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9 DISCUSSION The phenomenon of fish predators attempting to feed on spined prey is well studied but primarily from the prespective of the prey (Hoogland et al., 1957; Beyerle and Williams, 1968; Mauck and Coble, 1971; Moodie et al., 1973; Reist, 1980). Ivlev (1961) defined prey vulnerability to predation as having two components, prey availability and predator preference. Prey availability is influenced by several factors such as schooling behavior, cryptic appearance, distribution, and armament. Channel catfish certainly (rave formidable armament and when this was reduced by clipping spines they were consumed more frequently than were catfish with spines intact. However, despined catfish were still consumed far less frequently than were trout. There could be several reasons for trout preference. First, the stumps re- maining after catfish spines were clipped might still feel harsh to the squaw- fish's mouth. However, in preliminary trial H (Appendix). 3 squawfish consumed 20 CCSPL in 5 days, indicating that the stumps provide no real hinderance to consumption. Yet in later trials, the average number of CCSPL consumed per trial was only 2.4. Hoogland et al. (1957) found that northern pike (Esox lucius) could learn-to eat three-spined sticklebacks (Gasterosteu.s aculectus) with little difficulty and in a short period of time. Moodie et al. (1983) showed that northern squawfish (P. oregonense) also has little difficulty with stickleback spines. Moodie et al. (1973) concluded that behavior of the sticklebacks helped protect them from predation. Behavior differences could explain the low channel catfish utilization. Catfish in the size range used tried to form dense schools that shifted continuously across the bottom of the aquarium. The trout, in contrast, form very loose schools at the surface that are easily dispersed when a predator approaches. These differences in