Marine algae for salmon feeds

Alger4laks was part of the MARINALGAE4aqua project and investigated the suitability of micro- and macroalgae as components in feeds for salmon. Nannochloropsis oceanica and Tetraselmis chuii were selected in this project because they are photosynthetic algae that are approved by EFSA for use in food and feeds. A new prebiotic product from the macroalga Laminaria sp. was also studied in the project. Before the aquafeed industry starts to incorporate algae into salmon feeds, processing technology that can break the algae cell walls to make the nutrients bioavailable to Atlantic salmon should be tested. In the project, extrusion was chosen as a thermo-mechanical process for breaking the cell walls of Nannochloropsis and Tetraselmis because it is an existing method that can be easily scaled up and used for processing larger amounts of algae biomass. In addition, the feeds with microalgae were tested together with various additives to understand their ability to improve the digestive capacity and utilization of the feeds by Atlantic salmon. The only study conducted in this project on macroalgae examined the potential of an oligosaccharide derived from Laminaria as a prebiotic for salmon. A feeding trial with post smolt salmon fed a control feed based on marine raw materials and four different test diets with 30% inclusion of whole and broken microalgae showed that the pretreatment can impart better growth, especially in fish fed Nannochloropsis. The pretreatment of Tetraselmis led to a significant increase in gene expression for antioxidant capacity in the liver. Two feeding experiments were also carried out to investigate growth, feed utilization, and health of post-smolt salmon fed microalgae, plant protein concentrate and rapeseed oil as partial substitutes for fishmeal and fish oil. For each of the two studies, four experimental feeds were made; one control feed based on plant protein and rapeseed oil, two feeds with 7.5 and 15% processed algae and one feed with 15% inclusion of unprocessed algae. The results showed that Nannochloropsis incorporation led to reduced growth, feed conversion efficiency as well as digestibility of protein and fat, especially at the highest inclusion level. The health status of the different feeding groups was similar; based on antioxidant and immune genes, and can be interpreted as there are no negative effects of feeding Nannochloropsis (7.5% and 15% in feed). On the other hand, the results of the growth, feed utilization and chemical composition of the fish fed Tetraselmis supported the findings from the Nannochloropsis study. In addition, a fillet storage study showed that salmon fed 15% Tetraselmis had lower lipid oxidation, which indicated better quality of the fish fillet. Inflammatory genes, antimicrobial peptide genes and intestinal micromorphology did not reveal any adverse effects of the two microalgae. Nannochloropsis showed a greater potential as a feed ingredient for fish which accumulated a good amount of PUFAs. Therefore, the microalga was selected for a subsequent study to investigate the effect of commercially available additives on digestibility and utilization of feed containing 10% processed microalga. The additives did not give any desired effect on digestibility and feed utilisation at the inclusion levels tested in the experiment. Finally, a 7-month growth trial was conducted with salmon to investigate the efficacy of feeds containing 7.5% Nannochloropsis on the fish that has grown up to the slaughter size. There was no difference in the growth between salmon fed the alga and the control feed. There was no difference in fillet quality based on pigmentation and fat. A study with the macroalgae-derived oligosaccharide at 0.5 or 2.5% in feeds indicated that the prebiotic does not affect the growth and feed utilization in the fish. Nevertheless, at the low level the product helped in favouring bacteria with butyrate producing genes. In short, this project has shown that Nannochloropsis has a greater potential as a feed ingredient than Tetraselmis, but both microalgae can be incorporated up to 7.5% in feeds for salmon. Tetraselmis in salmon feeds can have positive effects on the shelf life of fish after slaughter and have also shown beneficial effects on gene expression associated with antioxidant capacity and health in the liver of salmon. Extrusion as a preprocessing contributed only to a moderate improvement in nutrient utilization. New products from macroalgae of the genus Laminaria can be added to salmon feeds to impart a prebiotic effect on salmon gut microbiota.

Økt kunnskap om bruk av marine mikro- og makroalger vil bidra til økt bærekraft for norsk akvakulturnæring. Bruk av fotosyntetiske ingredienser fremstilt fra karbondioksid og sollys, vil bidra til å redusere klimaavtrykket av både akvafôrindustrien og akvakulturnæringen. Bruk av ingredienser fra første trofiske nivå i den marine næringskjeden som erstatning for fiskemel og fiskeolje, vil i tillegg ha stor fordel markedsmessig ved salg av norskproduserte akvakulturprodukter. I løpet av prosjektforløpet, videreutviklet studentenes og ansattes kvalifikasjoner og sørget for at de klarer å takle forskningsutfordringer.

Alger4laks (part of MARINALGAE4aqua, a COFASP ERA NET project) intends to demonstrate the suitability of the micro- and macro-algae as components of feeds for Atlantic salmon. The project MARINALGAE4aqua aims to improve the bio-utilisation of marine algae as a sustainable feed ingredient, to increase efficiency and quality of aquaculture production. The aquafeed industry is actively seeking new ingredients for feeds of major farmed species, including Atlantic salmon. Sustainable protein and lipid sources are essential for future aquafeeds. The extant information indicates that the digestibility of algae depends on their variety, and the algae have to be processed to improve their nutrient bioavailability. Furthermore, inclusion of feed additives may ensure better utilization of the algae by the farmed fish. In addition, algal inclusion may improve fish growth and health. The efficacy of algae as suitable fishmeal and fish oil replacers will be demonstrated through feeding trials on Atlantic salmon employing the specially formulated feeds.