This specimen resembled several others of around the same size and perhaps the same species, which were pretty common in my February sample from the upper Yakima. Unfortunately, I misplaced the specimen before I could get it under a microscope for a definitive ID.
Mysis shrimp also commonly known as opossum shrimp for the way they carry their broods, can be important to anglers as a curious bi-product of fisheries management practices. Fish and Game departments looking for a way to supplement the diets of planted kokanee salmon introduced these species from the Far North decades ago into many of the newly formed reservoirs. While not providing angling opportunities in the impoundments, they are often trapped in the dam's turbines and flushed down the tailwaters by the millions to feed the waiting trout. Their stunned or dead state makes them easy pickings. When these events occur the fish will really focus on them.
Mysida are not true shrimp and their appearance is unique. The species most commonly planted are virtually crystal clear transparant and they are more nymph shaped than shrimp shaped. Their legs are toward the front and they have a carapace that covers the head and thoracic segments. They also have appendages off the last abdominal segment that could be mistaken for tails. They have dark compound eyes.
Mysida Fly Fishing Tips
Mysis shrimp availability is hard to time so the angler fishing tailwaters below populations of these critters should always be prepared. Their clear bodies present special problems for the angler both in terms of imitation and detection. Over the years many successful patterns have been developed from complex to as simple as wrapping cellophane on a hook. The naturals are very difficult to see in the water though the fish don't seem to have this trouble.