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tended to move upstream. There was no discernable pattern of movement (DA) in the presence of a slow flow during the day. Moderate flow With increased water flow, TA of smaller larvae (CP1, CP2, RZ1) was stimulated at night (Figure 2). Furthermore, TA was similar among the life stages; three-week old larvae showed as much activity as the 36-week old juveniles. During the day, TA had no consistent pattern. However, all fish stages showed downstream movement at night in the presence of moderate flows. In daylight, moderate flow also produced a tendency for net downstream movement of larvae. Juvenile Colorado pikeminnow The 36-week old juvenile pikeminnow (CP4) were very active in day and night conditions and TA reached a relatively steady value in less than 15 minutes, even in the absence of flow. The introduction of a small flow caused the pattern to stabilize more quickly at night, and the direction of movement was strongly affected by flow. In the control trials, there was no net movement upstream or downstream during the night in the absence of flow, and there was only a slight tendency for upstream movement at day. With a slow flow, there was a general trend for upstream movement at night and downstream movement at day. When the flow was increased to moderate, daytime movements tended to be downstream, but visual observations indicated that the movements appeared to be searching (i.e., alternating down- and upstream movement) rather than directed. However, night movements were in the downstream direction (Figure 3). >_ 1 :. U a o d .~ U m -1 -2 -4 -3 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 Time Elapsed, min ®Night ~ Day Figure 3. Average directed activity of 36-week Colorado pikeminnow with moderate flows at 3 min intervals after trial initiation in an experimental tank. The 95% CL shown for each category. 531