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. METHODS . Given difficulties with capturing sufficient numbers of wild larvae to assess entrainment patterns in 2003 pilot studies, we used both beads and hatchery-produced and marked razorback sucker larvae released prior to sampling events to increase capture rates. Beads were semi- buoyant, gelatinous in texture, biodegradable, and three to six mm in diameter (manufactured by Key Essentials, Inc.). Number of beads released was estimated by counting beads in subsamples of a known volume and estimating bead number by scaling that ratio to volume per barrel. Different bead colors were sometimes used at different release locations to understand cross- channel bead mixing rates as beads were captured downstream. Razorback sucker larvae used in releases were produced at Ouray National Fish Hatchery (Ouray Hatchery). Larvae were produced in temporally spaced batches by sequentially spawning groups of adults. We released larvae that were approximately as old as those captured in the wild during the post-spawning period (9 to 15 days old; Muth et al. 1998), although we did release slightly older fish (21 days old) in the first release in 2006. We marked larvae to distinguish hatchery-released larvae from those produced in the wild. Larvae were marked when they were about seven days posthatch or older and just after swim-up (Muth and Meismer 1995). Fish larvae were placed in a reduced volume of water in hatchery tanks or pails and allowed to acclimate for one to two hours (hr). Dissolved oxygen levels were monitored at intervals and maintained at greater than five milligrams/liter (mg/L). Marking was conducted inside and away from any source of ultraviolet light, as light in that wavelength degrades the tetracycline marking compound (Muth and Bestgen 1991). In 2006 we experimented with commercially available tetracycline hydrochrloride (TC) powder (Sigma Chemical T3383), available in feed stores and used for livestock treatments. That compound worked successfully in tests and since it was less . . . . . . . . 19 .