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<br />.!S I ( J.C K1'f""1:)U \ t<. le,(J
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<br />vol. :ill, 1\11, ~
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<br />~ SOUTHWESTER1>i NATURALIST 30(2):253-257
<br />
<br />MAY 31,1985
<br />
<br />Biolog~. <tilt! llll
<br />
<br />--
<br />
<br />I)('ydop:, l'f'T'J(/fl'
<br />
<br />GROWTH RATE OF YEARLING
<br />COLORADO SQUAWFISH AT
<br />DIFFERENT WATER TEMPERATURES
<br />
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<br />t: all 1.00pLll.i
<br />
<br />T AMARA BLACK AND Ross V. BULKLEY
<br />
<br />11 P~'lamid LI~'
<br />and ;\.\'~K. hll
<br />
<br />ABSTRACT.-Growth rate of y,'arlin!( Colorado squawfish. Ptychocheilus lucius, over a 12-week
<br />prriod, was determined for fish held at I.". 20, 25. and .100 C wi,h excess food. The effect of
<br />.....perature on !(rowth rate was hi!(hly si!(nificanl; fastest !(rowth occurred a~. Fish !(ained
<br />.......t 0.3 !(ram at /50 C, 0.9 !(ram at 20 and 300 C, and 1.7 !(rams at 250 C durin!( the 12-week
<br />prriod. Results sug!(est that 250 C. the final thermal preferendum. is the temperature at which
<br />Colorado squawfish !(row fastest with abundant feed. Future water shona!(e and development
<br />pojt'clS should be desi!(ned to provide summer Water temperatures as near this level as feasible.
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<br />One of the major habitat changes imposed on the upper Colorado River
<br />clrainage by dam construction since the 1930's was an altered annual water
<br />'lnnperature pattern which results in much lower summer water
<br />Itfllperatures in significant portions of the drainage. The change in annual
<br />aver temperature was cited as the possible cause of an apparent reduction
<br />in growth rate of the endangered Colorado squawfish, PtychocheiLus Lucius
<br />tvanicek et aI., 1970). Colorado squawfish once attained lengths of up to
<br />! m and weights of 30 to 40 kg. In recent years the largest known specimens
<br />~ only 1 m long and weighed about 7 kg (Behnke and Benson, 1980).
<br />'~nke and Benson considered other possible causes of reduced growth rate
<br />llullemperature reduction is most likely involved.
<br />The objectives of the present study were to determine the optimum
<br />JfOwlh temperature for yearling Colorado squawfish and the relation
<br />kfween optimum growth temperature and final thermal preferendum for
<br />- species. Bulkley et al. (1981) determined thaI the final thermal
<br />_~ndum for both adult and yearling Colorado squawfish is about 250
<br />crPreferred temperature is hypothesized as being the thermal optimum for
<br />illeasl some biological processes, including growth (Beitinger and
<br />( libgnuson, 1979; Coutant, 1980; Magnuson, et al.. 1979). The optimum
<br />reb, C\. InDperature for growth-the temperature at which growth rates are fastest-
<br />Ie. and -.,,,, '\ .. defined by ]obling (1981) as "the temperature at which growth rate is
<br />
<br />of lar!(fl (: ,,; 'I \ Wchnl when fish are reared under conditions of maximum, or excess
<br />-12~S. f ",I\.., lading." Lemke (1977) found preferred and optimum growth temperatures
<br />'A. ,).- \.;,.'k~ close for juvenile bluegills. Lepomis macrochirus. jobIing (1981)
<br />814. in h'jffj \. , .)~. a close correlation betwee~ the fin~1 preferendum and the opti~um
<br />/" · -.perature for growth of 19 hsh speCies. He concluded that the hnal
<br />. Jlldrrrndum provides a good indication of the optimum temperature for
<br />IIOW1h.
<br />ii.~t'.;.
<br />
<br />.....- Yearling Colorado squawfish used in this study were hatched and reared at the
<br />--.... (Ariwna) National Fish Hatchery. They were held in outdoor ponds and fed natural
<br />~ until transfer in January 1982 to the Utah Water Research Laboratory. There they
<br />... .-IuaJly convened to dry troU[ food while being held for J month in water at 14 :t 10
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