257 
Abstract — We evaluated measures 
of bioelectrical impedance analysis 
(BIA) and Fulton’s condition factor 
(K) as potential nonlethal indices 
for detecting short-term changes in 
nutritional condition of postsmolt 
Atlantic salmon ( Salmo salar). Fish 
reared in the laboratory for 27 days 
were fed, fasted, or fasted and then 
refed. Growth rates and proximate 
body composition (protein, fat, water) 
were measured in each fish to evalu- 
ate nutritional status and condition. 
Growth rates of fish responded rap- 
idly to the absence or reintroduction 
of food, whereas body composition 
(% wet weight) remained relatively 
stable owing to isometric growth in 
fed fish and little loss of body con- 
stituents in fasted fish, resulting in 
nonsignificant differences in body 
composition among feeding treat- 
ments. The utility of BIA and Ful- 
ton’s K as condition indices requires 
differences in body composition. In 
our study, BIA measures were not sig- 
nificantly different among the three 
feeding treatments, and only on the 
final day of sampling was K of fasted 
vs. fed fish significantly different. 
BIA measures were correlated with 
body composition content; however, 
wet weight was a better predictor of 
body composition on both a content 
and concentration (% wet weight) 
basis. Because fish were growing 
isometrically, neither BIA nor K was 
well correlated with growth rate. For 
immature fish, where growth rate, 
rather than energy reserves, is a more 
important indicator of fish condition, 
a nonlethal index that reflects short- 
term changes in growth rate or the 
potential for growth would be more 
suitable as a condition index than 
either BIA measures or Fulton’s K. 
Manuscript submitted 16 February 2011. 
Manuscript accepted 10 January 2012. 
Fish. Bull. 110:257-270 (2012). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Evaluation of bioelectrical impedance analysis 
and Fulton's condition factor as nonlethal techniques 
for estimating short-term responses 
in postsmolt Atlantic salmon ( Salmo salar ) 
to food availability 
Elaine M. Caldarone (contact author ) 1 
Sharon A. MacLean 1 
Beth Sharack 2 
Email address for contact author elaine.caldarone@ noaa.g ov 
' Narragansett Laboratory 
Northeast Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
28 Tarzweil Drive 
Narragansett, Rhode Island 02882 
2 J. j. Howard Laboratory 
Northeast Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
74 McGruder Road 
Highlands, New Jersey 07732 
Populations of Atlantic salmon ( Salmo 
salar) are broadly distributed across 
the North Atlantic Ocean, repro- 
ducing in coastal rivers of Iceland, 
Europe, northwestern Russia, and 
northeastern North America. Histori- 
cally, native Atlantic salmon ranged 
throughout New England waters, but 
by the late 1880s, they were extir- 
pated from many of the rivers. Cur- 
rently, native populations exist only in 
central and southeast Maine (North- 
east Fisheries Science Center, http:// 
www.nefsc.noaa.gov/sos, accessed July 
2011). A significant decline in these 
populations during the 1990s resulted 
in the listing of the Gulf of Maine 
Distinct Population Segment (DPS) as 
endangered under the United States 
Endangered Species Act (Federal Reg- 
ister, 2009). Hatchery-based restora- 
tion of salmon to this area began in 
1970 and continues today. Although all 
life-stages have been released to the 
rivers, recent emphasis has focused on 
releasing fry and smolts produced in 
the hatchery from field-caught adults 
from the DPS region. Once smolts 
reach the sea, they must adapt to an 
environment and food source radi- 
cally different from their freshwater 
habitats. To evaluate the success of 
these restoration efforts, managers 
need tools to assess whether hatchery- 
reared fish are thriving in the natural 
environment and to assess condition of 
the postsmolt Atlantic salmon popula- 
tion as a whole. 
Growth rate and fat content are key 
measures of condition in fish. During 
a fish’s early life-history stage, rapid 
growth rates increase the probability 
of survival and recruitment, primar- 
ily through decreased vulnerability 
to predation and starvation (see re- 
view by Fonseca and Cabral, 2007). 
Fat, the primary energy repository 
in marine fish, increases when food 
intake exceeds metabolic needs and 
decreases during food-limited times 
when it provides energy for main- 
tenance, growth, and reproduction 
(Shulman and Love, 1999; Jobling, 
2001). Growth rates of fish caught in 
the wild are often estimated by us- 
ing nucleic acid analysis (the ratio of 
RNA to DNA) or otolith microstruc- 
ture analysis (Chambers and Miller, 
