellence. But a salmon egg placed on a size 14 snelled hook (doesn't have to be a gold salmon egg hook) on two-pound test leader attached to a small snap tied to two-pound test spooled on the tiniest spinning reel you can find, seated on the shortest. lightest rod you have searched out, is game, no doubt about this; this is fun and something you will never feel you have mastered.
With my three-foot, six-inch ultra, ultra light rod I cast a single salmon egg with only a small snap for additional weight halfway across the North Branch Raritan. Compare the butt thickness to my thumb in the photo above. It is quite thin, thinner than the diameter of a salmon egg. The tip is so light I can bend it to the rod shaft. When I hook up, the fight of a ten-incher is strong and drag-screeching; it takes a while to bring the trout alongside my waders. I once landed an 18 1/2-inch brookie on this rod, foul hooked in the back near the tail. And you know how a fish advantaged like that fights.
Brookies take salmon eggs, but not as unhesitatingly as do rainbows.
For either fish, you need to practice, practice, practice at getting the eggs to drift right. (You will never hook every trout that striikes.) In deep, fast moving water you need to use some split shot or cylindrical weight such as the Boss Tin Stylers or Stix. But most situations call only for a snap; some demand that you add a piece or two of the swivels attached to the snaps, which you cut off from the snaps with nail clippers, only the snap leftover remaining whole. I keep what I cut by running a baby pin through the remaining loop of each swivel, then pin my vest. It's a small detail, but such a subtle difference--which gets a salmon egg in range of trout at the bottom of a faster moving run--can mean a fish or not.
http://littonsfishinglines.blogspot.com/2015/02/super-ultra-light-salmon-egg-spinning.html takes you to a more comprehensive article on the method.