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7/14/2009 5:01:47 PM
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UCREFRP
UCREFRP Catalog Number
8136
Author
Bestgen, K. R.
Title
Growth, survival, and starvation resistance of Colorado squawfish larvae.
USFW Year
1995.
USFW - Doc Type
\
Copyright Material
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<br />Starvation resistance <br /> <br />Survival of Colorado squawfish was about 95% for <br />treatments where larvae were denied food for 0 <br />(control), 5, or 10 d (Fig. 6). Survival of larvae de- <br />nied food for 15 d after normal first feeding de- <br />clined from 93 % to 87 % after first feeding. Survival <br />of larvae denied food for 17,5 d declined from 84 % <br />before to 63% after feeding began, but was 57% at <br />the end of the experiment. Only 6% of Colorado <br />squawfish denied food for 20 d survived to the end <br />of the delay period, and only 1 % survived after food <br />was offered. Point of no return is defined here as the <br />time over which a batch of larvae are denied food, <br />are then offered food, and have cumulative mortal- <br />ity ~ 50%. Point of no return for Colorado squaw- <br />fish larvae was between 17.5 and 20 d. <br />Lengths of fish in all treatments increased during <br />the first 5 d, then growth slowed if fish were not fed <br />(Fig. 7). Fish denied food for 0 or 5 d grew at very <br />similar rates. Fish in treatments where feeding was <br />delayed 10, 15, or17,5 d grew immediately following <br />feeding. Growth rate trajectories observed for fish <br />in these treatments were similar to those observed <br />in treatments where fish were denied food for 0 and <br />5 d. Fish were, of course, smaller when denied food <br />for 10 or more days. Most fish in the 20 d treatment <br />died prior to feeding so no observations of post- <br />feeding growth were possible. <br /> <br />Discussion <br /> <br />, <br /> <br />Growth response <br /> <br />Growth of Colorado squawfish larvae based on <br />model results was optimal at 310 C and food abun- <br />dance of 345 nauplii fish-I day-1, conditions which <br />were similar to the highest ones tested (300 C and <br />320 nauplii fish-1 day-l). Because the predicted tem- <br />perature maximum is warmer than the highest one <br />studied, it is not possible to determine if the true <br />optimum for growth of Colorado squawfish larvae <br />is 310 C. Environmental observations suggest that <br />Colorado squawfish larvae occupy habitat where <br />water temperatures were as high as 28-320 C (Dill <br />1944, Tyus & Haines 1991, personal observation). <br /> <br />205 <br /> <br />14 <br /> <br />Control <br />5 days <br /> <br />13 <br /> <br /> <br />15 days <br />10 days <br />17.5 days <br /> <br />12 <br /> <br />f' <br />I <br />1,0 <br />.f'" <br />......, . <br />.' I ! <br />0/ / /' <br />t ,; <br />I i <br />I i <br />I / <br />I ! <br />I i <br />I / <br />.0 f ,/ <br />9 ~,- I i <br /> <br /><;,; ).:~:.~;3:7:~...~:;.-~-l-/-It./ OIl <br />8 </'-" <br />/ <br /> <br />E 11 <br />E <br />..... <br /> <br />.c <br />- <br />Cl <br />; 10 <br />...J <br /> <br />sJ <br /> <br />20 days <br /> <br />7 <br />o <br /> <br />5 <br /> <br />10 15 20 25 30 <br />Time (days) <br /> <br />Fig, 7. Growth of Colorado squawfish larvae (n '" 5-10 individu- <br />als) denied food for 0 (control), 5, 10, 15, 17,5, and 20 d after fish <br />were first able to feed, <br /> <br />Thus, the estimated optimal growth temperature of <br />310 C may be realistic. <br />Significant LOF was detected for the growth re- <br />sponse model, in spite of R2 = 0.98. The relatively <br />large number of replicates per treatment after pool- <br />ing regimes resulted in 100 degrees of freedom for <br />the pure experimental error term (divisor in F-ratio <br />LOF test) and 14 degrees of freedom to estimate <br />LOF (numerator in F-ratio). The large sample size <br />and small pure experimental error mean square <br />probably resulted in relatively high power to detect <br />a small amount of LOP. Residual plot analysis is <br />useful to detect model LOF if, as in this study, the <br />number of observations is large with respect to the <br />number of parameters being estimated (Box & <br />Draper 1987). Thus, the growth response model was <br />considered an adequate representation of the ex- <br />perimental data. <br />Fluctuating temperature regime had no effect on <br />growth or survival compared to constant temper' <br />ature conditions in this study. Some studies of ef- <br />fects of fluctuating temperature regimes on growth <br />of fishes showed positive effects whereas other <br />
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