Using Vegetable Oils in Farmed Fish Diets09 July 2012
Using fishmeal to feed to fish in aquaculture fisheries could prove to be unsustainable in the long run as the aquaculture industry grows and ocean fish stocks diminish, write Chris Harris.
Hence alternatives such as vegetable oils or animal fats could have to be substituted for fish oils in feed.
Research by Dr Shymalie Sendheera from Deakin University in Australia and the Ocean University in Colombo Sri Lanka found that it is possible to substitute fish oils with vegetable oils and that they had a remarkable effect on the development of fatty acids in the fish.
The research questioned the effect of using vegetable oils because they contained more omega 6 than fish oils have large quantities of the C18 PUFA.
Dr Sendheera presenting her findings at the recent Aquaculture UK exhibition and conference in Aviemore, said that while this might not be good for humans, fish can form long chain PUFAs ( mainly EPA, Eicosapentaenoic acid, DHA, Docosahexaenoic acid, and ARA, Arachidonic acid ) if they are supplied with dietary precursors ALA and LA (Alpha-linolenic acid and linoleic acid).
She said that they had discovered that the fish are able to change the medium chain PUFAs into long chain PUFAs and they also found that micronutrients such as Vitamin B6 (pyridoxine) can affect the lipid metabolism.
In the research to discover if and how Vitamin B6 modulates the fatty acid metabolism in fish, rainbow trout were fed canola and linseed oil as alternatives to fish oil with varying concentrates of pyridoxine.
The feeding trial was carried out over a period of 60 days and samples were taken from the fish faeces and from whole fish and fish fillets.
While the research found no significant changes in growth, performance, feed utilisation efficiency and body composition, the fillets showed a high concentration of Omega 3 fatty acids.
Dr Sendheera said that the was an increasing trends towards neo-genesis of fatty acids with the conversion of fatty acids to long chain fatty acids and what appeared to be a desaturation of fatty acids or an elongation of the fatty acids.
"The relationship between dietary supplementation of pyridoxine and fatty acids was evident," she said.
She said the addition of Vitamin B6 worked with non-fish oils in the diet and it highlights the potential for vegetable oils in the diet of farmed fish.