Cox and Heintz: Electrical phase angle as a new method to measure fish condition 
485 
stores. However, changes in mass-specific energy 
content can only be detected in tissues when there 
has been a sufficient change in the amount of lipid 
in relation to protein. In contrast, phase angle ap- 
parently changes much faster, reflecting local al- 
terations in membrane potential and water balance. 
Measuring changing phase angles in dead fish 
provides a useful model for illustrating BIA perfor- 
mance in live fish. Phase angle changes with time 
after death owing to rigor mortis, cellular break- 
down, and water movement from intra- to extracel- 
lular spaces. Although timeframes for the onset and 
resolution of rigor mortis depends on species, condi- 
tion of fish at time of death, environmental stress, 
and temperature (Martinsen et ah, 2000; Damez 
et ah, 2007), rigor mortis usually occurs within 
the first 18 hours of death, when muscles remain 
contracted until resolution. This period is reflected 
in our data as an increase in phase angle with 
time. Human studies involving muscle contractions 
and impedance indicate that muscle contractions 
result in an increase in R and Xc (Kashuri et ah, 
2007). Our study was consistent with Kashuri et 
al. (2007) in that Xc increased during rigor mortis 
(contraction). Their study indicated that increases 
in Xc were due to cell membrane and intracellular 
changes (possibly metabolites) and not to volumetric 
or morphological changes. In our study, decreases 
in impedance upon resolution (relaxation) were most 
likely due to the physical breakdown of cell mem- 
branes and subsequent autolysis and nucleotide 
catabolism. The breakdown of cell membranes and 
muscle hydrolysis causes the release of electrolytes 
and water into extracellular space, therefore de- 
creasing the phase angle (area of decreasing slope 
in Fig. 8). In a study of postmortem changes in 
dielectric properties of haddock ( Melanogrammus 
aeglefinus) muscle, Martinsen et al. (2000) found 
that the onset and resolution of rigor mortis af- 
fected R levels at multiple frequencies and they 
associated the increase with a response to edema. 
This makes the use of phase angle applicable to 
measuring changes during the postmortem period 
in fish after the resolution of rigor mortis, therefore 
allowing phase angle to determine time of death in 
fish where ambient temperature is known. 
It is important to know that phase angles were 
only slightly affected by temperature and not af- 
fected by time as long as the fish were placed on ice 
and measured within 12 hours of capture. Slopes 
were -0.19, or approximately a 1° drop in phase 
angle, for every 5°C increase in temperature. There 
was no effect of time on phase angle on fish iced for 
less than 12 hours. At about 12 hours, juvenile coho 
salmon enter rigor mortis and phase angle mea- 
sures begin to increase. These are important find- 
ings because fishery biologists using BIA can minimize 
error caused by temperature effects by icing fish or by 
trying to keep temperature fluctuations to a minimum 
before BIA measurements. 
Figure 8 
Phase angles for postmortem adult pink salmon ( Oncoryhn - 
chus gorbuscha) (n = 3) measured every 10 minutes for 5 days 
while stored at temperatures <11°C. 
In summary, phase angle reflected the nutritional 
status of six species of fish in fresh and saltwater af- 
ter three to four weeks of starvation and reflected the 
presumed nutritional status of field-caught fish. Re- 
