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<br />254
<br />
<br />The Southwestern Naturalist
<br />
<br />vol. 30,,,,!
<br />
<br />TABLE I.-Change in weight (grams) 0/ yearling Colorado squaw/ish over a 12-week pm'4
<br />adjusted treatment means.
<br />
<br /> MI',IIl
<br />li.'mpnaIUTl' Ralion Initial Ch<lnKt'in
<br />(" C) (% s<il'ia\lon) wt'i~'H weiRhl
<br />15 50 0.46 0.27
<br /> 100 0.46 0.20
<br />20 50 0.45 0.96
<br /> 100 0.48 0.69
<br />25 50 0.45 1.91
<br /> 100 0.43 1.50
<br />30 50 0.44 0.91
<br /> 100 0.43 0.94
<br />
<br />C in a sin~1e 833-liter tank with a 14-hour light x IO-hour dark photoperiod. About 700 [i,h_
<br />then transferred and distributed randomly among eight experimental tanks.
<br />Each experimental tank (100 x 50 x 50 cm; water depth, 15 cm) was divided into ,.
<br />compartments with screens to provide three replicates within each lank. Tanks were surrour*i
<br />by a curtain and provided with low-level lighting. photoperiod [ollowed ambient condition...
<br />averaged 12-hour light x 12-hour darkness. Continuous water [low o[ I to 2 liters per mil""
<br />passed through the tanks. Dissolved oxygen was 90-100% saturation and ammonia below 0.2 I~"
<br />Temperatures were recorded daily and were maintained within 10 C of tesllemperalures.
<br />Fish were brought to test temperatures (15, 20, 25, or 300 C) at rates of ]_20 C per 11;11 .(.
<br />and Coutant, 1981). All test temperatures were reached on the same day. An ink!1I'''.
<br />lcthyopthirius multi/ilis was treated with formalin and periodic increases of tempe"Il11~ 0
<br />points above 300 C in all tanks before the growth experiment began. Alter treatmem, ,Ii< ...
<br />were a(c1im(lH~d to experimental temperatures {or at least 1 week before initial mrasun.'ffit'lIh ...
<br />taken and ration levels determined (Cox and Coutant, 1981).
<br />Groups of 20 [ish per replicate were then selened (or uniform. intermediate size. Ml'an ."".-
<br />was 0.45 g (SD = 0.11 g) and mean total length 45 0101 (SD = 3 0101). Several fish anil.....
<br />to 150 C died [rom the lclhYOPlhirius infection, and replicate size was reduced to 10 for ,II loll
<br />acc:limated to 150 C to enable us to use only healthy fish. Fish were not led [or I da\ t.W
<br />measurements were made. Wet weights (to the nearest 0.01 g) and len~ths (to tl... nr....
<br />millimeter) were determined after fish were lightly anesthetilCd with tricaine methane ,,111,....
<br />(MS-222) and blotted on damp toweling (Brett and Shclbourn, 1975; Biette and C"<,n. r_
<br />Measurements were taken first in March 1982 and al three 4-week intervals thereaher. t", ..
<br />in June.
<br />Two ration levels were used, satiation and 50% satiation. The satiation feeding Inf'( ..
<br />determined in the following manner: Starting with a preweighed amount of food. ithmll'"
<br />amounts were given 10 Ihe fish every few minutes for 30 minutes, or until the [ish well' \,1,.....-
<br />Fish were considered satiated when they no longer accepted food, in the presence of ('xu.'\ -
<br />a period o[ active [eedin~ (Brett, 1971). No attempt was made to account [or food ollrl.c"
<br />not eaten. This process was repeat~d at each 4-week inlerval to determine if ration 1['\('1\ ~
<br />to be adjusted. Automatic [eeders dispensed feed at 0800, 1200, and 1600 hours. ''''nl. ..
<br />siphoned daily, at least I hour after a feeding.
<br />Effects of temperature on growth rates were tested by analysis o[ covariance, with initioll--
<br />as the covariate (McCormick and Kleiner, 1976).
<br />
<br />l
<br />
<br />..'..,..........
<br />,
<br />;,j
<br />
<br />RESULTS AND DISCUSSION.-As the experiment progressed, it tlt\_
<br />evident that both rations were providing more (eed than was being r",,"
<br />but levels were not altered during the experiment. The 50% satiation tAl"
<br />resulted in greater total increases in mean weight than did the 1000;, u'...,
<br />(F = 6.19; P = 0.05) (or (ish held at 14, 20, and 250 C (Table I). The rr.Afl!
