Several advantages with purified feed oil
New trials show that salmon fed feeds containing purified fish oil are healthier and have a firmer fillet, and that the feed is also utilised better. This should definitely be included in the evaluation of whether or not it is profitable to use purified fish oil in salmon feeds.
Scientists at Nofima Marin have implemented the trials using Atlantic salmon on commission for Pronova BioPharma. The trials took place at Gildeskål Research Station in the period from July 2007 to December 2008, from the smolt phase through to salmon that had reached the slaughter size. The trials studied whether growth, health effects and fillet quality were influenced by whether the feed contained purified or unpurified fish oil.
Positive growth results
"The two feed types were identical apart from the fact that standard commercially available fish oil was replaced with the same oil purified in accordance with Pronova BioPharma’s method," says Scientist Jan Olli.
The trials showed a trend of better growth and feed utilisation among salmon that consumed the feed containing purified oil. This was particularly the case during periods of high growth when both the growth rate and feed utilisation rate were significantly better for the fish that received the feed containing purified oil.
Better fish welfare?
Another important finding was that the salmon that received the feed containing purified oil appeared to better tackle the handling stress during the slaughtering process – measured as a delayed pH reduction after killing. Other stress markers showed the same tendencies.
"In today’s market, where the focus on fish welfare has become steadily more important, this is an extremely interesting find," says Scientist Turid Mørkøre at Nofima Marin.
Bente Ruyter, a Professor and Senior Scientist at Nofima Marin, has headed the measuring of health effects in the study, which have been carried out in collaboration with Jyväskylä University in Finland and the Norwegian School of Veterinary Science. She points out that the content of impurities in today’s fish is far lower than the EU’s maximum limits and there is really no doubt that fish is very healthy and important for our diet.
"But we should not omit the fact that the impurities will be reduced when the fish oil used in the feed is purified to remove these," says Ruyter. "In this way, the salmon become even healthier food. Even though there are not significant differences in the measurements of health markers in the blood, liver, intestine and fatty tissue, the salmon fed with purified fish oil score on average slightly better."
Want to study the causal connections more closely
All the fish in the trial maintained a good red colour and firmness, but there was a tendency that fish that received the feed containing purified oil had a firmer texture. The difference in texture was most pronounced after freezing. The proportion of salmon with soft texture was then halved in comparison to the fish that received unpurified oil.
"These are interesting results, which show that the faster growth among salmon that received feed containing purified fish oil was not at the expense of the fillet quality," says Mørkøre, adding: "The finds from this comprehensive study indicate that we have touched on something that we still have not understood the full scope of yet. But it looks like we achieve significant gains by reducing the level of impurities in the feed."
"The positive signals with purified feed make it extremely interesting to study the causal connections of our finds in further studies," says Ruyter. "It will also be of relevance to study whether the same effects apply to other fish species for which feeds containing fish oil are utilised."