Caldarone et al.: Biological indices of growth rate and nutritional state of Salmo solar 
299 
fasting, IGFl and growth, IGFl and refeeding) were 
due to the induction of different suites of binding pro- 
teins and how these proteins may have affected circu- 
lating IGFl levels differently from those of other stud- 
ies. Shimizu et al. (2009) demonstrated a significant 
increase in 41kDa IGFBP of fasting fish in response 
to refeeding; perhaps the IGFl increase we observed 
in our individual refed fish was modulated by changes 
in circulating IGFBP levels. The fact that IGFl levels 
of fasted fish did increase in response to refeeding and 
that the overall relation of IGFl to growth was positive 
and significant gives us confidence that IGFl responds 
to changes in nutrition and growth. The use of IGFl 
measures has been demonstrated in several ecological 
studies of juvenile salmonids where differences in IGFl 
levels have been observed in fish reared in different ar- 
eas (Bond et al., 2014; Daly et ah, 2014; Ferriss et al., 
2014). However, we suggest that the specific response 
of IGFl and IGFBPs to fasting, feeding, and growth, 
in combination with acute or chronic stress, should be 
investigated. 
Of the indices reported here (RNA/DNA, RNA/pro, 
DNA/pro, IGFl) and in Caldarone et al. (2012) (Ful- 
ton’s K, BIA), RNA/DNA was the most suited for es- 
timating recent growth rates and identifying the nu- 
tritional condition of our individual postsmolt Atlantic 
salmon exposed to short-term changes in food avail- 
ability. Removing muscle samples with a biopsy punch 
for RNA/DNA analysis did not result in any mortalities 
and did not appear to inhibit growth of the fish, as evi- 
denced by the rapid increase in growth rates of refed 
fish soon after a muscle sample was taken. The short 
response time of RNA/DNA (4-8 days) in individual 
fish to both positive and negative changes in food avail- 
ability would allow researchers to investigate linkages 
between environmental variables and nutritional state 
on ecologically relevant scales. With the addition of a 
temperature calibration, estimates of growth rates in 
the field at a variety of temperatures could be calcu- 
lated with RNA/DNA values 
Acknowledgments 
The authors would like to thank E. Baker, and K. 
Fredrick for assistance in aquarium setup and tem- 
perature control, M. Prezioso and J. St. Onge-Burns 
for help in rearing the salmon, K. Cooper for running 
the IGFl analyses, and the University of Rhode Island 
Graduate School of Oceanography for the use of Blount 
Aquarium. 
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