Cox and Heintz: Electrical phase angle as a new method to measure fish condition 
481 
those in week 1 (LME, P<0.001, df=63). In contrast, 
there were no differences in phase angle between 
weeks 2 and 9 and week 1 in the fed fish (LME, 
P> 0.05, df=63) (Fig. 2). The fed group increased 
in size (mean = 15.5 g to 68.5 g) over the same 
time period, whereas the fasted group lost mass 
(mean=15.0 g to 11.9 g) (Cox, 2004). 
In rainbow trout, ANOVA results were similar 
for both small and larger fish and interactions of 
phase angle between feeding group and time were 
significant (ANOVA, P<0.05, df=3) (Fig. 3, A and 
B). In the fasted group for both small and large fish, 
phase angle was significantly lower in weeks 3 and 4 
than in week 1 (LME, P< 0.03, df=40). At the start 
of the experiment one fish from the fed group died; 
however, no changes in phase angle were detected 
between weeks 2-4 and week 1 in the fed group 
(LME, P>0.09, df=43). Small fish in the fed group 
grew in size from a mean of 66.4 g to 98.7 g, and 
large fed fish grew from an average of 197.2 g to 
297.7 g. Likewise, small fish in the fasted group lost 
weight from a mean of 87.8 g to 80.5 g, and larger 
fasted fish decreased in weight from an average of 
188.7 g to 172.0 g. 
Results of the Chinook salmon experiment were 
similar to those of the brook and rainbow trout ex- 
periments, but phase angles in the saltwater fish 
were generally lower than those of the freshwater 
fish. The interaction between feeding group and 
time was significant (ANOVA, P<0.001, df=3) as phase 
angle decreased with time in the fasted group (LME, 
P<0.009, df=20), whereas it increased in the fed group 
(LME, P<0.04, df=20) (Fig. 4). Phase angle changes 
were consistent with changes in wet mass. The fasted 
fish lost an average 0.2% of their wet mass per day. In 
contrast, the fed group gained an average 0.2% of their 
wet mass per day. Phase angles were lower in Chinook 
salmon than in rainbow or brook trout in both fed and 
fasted groups. Phase angles for Chinook salmon and 
rainbow, and brook trout in the fed groups averaged 
15.6°, 16.2°, and 16.5°, respectively, and 13.4°, 15.0°, and 
14.5°, respectively, for the fasted groups. 
Field studies 1-3 
Phase angle reflected changes in the presumed nutri- 
tional status of wild fish in each of the field studies. In 
comparisons between hatchery and wild trout, mean 
phase angle was significantly higher in the hatchery 
trout (two-sample t, P-0.04, t=2.03, df=53). Mean values 
for hatchery and wild brook trout were 19.43° and 18.27°, 
respectively (Fig. 5). Similarly, comparison of adult 
chum salmon sampled in the Yukon River indicated that 
upstream fish had significantly lower phase angles (two- 
sample t, P< 0.001, f=16.5, df=72) from the dorsal mea- 
sures, but not from the ventral measures (two-sample 
t, P= 0.15, t=— 1.4, df=65). Downstream and upstream 
phase angles averaged 23.98° and 17.53°, respectively, 
