Scientist Katerina Kousoulaki tested algae meal from heterotrophic algae in the feed of farmed salmon.

Scientist Katerina Kousoulaki tested algae meal from heterotrophic algae in the feed of farmed salmon.

Fish oil is an ideal source of omega-3 in salmon feed, but the capacity to produce farmed salmon using fish oil as the main source of omega-3 in feed is limited, if the farmed salmon itself is to remain a rich source of omega-3. This means that the salmon feed industry needs access to large volumes of new ingredients that contain omega-3. Experiments at Nofima have shown that heterotrophic algae can fully replace fish oil in feed used for small salmon.

“We need further sources of omega-3, and heterotrophic algae are one of very few real possibilities at the moment. The algae meal that we have tested contains nutrients that salmon need. We have managed to release and preserve the important nutrients through the process of manufacturing the feed, and this is a necessary condition for the use of this ingredient,” says scientist Katerina Kousoulaki.

Kousoulaki works at the food research institute Nofima and, together with colleagues and the Feed Technology Centre in Bergen, has tested algae meal from heterotrophic algae in the feed of farmed salmon.

SINTEF, the largest independent research organization in Scandinavia, has shown that heterotrophic algae such as the one tested by Nofima can be produced at a density of 160-180 gram dry weight per liter of culture, while phototrophic algae can be produced at up to 1-4 gram dry weight per liter. This means that much less space is needed. Additionally, the productivity for heterotrophic algae is approximately 10 gram/l when grown in large reactors, while it is 0.06 gram/l for phototrophic algae.

Nofima signed a collaboration agreement with Alltech in 2012. One of the world’s largest companies in the field of animal health and nutrition, Alltech wanted Nofima to test one of its algae meals in fish feed. The work presented here is one result of the collaboration, where Nofima tested how the algae meal affects salmon health, performance, and nutrition.

More than a quarter of the fat in algae is the healthy marine omega-3 fatty acid DHA, which is up to three times more than in fish oil. The alga in this meal trial – now being produced commercially by Alltech in the US – is a member of the Schizochytrium family, and is extremely rich in omega-3. The algae have not been subject to gene modification.

The normal content of fish oil in commercial feed is around 11%. The meal was added to salmon feed at levels of 0 (control), 1%, 6% and 15% of the feed. The amount of fish oil in the feed was correspondingly reduced, from 15% to 0%. Hence the feed with 15% algae meal contained no fish oil.

The alga-based feed was given to small salmon weighing approximately 200 grams in ponds for 12 weeks. All fish had more than tripled their weight at the end of this period, irrespective of the feed they had received. The salmon increased their intake of food when it contained algae, which suggests that the algae do not inhibit appetite.

The amount of the long-chained marine omega-3 fatty acids in the fillets was higher in salmon that had received the algae meal than it was in salmon that had been given fish oil as their only source of these fatty acids. The digestibility of protein was equal in all feeds, and the digestibility of fat was highest for the feed with 1% algae meal.

Micromatrix analysis, considered to be a reliable measurement method for effects on health, showed that the feeds had no negative effects on health.

Nofima has also studied whether the algae meal was suitable for ensuring a high technical fillet quality of the salmon. Salmon fillets from fish given feed that contained algae tested just as good as those from fish given exclusively fish oil. The texture of the fillets, for example, was just as firm, as was drainage of water. The amount of gaping in the fillets was also the same.

Nofima is now continuing at the Feed Technology Centre in Bergen with optimizing the algae meal in feed and improving the way in which it is processed. The algae meal is also to be tested in trials as a possible whole-life feed for salmon.

(Editor’s note: the following question has generated the clarifications to this article below):

(from Neil Glasgow)
I am curious to find out how a Feb 12, 2015 article about SINTEF and fish oil could quote their apparent lab scale Heterotrophic algae growth system as achieving 160-180 grams dry weight per liter but a large Heterotrophic reactor only produces 10 gram/lt. That appears to be 16 to 18 times large scale production. Please provide a fact check. If it’s correct, I want to invest in the SINTEF process.

(from Dr. Katerina Kousoulaki)
The density numbers you mention were published in different conferences and they seem correct (160-180g/l) but on the high range. However, the productivity number in gram/l is missing the time parameter and as you write it is actually again a density measure and more than 10 times lower than the number you present above.

The microalgae that I used were produced by Alltech Inc who again would be the appropriate actor to answer your question regarding the species that I used in my research. My expertise is more related to downstream processing of microalgae biomass and development of products for food and feed applications.

p.s. This article was written by our journalist based on an internal report of my research and production data from SINTEF. SINTEF tested those algae and it will be more appropriate to get the answer you are looking for from them.

(from Alltech’s Becky Timmons)
I cannot speak for other groups’ production at any scale, as it will always be dependent on a large variety of factors. We currently produce two types of heterotrophic algae and our harvest density is in the 100-150g/l range depending on the species of algae and the specific endpoint that we want to achieve.