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Flow Chamber Experiments Razorback Suckers Razorback suckers display the ability to "draft," maintaining their position fot prolonged periods of time without having to swim. This made the test more of a comparison of this behavioral skill rather than physiological stamina. The chamber has a laminar flow filter constructed of 16-cm drinking straws, which redirects turbulence into parallel flow down the flow chamber. During our initial trials, some fish found what we called the "sweet spot," which was a location near the bottom of the laminar flow filter. Here fish could literally glide through the experiment. On close examination we found that their head was against the chamber's floor, their pectoral fins were arched outward, flat against the sides of the chamber, and the posterior portion of their body angled upward. Apparently there was enough downward force to hold the fish in place. One fish used this technique and endured 4.5 hours and velocities that reached 1.0 mls. To reduce access to the "sweet spot," we built and installed a coarse screen that was positioned about 35 cm downstream of the filter. This reduced the length of the chamber to about 80 cm or about two-thirds of its original length, but prevented the prolonged drafting that we had witnessed before. While this helped, it did not eliminate the problem (behavior) entirely. Fish were still able to maintain themselves for periods of time without actively swimming. Taking advantage of this ability, they were able to hold themselves for a few seconds at velocities of 3.0 BUs. Many would gradually slide hack ward. and upon reaching the screen, they would swim with a burst of energy to reestablish their pOSition at the upper end of the flow chamber. There they would once again start their slow "slide" downstream. These respites undoubtedly helped fish conserve energy. We determined critical flow velocities (Uc,J for 60 razorback suckers: 29 unexercised fish and 31 exercised fish. Summary data (table 1) indicated exercised fish had somewhat higher critical flow velocities and endurance than unexercised fish, but the difference was not significantly different. Table 1. Comparison of distribution of body measurements, endurance (length oftime fish endured increasing flows before exhaustionl, and critical flow velocities (Ucrit) tolerated by unexercised and exercised razorback suckers used in flow chamber experiments. Treatment Statistical Total length Weight Endurance U.,~ U.,~ measurements Mm min emls body len this Exercised Mean :t SE 221 :t 2.5 98.4 :t 3.5 174.3 :t 6.9 53.1 :t 2.5 2.40 :t 0.11 (n = ~ I) Range (200-245) (58-137) (64-236) (11.9-75.5) (0.56-3.43) Variance 194.7 381.1 1465.3 192.3 0.41 Skew. coeff.' 0.41 0.26 -2.67 3.26 2.81 SW p-value' 0.16 0.84 0.01 0.00 0.01 Unexercised Mean :t SE 224 :t 2.6 100.0:t 3.5 166.3:t 7.4 50.4 :t 2.7 2.25 :t 0.12 In = 29) Range ( 198-245) (62-130) (80-241) (16.7-74.4) (0.82-3.43) Variance 193.2 357.9 1594.4 211.9 0.43 Skew. cneff.' -0.44 0.67 1.02 1.33 1.09 SW p-value' 0.20 0.49 0.48 0.43 0.44 'Skewness coefficient = skewness/SE of skewness is considered significant if the absolute value is greater than 2. 'sw p-vaJue: a significant p-value indicates data are not normal based on Shapiro-Wi1k normality test. 11