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TA approximates total activity by weighting the number of fish in each chamber (nJ by the distance from the central (and initial) chamber (#4). Thus, if a fish were in chamber 1 or 7, the weighting factor would be scored as 3. Similarly, if the fish were in chamber 4 (the central chamber), the weighting factor would be zero. TA does not consider the direction of movement (upstream or downstream), only the distance from the starting point. Thus, the value recorded for each trial is the average displacement of the fish in that trial, and ranges from 0 to 3. The variance of TA is computed from the replicates of the age/ light/ flow combination (usually 5). n; •(4 -r) DA= ~ n; t DA is an approximation of directed activity (i.e., movement) and is calculated as previously described for TA, except direction of movement is considered. DA assigns positive values for movement with flow, and movement to chamber 6, which is downstream, receives a weight of +2. Negative values accrue for distance upstream of the central chamber (#4), and movement to chamber 2, would receive a weight of -2. DA could be zero if all movement were random or if there were no movement. The ratio of DA/TA indicates the extent to which movement is oriented upstream or downstream. Rather than present the results of trials in statistical tables, TA and DA computations aze presented by bar graphs that show the influence of two factors while a third factor is held constant (e.g., flow and age at night). The use of 95% confidence limits on each baz facilitates pair-wise comparisons for significant differences, yet preserves the ability to see broad patterns across factors. Comparisons were organized according to the flow regime (control, slow, and moderate), within which the effects of time of day (night or day) on fish of different ages could be examined. Although there was no flow of water through the experimental tank in the control trials, fish movements were labeled "upstream" or "downstream" for consistency and for comparison with other treatments. RESULTS All age groups tested were active during control, slow, and moderate flow conditions, however there were differences in both TA and DA among groups and test conditions. As expected, large fish moved faster than small ones, but some individuals of even the smallest age group could swim well enough to reach the limits of the tank with all flow conditions. Control With control conditions (i.e., no water flow) at night, the youngest larvae moved very little, razely straying from the central chamber (Figure 2), but oldest fish tended to move more. Activity (TA) of smaller larvae 529