BASALT - Mysis shrimp, or "mysis relicta" are one of the reasons we have such big fish in the Fryingpan River.
After the last ice age, these relatives of saltwater shrimp became stranded inland and evolved to become freshwater tolerant. Beginning in the 1950s, these shrimp were stocked in some of Colorado's reservoirs, including Reudi Reservoir just outside of Basalt.
Our fish in the Fryingpan are fed these morsels year-round in the upper miles of the river, as they are flushed from the deeps of the reservoir into the spillway, also known as the "toilet bowl." The amount of protein in these shrimp is very high, resulting in larger than average trout.
These shrimp abhor sunlight and prefer the deeper, darker depths for habitat, though they are known to rise to the surface at night to feed on zooplankton. The dam on Ruedi Reservoir is a "bottom release" structure, which results in thousands of mysis daily being flushed out to hungry trout in the river below.
Healthy mysis shrimp are clear to translucent, and they turn white when dead or dying. There are perfect patterns to imitate these stages of the life cycle, such as Will Sand's epoxy mysis (clear) and Tim Heng's TC mysis (white). The white patterns tend to produce better farther away from the dam, and the clear work best closer to the spillway. Many of us carry a lot of different patterns for these shrimp, including our own secret recipes. It seems they always want one particular pattern on each particular day, so keep a few different styles of mysis flies in your boxes.
One interesting side note about the stocking of these shrimp in Colorado is that they were introduced primarily to feed Kokanee salmon, which were also introduced by man. The only problem with this scenario was that Kokanee have poor eyesight, and therefore couldn't see these shrimp to eat them. Additionally, salmon are more comfortable at different depths than these shrimp prefer. The positive result of this miscalculation is larger than average lake trout, or Mackinaw (lakers see these shrimp just fine) and larger than average fish in the tailwaters below these reservoirs.
Mysis have a neutral buoyancy, and flies are therefore readily fished high to low in the water column. Pay close attention to how and where the trout are feeding when you fish these flies, and adjust your rig accordingly. Your best bet to find the biggest fish feeding on these bugs is when our flows are raised, resulting in more shrimp spilling out of the dam.