Cox and Heintz: Electrical phase angle as a new method to measure fish condition 
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We obtained brook trout (rc = 16, mean weight=15.29 g, 
SD=1.21) from the Bowden State Fish Hatchery, Bowden, 
WV, and transferred them to West Virginia University. 
Before transfer, fish were fed standard hatchery trout 
pellets ad libitum approximately three times per day. 
After transfer, fish were randomly selected to be in one 
of two groups (n = 8): fasted or fed. Each fish was housed 
in individual 33L aquaria at 14-16°C. Fish in the fed 
group were offered ad libitum rations of fly larvae (Sar- 
cophaga bullata) (Grubco Inc., Hamilton, OH). Each 
week for nine weeks, all fish were anesthetized with 
a solution of 1 g tricaine methanesulfonate (MS-222, 
Argent Chemical Laboratories, Inc., Redmond, WA) to 
9 L water, and measured for length, weight, and imped- 
ance (i.e., eight replicates for each of two groups every 
week for nine weeks) according to the methods in Cox 
and Hartman (2005). 
Laboratory study 2: fasted and fed rainbow trout 
The effect of malnutrition on phase angle measures was 
measured in rainbow trout in fresh water by repeatedly 
measuring the phase angle in fed and fasted juvenile 
rainbow trout over a period of four weeks starting in 
December 2004. Rainbow trout used in this study were 
raised and housed at the U.S. Department of Agricul- 
ture, Agricultural Research Service, National Center for 
Cool and Cold Water Aquaculture (USAD/ARC NCCWA) 
in Leetown, WV. Two weeks prior to the experiment, 
11 small (mean weight=68.76 g, SD = 6.02) and 12 large 
(mean weight=193.03 g, SD = 15.72) fish were individu- 
ally placed in 2.75-L and 9.0-L aquaria and fed standard 
hatchery pellets ad libitum. Two days before the start 
of the experiment, all fish were fed standard hatchery 
pellets at a rate of 2% body weight per day. At the start 
of the experiment each size class of fish was randomly 
split into two groups: fasted ( n = 11) or fed (n = 12). Fed 
fish were offered hatchery pellets at a rate of 2% body 
weight per day and all holding tanks were kept at 15®C 
for the duration of the experiment (four weeks). Every 
week for four weeks, each fish was anaesthetized with 
MS-222 (lg/9L water) and measured for impedance. 
Laboratory study 3: fasted and fed Chinook salmon 
We tested the effect of malnutrition on phase angle mea- 
sures in Chinook salmon in salt water. Impedance was 
repeatedly measured in fed and fasted juvenile Chinook 
salmon over a period of 13 weeks (mean weight=10.25 g, 
SD=2.23). In November 2007, fish reared at the National 
Marine Fisheries Service (NMFS) research hatchery at 
Little Port Walter, AK, were transferred to the Auke 
Bay Laboratories, Juneau, AK. Fish were acclimated 
for approximately one month during which time salin- 
ity was increased from 0 to 32 and were then randomly 
assigned to fasted (n= 7) or fed (?i = 12) groups. Pairs of 
individually marked fish (fin clipped) were placed into 
8-L aquaria and held at 4°C. Bioelectrical impedance 
was measured in individual fish on weeks 1, 8, 11, and 
13, and different numbers of fasted and fed fish were 
measured each week. The number of fed and fasted fish 
measured in each sampling week were as follows: week 
1 in = 12 and 7); week 8 (n = 4 and 7); week 11 (n- 8 and 
5); and week 13 (n = 5 and 5). 
Differences in phase angle in the laboratory stud- 
ies were analyzed by a repeated measures analysis of 
variance (ANOVA). The analysis was used to test for 1) 
significance differences in phase angle means between 
fed and fasted groups, 2) a time effect on group means, 
and 3) interactions between time and group means. A 
linear mixed-effects (LME) model for repeated measures 
was used to compare phase angles from the start of the 
experiment with those measured after the start. 
Field study 1: wild and hatchery brook trout 
To determine if phase angles differed between hatchery 
and wild fish, phase angles were compared between 
wild fish foraging under natural conditions and cap- 
tive fish fed ad libitum. In July 2002, phase angle was 
measured in 56 brook trout, 34 from headwater streams 
(mean weight=21.21 g, SD = 12.85) and in 11 brook trout 
from Bowden State Fish Hatchery, Bowden, WV (mean 
weight=43.17 g, SD = 4.76). Before they were measured, 
hatchery-reared trout were fed standard trout pellets 
ad libitum three times each day according to standard 
hatchery procedures. Wild fish were captured by elec- 
trofishing from unidentified streams located within the 
Middle Fork watershed in Randolph County, WV. After 
capture, impedance was immediately measured in both 
groups. A two-sample t-test was used to compare cal- 
culated phase angles between hatchery and wild fish. 
Internal fish temperature was not measured, but water 
temperatures measured in both areas were similar 
(mean=13.36°C, SD = 0.94). 
Field study 2: phase angle in migrating chum salmon 
The effect of migration on phase angle was compared 
in migrating adult chum salmon. On 4 August 2004, a 
total of 47 chum salmon (mean=3438.29 g, SD = 511.41) 
were collected by gillnet from a downstream site in the 
Yukon River near Emmonak, AK. During 27-29 Sep- 
tember 2004, 40 chum salmon (mean weight=2927.50 g, 
SD = 470.13) from an upstream site in the Yukon River 
near Delta, AK (approximately 3200 km upstream from 
Emmonak), were collected by gillnet. Impedance mea- 
sures on both the dorsal and ventral (gonadal) areas of 
each fish were measured within one hour of capture. 
Internal temperatures were taken by a digital thermom- 
eter on both groups of fish in the anal vent (downstream 
mean temperature = 16.44°C, SD = 1.22; and upstream 
mean temperature = 3.00°C, SD = 0.48). A two-sample t- 
test was used to compare phase angles of upstream and 
downstream salmon. 
Field study 3: overwintering Pacific herring 
We monitored phase angle in Pacific herring during 
winter to determine if decreases in fish condition due 
