Freshwater environment affects growth rate and muscle fibre recruitment in seawater stages of Atlantic salmon (Salmo salar L.)
Ian A. Johnston1,*,
Sujatha Manthri1,
Richard Alderson2,
Alistair Smart3,
Patrick Campbell2,
David Nickell4,
Billy Robertson3,
Charles G. M. Paxton5 and
M. Louise Burt5
1 Gatty Marine Laboratory, School of Biology, University of St Andrews, St
Andrews, Fife, Scotland, KY16 8LB, UK
2 BioMar Ltd, North Shore Road, Grangemouth Docks, Grangemouth, Scotland,
FK3 8UL, UK
3 Marine Harvest Scotland Ltd, Craigcrook Castle, Edinburgh, Scotland, EH4
3TU, UK
4 Roche Vitamins Ltd, Heanor, Derbyshire, England, DE75 7SG, UK
5 Research Unit for Wildlife Population Assessment, School of Mathematics
and Statistics, University of St Andrews, St Andrews, Fife, Scotland, KY16
9LZ, UK
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Fig. 1. The temperature regime experienced by the ambient (open circles) and heated
(filled circles) treatment groups of Atlantic salmon.
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Fig. 2. The growth performance of fish from the ambient (open circles;
N=206) and heated (filled circles; N=298) treatment groups
of Atlantic salmon. The values represent means ± S.D. NS, no
significant difference between treatments.
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Fig. 3. Fit of the growth model to the observed data of body mass in seawater. In
the figure, y is plotted against x2, where
y=(Mt+t'1-ß-Mt1-ß)/(1-ß)
and x2=t'(T-Tavg). The
variables are defined in Table
2. Black dots represent observed values for the ambient group, red
dots represent observed values for the heated group, and the fitted values of
y from model 5 are shown in green. The values have been offset
slightly along the x-axis so that they can be seen more clearly.
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Fig. 4. Histograms of y for each growth period (i.e. period 1 is between 4
April 2000 and 31 May 2000, period 2 is between 31 May 2000 and 10 July 2000,
etc.; see text for further details).
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Fig. 5. The number of fast muscle fibres per trunk cross-section (FN) for
the ambient (open circles) and heated (filled circles) treatment groups of
Atlantic salmon. (A). The relationship between FN and age
post-fertilisation for the randomly sampled fish. The numbers in brackets
represent the number of fish sampled for the ambient and heated groups,
respectively. The arrow shows the age at which smolts were transferred to
seawater cages (SWT). (B) The relationship between FN and the total
cross-sectional area (TCA) of fast muscle at the level of the first dorsal fin
ray. The values represent means ± S.E.M. Fish were selected at random,
except for the last two samples (box), which represents a selection of the
largest individuals available in each cage. The numbers in brackets represent
the number of fish sampled for the ambient and heated groups,
respectively.
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Fig. 6. The distribution of muscle fibre diameter in the fast myotomal muscle of
Atlantic salmon: (A) the final sample of the ambient treatment group sampled
988 days post-fertilisation; (B) the final sample of the heated treatment
group sampled 997 days post-fertilisation. Smooth distributions were fitted to
800 measurements of fibre diameter per fish using a nonparametric kernel
function. The broken lines represent the probability density for individual
fish, and the solid line represents the mean probability density function for
each group.
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Fig. 8. The mean probability density of muscle fibre diameter for heated (solid
line) and ambient (dashed line) treatment groups for the first (A) and last
(B) seawater samples taken in July 2000 and August 2001, respectively. The
shaded polygon represents 100 bootstrap estimates of the combined populations
of ambient and heated fish, and the dotted line represents the mean
probability density function of the pooled groups. Regions where the mean
probability density function fell outside the shaded polygon provided
graphical evidence for a difference between the populations.
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Fig. 9. The relationship between maximum fibre diameter (Dmax)
and (A) age post-fertilisation and (B) body mass for the heated (filled
circles) and ambient (open circles) treatment groups of Atlantic salmon.
Values represent means ± S.E.M. The number of fish sampled is as in
Fig. 5A.
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Fig. 10. The rate of muscle fibre hypertrophy of fast muscle fibres between
successive sample points plotted against seawater growth in Atlantic salmon
from the heated (filled circles) and ambient (open circles) treatment groups.
The rate of hypertrophy has been plotted at the midpoint of the time period
over which it was calculated. Values represent the mean of the difference
between the observed fibre diameter and the mean value of the fibre diameter
in the preceding sample.
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Fig. 11. The nuclear content of isolated muscle fibres. (A) A fast muscle fibre
stained with the fluorescent DNA stain Sytox green. The confocal image
represents a projection of 1 µm sections through the fibre. (B) The number
of myonuclei in single muscle fibres of 1 cm length in relation to muscle
fibre diameter. Open circles represent the ambient group and filled circles
represent the heated group. The lines represent linear regressions (see text
for details).
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Fig. 12. (A,B) Immunohistochemistry showing sections of salmon fast myotomal muscle
double-stained with primary antibodies to laminin and c-met using Cy-3 as the
secondary antibody and Sytox green as a nuclear counterstain. Nuclei are
stained green (white arrowheads), and c-met+ve cells (yellow
arrows) and the basal lamina are stained red.
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© The Company of Biologists Ltd 2003
) in fish that had completed fibre recruitment
in the June 2001 samples. Filled and open symbols represent the heated and
ambient treatments, respectively. A first-order linear regression was fitted
to the data (r2=0.35;