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<br />CLARKSON AND CHILDS-TEMPERATURE EFFECTS ON FISHES
<br />
<br />preimpoundment poisoning operation in 1962
<br />(Vanicek and Kramer, 1969; Holden, 1991). In
<br />addition, no reproduction by any native species
<br />was observed in the reach below the dam to
<br />Yampa River during years with high spring-sum-
<br />mer flows and concomitant low water tempera-
<br />tures (Vanicek et aI., 1970). Following warming
<br />of spring-summer tailwater temperatures to
<br />highs near 13 C after retrofit of Flaming Gorge
<br />Dam with temperature controls in 1978, repro-
<br />duction by many native fishes was restored in
<br />the lower reach (P. B. Holden and L. W. Crist,
<br />unpubI.).
<br />In the Colorado River and tributaries be-
<br />tween Glen Canyon Dam and Lake Mead, Ari-
<br />zona (the Grand Canyon system), P. lucius, G.
<br />robusta, and G. elegans were extirpated following
<br />lowering of spring-summer tailwater tempera-
<br />tures to near 10 C after completion of Glen
<br />Canyon Dam in 1963 (Minckley, 1991). Gila 0'-
<br />Pha distribution in the Colorado River contract-
<br />ed (R. Valdez and R. J. Ryel, unpubI.), and X.
<br />texanus is extremely rare and functionally extir-
<br />pated, with no evidence of reproduction. Main-
<br />stem reproduction by Catostomus latiPinnis
<br />(Flannelmouth Sucker) also has been reduced
<br />or eliminated (Weiss, 1993). Most successful re-
<br />production by remaining native fishes in the
<br />Grand Canyon system now occurs only in trib-
<br />utaries (Kaeding and Zimmerman, 1983;
<br />Schmidt et al., 1998). Glen Canyon Dam is now
<br />being considered for modification to allow re-
<br />lease of warmer epilimnetic water for benefit of
<br />native fishes.
<br />We investigated effects of depressed water
<br />temperature on Colorado River Basin big-river
<br />fishes by examining certain growth, physiologi-
<br />cal, and developmental responses of early life
<br />stage X. texanus, C. latipinnis, G. 0'Pha, and P.
<br />lucius in the laboratory. Quantification of tem-
<br />perature impacts will identify management im-
<br />plications of temperature depression and en-
<br />hance development of management options to
<br />assist conservation and recovery of this imper-
<br />iled ichthyofauna.
<br />
<br />MATERIALS AND METHODS
<br />
<br />J
<br />
<br />Temperature experiments were conducted at
<br />Bubbling Ponds State Hatchery near Cornville,
<br />Arizona. Water was from a pathogen-free arte-
<br />sian well at 18.6 C, 7.6 pH, 366 fLS/cm specific
<br />conductance, and 4.3-7.3 mg/L dissolved oxy-
<br />gen.
<br />
<br />Culture.-Gametes of G. 0'Pha were collected
<br />26-27 April 1993, from pituitary-injected, man-
<br />ually stripped fish caught in the lower Little Col-
<br />
<br />403
<br />
<br />orado River, Grand Canyon, Arizona. Fertilized
<br />eggs were incubated 1-3 days on screens float-
<br />ing in 19-1iter buckets filled with aerated, desilt-
<br />ed river water. Water temperatures in the buck-
<br />ets, which were partially submerged in the river,
<br />ranged from 16 C to 21 C. Following transport
<br />to Bubbling Ponds Hatchery, embryos were ac-
<br />climated to ambient 18.6 C water over 90 min
<br />and treated daily with 1667 ppm formalin for
<br />15 min as prophylaxis against fungus during fur-
<br />ther incubation in Heath trays. Larvae were
<br />transferred to shallow troughs of through-flow-
<br />ing 18.6 C water until swim-up and transferred
<br />to aquaria at 20 ::': 0.5 C. Larvae were fed Artem-
<br />ia salinus nauplii, zooplankton from hatchery
<br />ponds, and Bio-Kyowa commercial feed ad libi-
<br />tum three times daily. Beginning 2-4 weeks fol-
<br />lowing swim-up, larvae and juveniles were fed
<br />commercial trout feed of progressively larger
<br />sizes as needed.
<br />Hatchery broodstock P. lucius was spawned 20
<br />May 1993, and embryos were incubated in
<br />hatching jars in 18.6 C water. Newly hatched lar-
<br />vae were transferred to flow-through troughs at
<br />18.6 C for a few days prior to 90 min acclima-
<br />tion to 20 ::': 0.5 C aquaria. Feeding was as de-
<br />scribed for G. 0'Pha.
<br />Embryos from X. texanus broodstock were cul-
<br />tured at 18-21 C in Heath trays at Dexter Na-
<br />tional Fish Hatchery in Dexter, New Mexico,
<br />and hatched 8-9 March 1994. Swim-up larvae
<br />were air-transported to Bubbling Ponds Hatch-
<br />ery and acclimated to 20 ::': 0.5 C aquarium wa-
<br />ter over 90 min. Feeding (five times daily) and
<br />other treatments were identical to those for G.
<br />0'pha, except that zooplankton was not provid-
<br />ed.
<br />Catostomus latipinnis gametes were taken from
<br />naturally ripe, manually stripped fish caught in
<br />Colorado River near Lee's Ferry, Arizona, on 14
<br />May 1995. River temperature at time of collec-
<br />tion was 12 C. Embryos were placed in a sealed
<br />bag filled with river water and oxygen, trans-
<br />ported to Bubbling Ponds Hatchery, and accli-
<br />mated to 18.6 C water over 90 min.
<br />Embryos were incubated in hatching jars at
<br />18.6 C and treated once with 0.025% betadine
<br />in a 10-min bath to control aquatic fungi. Young
<br />hatched 21-22 May, and larvae were acclimated
<br />to aquaria at 20 ::': 0.5 C as described for other
<br />species. Larvae were fed ad libitum five times
<br />daily as described for X. texanus.
<br />
<br />Growth experiments.-Experimental temperatures
<br />of 10, 14, and 20 C were selected to simulate
<br />spring-summer reproductive and rearing con-
<br />ditions extant in the mains tern and major Col-
<br />orado River tributaries. Although variable, tail-
<br />
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