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<br />1 <br />f <br /> <br /> <br /> <br />1 <br /> <br />1 <br /> <br /> <br />more natural habitats. Very little information exists concerning growth rates of young <br />razorback suckers in natural environments because survival rates are negligible <br />(Minckley et al. 1991, Marsh 1995, Mueller 1995). <br />Growth rates of razorback suckers that have been spawned and reared under hatchery <br />conditions have been highly variable. Newly-hatched larvae are generally 7-9 mm TL <br />(e.g., Hamman 1985, Papoulias and Minckley 1990, Tyus and Severson 1990). Larvae <br />fed brine shrimp reached an average length of 23.2 mm after 50 days (Papoulias and <br />Minckley 1990). Larvae (i.e., swim-up fry) produced from ripe females in the Green <br />River and reared on natural foods in ponds at Ouray, Utah, grew to an average total <br />length of 127 mm (range: 49-205 mm) during the 1987 growing season (i.e. April to <br />October) and 156 mm (range: 40-271 mm) in 1988 (unpublished data on file with the <br />U.S. Fish and ~Idlife Service, Vernal, Utah). <br />In Lake Mohave, growth of razorback sucker larvae has been studied in isolated <br />backwaters from which other fishes have been removed. In one study, fish grew as <br />much as 35 cm between January and November, 1992 (N=296; Mueller 1995). In other <br />studies, larvae hatched in late March attained average length of 18.9 cm by December <br />(IV=12; Minckley et al 1991). Marsh and Langhorst (1988) evaluated the feeding and <br />fate of wild razorback sucker larvae in Lake Mohave and also found that fish placed in <br />a backwater free of predaceous fishes survived and grew rapidly. <br />23 <br />