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Volume 1 (Issue #3), 1993 X-RADIOGRAPHY IN FEEDING AND GROWTH STUDIES <br />a curvilinear one, and logarithmic transformation is a suitable method for linearizing <br />the data (Jobling et al., 1989; Christiansen and Jobling, 1990). Data were log- <br />transformed, following the addition of 1.0 in order to remove negative values, and <br />the best fit to a straight line of the form: <br />loge(SGR + 1) = a + b loge(FI + 1) <br />obtained by regression analysis using the least squares method. Results of the feed- <br />growth relationships for the groups of fish exposed to water currents equivalent to <br />swimming speeds of 0 and 2.0 body lengths per second are shown in Figure 4. <br />Regression lines were compared using covariance analysis. There were no differ- <br />ences between slopes, but intercept values did differ significantly. Thus, for a given <br />level of feed intake, fish forced to swim at 2.0 body lengths per second grew faster <br />and had higher feed efficiency ratios (weight gain per unit weight of feed consumed) <br />than fish not subjected to flowing water conditions (Figure 4). <br />The improved growth and feed efficiency ratios displayed by the fish subjected <br />to prolonged exercise are probably not caused by a single factor, but rather are the <br />result of several behavioral and physiological changes shown by the exercised fish <br />(East and Magnan, 1987; Houlihan and Laurent, 1987; Christiansen et al., 1989, 1991, <br />1992; Davison, 1989; Christiansen and Jobling, 1990). The growth improvement <br />observed in the groups of charr exposed io water currents appeared to be linked <br />to differences in feed distribution and acquisition among fish held in the different <br />.~ - <br />v <br />0 <br />... <br />d <br />0 1 <br />r <br />3 <br />0 <br />L <br />V 0 <br />V <br />a <br />H <br />C <br />J _1 <br />~ 0.0 BUsec <br />• 2.0 BUsec • • <br />• • <br />0 0 ~ <br />0 ~ oo °o <br />• O <br />0 <br />Q <br />~ ~ 2 <br />Ln feed intake (mg/g fish/day) <br />3 <br />FIGURE 4. Feed-growth relationships of individually tagged, immature Arctic chary subjected to <br />swimming regimes of 0 and 2.0 body lengths per second. The relationships are described by the <br />equations: loge(SGR + 1) _ -0.7420 + 0.5933 loge(FI + 1) (n = 39; r = 0.8&8) for 0 body lengths s-', and <br />loge(SGR + 1) _ -0.3355 + 0.5915 IogB(FI + 1) (n = 45; r = 0.869) for 2.0 body lengths s-'. <br />233 <br />