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 salmons 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 salmons 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 salmons 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.
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