288 
NOAA 
National Marine 
Fisheries Service 
Fishery Bulletin 
established 1881 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Evaluation of nucleic acids and plasma l€F1 
levels for estimating short-term responses 
of postsmolt Atlantic salmon iSatmo salary 
to food availability 
Email address for contact author: brian.beckman@noaa.gov 
Abstract — We evaluated 4 potential 
indices obtained by nonlethal sam- 
pling for use in determining nutri- 
tional state and short-term growth 
rate in postsmolt Atlantic salmon 
{Salmo salar): the ratio of RNA to 
DNA, both RNA and DNA normal- 
ized to protein, and plasma levels of 
insulin-like growth factor 1 (IGFl). 
Fish reared in the laboratory for 
27 days were fed, fasted, or refed. 
Short-term growth rates (7 to 23 day 
intervals) were calculated on a wet- 
weight basis. RNA/DNA values were 
highly correlated to growth rates, 
responded rapidly to changes in food 
availability and were the best able 
to consistently distinguish between 
the fasted and fed treatments. RNA/ 
protein values were also well cor- 
related with growth rate; however, 
within any one sampling day, feed- 
ing groups could not be differentiat- 
ed with this index. DNA/protein in- 
creased during fasting but was nei- 
ther strongly correlated with growth 
rate nor an accurate discriminator of 
nutritional state. IGFl values were 
positively correlated with growth 
rates and responded rapidly with 
refeeding but changed little during 
the 3 weeks of fasting — a result that 
may have been influenced by sam- 
pling serially. We propose that RNA/ 
DNA is a useful nonlethal technique 
for estimating recent growth rates 
and for identifying the nutritional 
condition of individual postsmolt At- 
lantic salmon exposed to short-term 
changes in food availability. 
Manuscript submitted 15 May 2015. 
Manuscript accepted 31 March 2016. 
Fish. Bull. 114:288-301 (2106). 
Online publication date: 3 May 2016. 
doi: 10.7755/FB.114.3.3 
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. 
Elaine M. Caldarone' 
Sharon A. MacLean' 
Brian R. Beckman (contact author)^ 
' Narragansett Laboratory 
Northeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
28 Tarzwell Drive 
Narragansett, Rhode Island 02882 
^ Environmental and Fisheries Sciences Division 
Northwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
2725 Montlake Boulevard East 
Seattle, Washington 98112 
The ability to measure the growth 
rate of a fish can be a powerful tool 
for evaluating the survival potential 
of an individual. The ability to assess 
the nutritional state of a fish, wheth- 
er the animal is feeding or fasting 
and for how long the fish has been in 
that state (hours to days to weeks) 
is also highly desirable information 
because variation in nutritive state 
leads to variation in growth rate. 
Currently, there are a limited num- 
ber of nonlethal techniques avail- 
able for estimating growth rates or 
nutritional state (or both) in field- 
caught juvenile fish. Longitudinal 
cohort analysis is a direct approach 
to assessing changes in size (growth); 
however obtaining multiple samples 
of the same cohort in the field can 
be challenging. Biochemical indices 
that indirectly yield estimates of 
growth rate or nutritional state have 
the advantage of providing estimates 
within a single sampling. This point 
estimate allows an investigation of 
the connectivity between nutritional 
state and environmental parameters 
on relevant temporal and spatial 
scales. 
In this study we evaluated 4 poten- 
tial biochemical indices of short-term 
growth-rate or nutritional state in 
postsmolt Atlantic salmon (Salmo sa- 
lar): the ratio of RNA to DNA (RNA/ 
DNA), both RNA and DNA on a pro- 
tein basis (RNA/pro and DNA/pro, 
respectively) and circulating plasma 
insulin-like growth factor 1 (IGFl). 
Considerable effort has been directed 
toward hatchery-based restoration of 
Atlantic salmon to 8 rivers in Maine, 
where the population has been listed 
as endangered since 2009 under the 
United States Endangered Species 
Act (Federal Register, 2009). Restora- 
tion managers require tools to both 
assess whether hatchery-reared fish 
are thriving in the natural environ- 
ment and to assess the condition of 
native postsmolts. Identifying a mini- 
mally invasive, nonlethal method to 
provide an index of growth rate or 
nutritional state in postsmolt Atlan- 