<br />(or this phenomenon is not known; no outward signs o( SliT" ""
<br />observed during the experiment.
<br />Inasmuch as both rations allowed (ish to feed ad libitum, data onlhr
<br />
<br />'-.
<br />
<br />"., 19H5
<br />
<br />Black and Bulkley-Growth Rate of Squawiish
<br />
<br />2,r)~)
<br />
<br />"llllI! groups were combined to compare temperature di((erences, POOI~lg
<br />... the two ration groups increased the variance so that di((erences detected
<br />b, statistical analysis were more reliable. The e((ect o( temperalurp on
<br /><<",wlh rate was statistically significant on the basis on analysis o(
<br />,,,,.uiance (F = 63.17; P = 0.01). Fish held at 150 C consistently grew
<br />,i"WI'st; those held at 250 C grew the most rapidly. Growth rates wel('
<br />."'illar (or fish held at 200 C and 300 C. Average daily gain was 3.5 mg
<br />,~ 1',0 C, 10.7 mg at 200 C, and 19.8 mg at 250 C (Table 2). Evidently, :{OG
<br />( tl above optimum temperature (or maximum growth when (ood is not
<br />, ""Ied because daily gain dropped to 10.1 mg at this temperature, only half
<br />'" o( fish held 50 C cooler at 250 C. Increases in body length followed
<br />. '"llilar pattern to that o( body weight. Mean length increase per day (or
<br />'r "!I-day period was 0.064 mm, 0.188 mm, 0.256 mm, and 0.169 mm (or
<br />. ,I, held at 150 C, 200 C, 250 C, and 300 C, respectively (Table 2). Average
<br />. If;lse in length o( fish held at 150 C was only 5.4 mm in 84 days vs. 2.'d
<br />'Il lor (ish held at 250 C.
<br />(.rowth data were also examined (or possible e((ect o( the outbreak o(
<br />,!""pthirius at the beginning of the experiment. No (urther evidence o(
<br />. ,'"e occurred during the experiment, but treatment consisting o( raising
<br />" water temperature to above 300 C could have influenced tempnature
<br />. ,11Illalion o( (ish held at the lower temperatures. The brevity o( the
<br />,!'nature increase at the beginning o( the study and the length o( time
<br />"Inl (or thermal acclimation suggest that any e((eets (rom the disease
<br />. >fllll.1It should not have endured beyond the first 28-day segment o( the
<br />"h Growth rate of fish held at 150 C, the group most likely in need of
<br />. 1'f1Mtioll, was compared among each of the three 28-day segments of the
<br />."flll~ study (Table 2). Daily weight gains (or the three time segments wne
<br />j' \'1. and 2.6 mg/day. Mean body weight increased 27% in the first 2H-
<br />" I"" iod, 16% in the second, and II % in the third period. Di((erences were
<br />"l\lltally significant at the 0.01' level o( probability (F = 16_0). Hence,
<br />~ III o( the 150 C fish was evidently not adversely a((ected the first month
<br />, 'I,.. study by any thermal acclimation that might have occurred, and
<br />1"-r;lIl1re e((ects on growth o( the Colorado squaw fish appear to be
<br />.' "IAI.
<br />
<br />I I", u'lIlperature at which maximum growth rate was abserved agreed
<br />" tht, estimated final thermal preferendum (or yearling Colorado
<br />....,I\.h ,of 250 C. Further growth tests at additional temperatures close
<br />" (, (I.e., less than :!: 50 C) would be needed to determine the exact
<br />" 'Illllll growth temperature (or the species when (ood is in excess. Our
<br />.' ','11. lindings support conclusions o( Jobling (1981) that the (inal
<br />'," ,,,~I preferendum provides a good indication o( optimum gnm'f h
<br />;'WtlHt'. Bulkley et al. (1981) (ound that 20 to 260 C was also the
<br />"'"'" temperature range for swimming stamina o( Colorado squawfish.
<br />'.1 1f-'lIlts suggest that reduced water temperature below dams in the
<br />......1" River drainage could well have lowered growth rate o( Colorado
<br />...ll\h from historic levels. For example, after construction o( Flaming
<br />'j(- 11,1111 on the Green River in 1963, mean summer (]une-Septembe;)
<br />", ... ",.., trllll)('rature in the river below the dam dropped (rom about 180 C
<br />~... (ollStruction to 6.80 C after construction (Vanicek and Kramer, 1969).
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