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The fatty acids in the salmon lipid stores reflects the feed
fatty acid composition. Accordingly, when the salmon is fed
vegetable oils as a substitute for fish oils, the fatty acid
profile changes in the fish. Vegetable oils may also affect the
salmon’s lipid metabolism.
"We have found 10 genes coding for proteins which are known to
be important for the uptake, transport and metabolism of fatty
acids in the cells. This can help us to understand how the lipid
metabolism is regulated by the salmon, thus telling us what happens
when we change the composition of fatty acids in the feed", says
Dr. Bente E. Torstensen, senior researcher in the Aquaculture
Nutrition Research Programme at NIFES.
"These genes may prove to be an important tool in helping us
understand why inclusion of vegetable oil affect the fish
metabolism and thereby being able to determine the quantity and
type of vegetable oils to be used in the feed in order to achieve
the optimal growth and wellbeing of the salmon", says
Torstensen.
Gene identified for the first time in salmon
As part of the study, Atlantic salmon were given feed containing
either 100% fish oil (control) or 100% vegetable oils. The fish
were fed for 27 months until their weight was around 4.5 kg. Key
genes involved in lipid metabolism were identified in several
organs. Among the findings was the FABP11 gene which was expressed
in the visceral fat depot, myosepta between the muscle fibres and
in the heart.
"This is the first time the expression of this gene has been
shown in Atlantic salmon. It has an important function in the
salmon’s lipid storage cells, either in the storage process
or in the transport of fatty acids out of the cell", says
Torstensen.
The exact function of FABP11 in the fatty tissue of mammals is
also not fully understood, but it is thought to have a key role in
the transport of fatty acids out of the adipose cell.
"In this study the RNA expression of FABP11 was down-regulated
when the salmon were fed vegetable oils. The amount of storage fat
was reduced in both the salmon’s visceral fat tissue and
muscle".
Less or more energy from vegetable oils?
Salmon cells produce energy when fatty acids are broken down in
the mitochondria (cellular organelles which provide the cell with
energy) in a reaction called beta-oxidation, or fatty acid
catabolism.
"We have identified several genes coding for proteins which a
play key role in this reaction. A number of these genes were
down-regulated in salmon fed feed with 100% vegetable oils. This
can lead to a lower energy production and was in our study related
to a slight reduction in the fatty acid catabolism capacity in
white muscle", says Torstensen.
Klick here for more information about the scientific paper.
This project was funded by the Norwegian Research Council
(project number: 158930/I10). The feeding experiment was part of
the project “Researching Alternatives to Fish Oils in
Aquaculture” (RAFOA), Q5RS-2000-30058 funded by the EU Fifth
Framework Programme.
Collaborating partners:
Nofima Marin, the Norwegian University of Life Sciences, the
University of Oslo.
Contact person:
Bente E. Torstensen,
Aquaculture Nutrition Research Programme.
Telephone: (+47) 41462894
E-mail: bto @nifes.no
Additional reading:
"Farmed salmon is still an excellent source of omega-3"
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Facts:
What is DNA and gene
expression?
All cells in the body
have a cell nucleus which contains DNA. The DNA contains genetic
sequences which define the structure of different proteins with
different functions. For a protein to be created, the DNA must
undergo a process whereby the genetic sequences are transcribed to
mRNA, which is transported out of the cell nucleus. The term
“genetic expression” means the amount of mRNA in a cell
or a tissue at a given time. When mRNA is transported from the cell
nucleus the transcription unit is translated to a protein. When we
say that a gene is up-regulated, more of a specific mRNA that codes
for a protein is produced. More of this protein will be produced,
such as an intake protein, a transport protein or an enzyme. This,
in turn, can affect processes in the cell and in the body.
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