MYSIS shrimp Guide Brian Byerly of Lakewood, Colorado, displays a Mysis shrimp-fed rainbow caught on the Taylor River near Gunnison. Byerly used a #20 Barr Emerger and a 5X tippet to land the 34-inch long fish, which weighed 22 pounds and had a 23-inch girth. DAN WRIGHT Colorado Hogs | Reudi Reservoir & Frying Pan River | Lake Dillon & The Blue River | Taylor Reservoir & River | Mysis Tactics | Leaders & Tackle | Mysis Relicta | Fly Shops It is late October and the big fish in the tailwater just below the dam make sounds like bricks dropping into the river. The sounds jolt the quiet morning every six or seven minutes. No bugs are hatching. Those summer days are long past, and the fish (rainbows up to ten pounds) won't take anything on the surface. They are taking something just under it, and when they turn abruptly, their tails pop out and slap hard on the water. My companion informs me that they are feeding on Mysis relicta, a.k.a. Mysis "shrimp," a crustacean known to fatten fish in tailwaters below Western reservoirs where the conditions are right. Of the more than 50 reservoirs where Mysis live in the Western U.S. and Canada, only three have the depth, water temperature, and dam construction characteristics (namely, outtake tubes that draw water from the cold bottom where the Mysis live, rather than the middle) that result in large numbers of Mysis being swept into their associated tailwaters. All are in Colorado. They are Reudi Reservoir, Dillon Lake, and Taylor Reservoir. Below each dam, you can find the true hogs, fish that look like footballs (if they made footballs that big). The fish grow large on Mysis shrimp, but they will take a variety of flies--even dry flies--under the right circumstances. Big Tailwater Trout Mysis create big trout in tailwaters for several reasons. Most noteworthy is the high nutrient level of Mysis--much higher than that found in midge larvae or Baetis nymphs. Mysis are a "high-fat," high-energy mouthful for trout. Mysis-fed trout not only grow large, they often exhibit some of the most brilliant colorations for their species. Rainbows (left) have brilliant red stripes, and browns (above) often have reddish-orange tails and bright red spots. Also, trout in these tailwaters don't need to work hard to get a mouthful of Mysis. Most of the shrimp are dead or near dead by the time they reach the river, so trout can easily grab them. Mysis are accustomed to slow movements in cold, dark places--not the clear water and relatively drastic conditions of rushing through a pipe in a dam and splashing into a tailwater. By the time the Mysis reach the tailwater, most of them have died and turned from a translucent silvery color to a clean white--the way most trout and fly fishers see them. Trout also grow fat on Mysis because the shrimp are available most of the year, especially in winter or when the releases from the dam are high. According to aquatic expert Pat Martinez, Mysis prefer water temperatures below 57 degrees Fahrenheit and have an aversion to light. Thus, they stay near the bottom of their home reservoirs during daylight hours. As night falls, however, they migrate upward in the water column. During winter, when many Western reservoirs freeze over, the Mysis is more evenly distributed from top to bottom in a lake's colder water. While trout can grow huge on Mysis shrimp, this food source is not always available, and obese trout have to eat almost constantly to maintain their body weight. Midges hatch almost every day of the year, and many Mysis-fed trout are caught on midge larva imitations. Small Pheasant Tail Nymphs imitate the Baetis nymphs which are often present, and at times, these giant trout will clobber dry flies. Dan Wright is a freelance writer and fly-fishing guide. 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