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,.,. Table 4. Potential predators used in chronological order in razorback larvae trials, 2003. Razorback Predator Predator larvae Dates and Predator size range biomass size range duration of species (mm) glm3 (mm) trials Oriein of predators Red shiner 46- 65 TBA 9 -12 21-22 Mar; Virgin River 26 hours Bonytai1 57-75 TBA 9 - 12 23-24 Mar; Willow Beach Hatchery 24 hour Lepomis sp. 37-57 TBA 12 - 16 26-27 Mar; Colorado River below Davis 24 hours Dam Rainbow trout 40-51 TBA 12 - 15 27-28 Mar; Willow Beach Hatchery YC-l 14 hours Bullfrog 72-87 TBA 10-15 11-12 Apr; CHLP tadpole 24 hours Yellow 91-138 TBA 10 - 15 12-13 Apr; Irrigation ditches surrounding bullhead 18 hours Achii Hanyo Hatchery Rainbow trout 123-182 TBA 18 - 28 28-29 May; Willow Beach Hatchery Adult 14 hours Bluegill 75-115 TBA 31 - 39 24-27 Jun; Park Moabi, Colorado River 63 hours , Channel 88-126 TBA 30 - 50 10-14 Ju1; Hopper-Stephens hatchery, AK catfish 88 hours Largemouth 62-79 TBA 30 - 45 1-2 & 14-16 Ju1; Anderson Fish Farms, AK bass 24 and 39 hours Tank experiments suggest that tadpoles (n=75) had consumed all the razorback sucker eggs (n=300) within 90 hour. Predation was 100%. There has been a great deal of suspicion but little evidence that tadpoles are competitors or possibly predators on fish eggs and larvae (Boyd 1975, Kaneet al. 1992). A glimpse at the literature provides ample evidence that tadpoles feed on frog and salamander eggs (Morin 1983, Kupferbert 1997, Petranka et al. 1998). It has also been reported that tadpoles excrete a growth inhibitor that interferes with fish spawning (Boyd 1975) and that toxicity from eating frog eggs could cause reproductive failure in other anuran species (petranka and Kennedy 1999). We could find only two references of tadpoles feeding on fish larvae (Savino and Miller 1991, Nguenga et al. 2000). Crayfish-Razorback Sucker Frv. We witnessed similar losses with crayfish. Within 72 hour, 2 crayfish'had killed 96.7% of the razorback sucker young (16.2 nun) in the 'No Cover' experiment (Table 5). Unfortunately, the tests were inconclusive concerning the role of cover. Predation rates in the 'Deep Cover' tests were lower than the control (70%). The shallow tank tests were delayed and we were unable to use razorback sucker fry of the same size. The young razorbacks were substantially larger (20 rom versus 16 18