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237 diameter and 15.2 cm in length to reduce turbu- lence as water passed through the working section. Another 2000 straws filled the channel after the working section to counteract flow deflection in- duced by the exit pipe positioned on the side wall. A two-dimensional force beam was mounted on a bridge over the top of each flow tank. We fitted the fish casts to a round 0.635 cm diameter stain- less steel rod (sting) that was 66 cm long. The sting was planed at 90° angles approximately 5.1 cm before mounting to the bridge and foil strain gauges were attached to each of the planed sur- faces. We used standard force-measuring tech- niques in the construction of the force beam (Vogel 1994). Resistors in the foil strain gauges converted bending forces of the metal rod into voltage changes which were picked up in the amplifier circuit by strain gauges. We used a two channel half-bridge amplifier to gather both drag and lift voltage values together during the same trials. We sampled these values 50 times s-1 for a 30 s interval during each trial and recorded data with a Windaq Data Acquisition program. We tested casts of each species, species with humps removed, and the sphere in at least 10 trials per each velocity tested. We used a Dataq cast DI-220 analog-digital converter to transfer sampled volt- age values from the amplifier to a computer. Previous researchers measuring lift and drag components of fishes have attached force balances at the nose, abdomen, caudal, and dorsal regions, with each position having its own inherent hydrodynamic problems (Webb 1975). In pre- liminary studies, we compared lift values when the sting was mounted both dorsally and laterally, and found that attachment of the sting through the dorsum of the fish cast resulted in a small, but significant increased lift as an artifact of the sting. Therefore, we fixed the sting to the lateral surface of the casts, which were positioned on their side (Figure 2) and we calculated residual drag from the sting while determining drag and drag coeffi- cients. We quantified the dynamic fluid-induced forces on the fish casts by calibrating the force beam with a known force (weights). We determined drag ex- erted on the fish body forms at water velocities of 0.3 and 0.9 m s-1. The casts were positioned at a zero degree angle of attack, 0.15 m from the bot- tom and midway between the sides in the 18.3 m flume, so that surface waves and frictional boundary layers with the flume would not affect drag and lift forces (Figure 2). The casts were also placed at a zero degree angle of attack, 0.1 m from the bottom and midway between the sides in the smaller flow tank. Predation Results of flow tests demonstrated that, as an adaptation, large nuchal humps were not advan- tageous to life in fast flowing water and so we sought a more plausible explanation. Because the hump produces the general effect of making the fish much larger in body depth, it might also make a fish less vulnerable to predation. The only native piscivore of concern for larger-size fish is P. lucius, and thus we hypothesized that the increased body size could have developed in response to P. lucius predation. This hypothesis was evaluated by measuring effective mouth gapes of the predator and obtaining body dimension measurements from prey species that possessed nuchal humps and those that did not. In this way we could contrast potential vulnerability to P. lucius predation. We measured body depths in G. cypha and X. texanus as the linear distance from the base of the pectoral girdle to the dorsal nuchal ridge. In addition, we also measured body depths of G. ro- busta and C. latipinnis for comparison. We ob- tained data from preserved specimens in the Repository for Southwestern Species at the U.S.G.S. Biological Resources Division in Fort Collins, Colorado, and at the University of Colo- rado Museum. We also obtained body dimensions from live fish at the Dexter National Fish Hatch- ery at Dexter, New Mexico. We anesthetized live fish using 100 mg 1-1 Finquel Tricaine Methane- sulfonate (MS-222) in order to reduce the amount of stress on the fish and make it easier to obtain measurements. We took body measurements from 719 individ- uals of prey species, including sizes that ranged from small juveniles to large adults. Measurements included: total length (mm), standard length (mm), dorsoventral body depth at nuchal hump region, and maximum dorsoventral depth. We took total length and standard length on a fish measuring board and we measured the body depths with a digital caliper.