294 
Fishery Bulletin 114(3) 
05 " 
E 
3 : 22 
C 
'a) 
2 18 
Q. 
a: 
Fed 
— Fasted 
-- Refed 
i 
a 
^ I 
\<i 
\ 1 
A 
ab 
9rb 
O) 
E 
D) 
ZL 
C 
B 
O 
Q. 
Fed 
Fasted 
i 
Refed 
1^ ^ 
2 ./ I J 
i 
i'i 
IT T 1 r 
-J I I I I I I I I 
0 3 6 9 12 15 18 21 24 27 
Day 
to 
E 
(/> 
Cl 
-^1 
c5) 
c 
LL 
33 
o 
19 
!| 1 
5 
C 
3 
6 
9 12 15 18 21 
Day 
Figure 3 
(A) RNA/protein (pg/mg); (B) DNA/protein (pg/mg) and 
(C) IGFl (ng/mL plasma) values of postsmolt Atlantic 
salmon {Sal/no salar) reared in the laboratory at 12°C. 
Values are mean values (±standard deviation [SD]) for 
each sampling day. Fish were either fed ad libitum, 
fasted, or refed (fed after 11 days of fasting). Within a 
sampling day, food treatments showing a common su- 
perscript, or without superscripts, do not differ signifi- 
cantly (Tukey’s HSD multiple range tests). Where error 
bars would overlap, data are offset to facilitate viewing. 
The arrow indicates the day when food was introduced 
to the refed group. For fed and fasted fish, n=4 for each 
sampling day. For refed fish, n=22 for day 11, n=5 for 
days 15, 19, and 23 and n=7 for day 27. 
eluded RNA/DNA and IGFl (Table 3). Because RNA/ 
DNA was highly correlated with the other biochemical 
terms, we also tested all combinations of the remain- 
ing 4 terms after eliminating RNA/DNA (15 models). 
The best candidate for a growth rate model from this 
grouping included RNA/pro, DNA/pro, and IGFl, and 
was essentially identical in predictive capability and 
mathematically equivalent to the model containing 
RNA/DNA and IGFl (Table 3). 
Summary 
RNA/DNA ratios and recent growth rates of fed fish 
increased throughout the study and were highly cor- 
related. Fed and fasted feeding treatments could be 
differentiated by RNA/DNA values after 11 days of 
fasting, and on an individual basis, significant decreas- 
es in RNA/DNA values were observed after 7 days of 
fasting. Growth rates and RNA/DNA values of previ- 
ously fasted fish increased rapidly beginning 4 days 
after refeeding. The intercept from regressing growth 
rate on RNA/DNA was greater in refed fish than in 
continually fed fish, whereas the slopes were parallel. 
In the fasted group, the rate of weight loss remained 
fairly constant throughout the experiment and RNA/ 
DNA values decreased. 
In all 3 feeding treatments, RNA/pro values showed 
similar trends to those of RNA/DNA values; however, 
there was less statistical differentiation between the 
feeding treatments on most sampling days. Overall, 
fasted fish had significantly greater DNA/pro values 
(smaller cells) than fed fish, yet feeding treatments 
within a day could not be distinguished on this basis. 
Mean IGFl values increased in fed fish but remained 
constant in fasted fish owing to inconsistent individual 
responses to fasting. Based on repeated measurements 
of individuals, IGFl values responded rapidly (4 days) 
to refeeding. Owing to high daily variability, feeding 
treatments within a sampling day could not be distin- 
guished with this index. A positive and significant rela- 
tion was found between IGFl and growth rate. 
Of the 31 models tested, the best-fit growth rate 
model included RNA/DNA and IGFl with a coefficient 
of determination (r^) =0.73. 
Discussion 
The goal of our research and its companion study 
(Caldarone et ah, 2012) was to identify physiological 
indices that could be obtained by nonlethal means 
and that would respond rapidly to short-term changes 
(4-23 days) in the nutritional state (feeding and fast- 
ing) of individual postsmolt salmon. The response time 
of an index allows investigators to match the index to 
environmental parameters on relevant temporal and 
spatial scales. Of the four indices we measured in this 
study, RNA/DNA was the most highly correlated with 
short-term growth rate. In sexually immature fish, an 
index that reflects protein production should be appro- 
