News & Views Fish Nutrition Research
Algal carotenoids may be more efficiently digested by Atlantic salmon: study

Utilization of dietary carotenoids for farmed salmon may be optimized by combining algal carotenoid with different oil sources that contain more oleic acid, such as canola, and less saturated fatty acids, such as tallow, according to the article, “Dietary fatty acid composition affects the apparent digestibility of algal carotenoids in diets for Atlantic salmon, Salmo salar.”

“This study continues to demonstrate the utility of algal carotenoids as natural pigment alternatives for farmed salmon, particularly beneficial when combined with different oil sources. The combined impact of feed intake and digestibility on carotenoid utilization from Atlantic salmon diets may demonstrate improved performance and pigmentation in larger scale studies,” said Emily Courtot et al. 

Carotenoids, which are fat-soluble, enhance the natural pigmentation of animal flesh. Astaxanthin (Axn) is most commonly used in salmonid. It has “highly variable” digestibility in salmonids, which swings between 20 to and 60 per cent.

Wild salmon have pink flesh because of natural diets containing astaxanthin.

Farmed salmon tend to have light-colored flesh. Supplementation of carotenoids in diet creates the flesh colour the consumers expect.

The authors compared the feed intake, as a measure of diet palatability, and apparent digestibility (AD) of Axn between the two diets containing either synthetic or algal carotenoids, a natural alternative. 

They also assessed the effect of manipulating dietary lipid sources on Axn digestibility, using commonly available products with different fatty acid compositions, such as canola oil, tallow and poultry oil. These have significantly different fatty acid composition, which was reflected in the experimental diets.

This experiment contained four diets fed to juvenile Atlantic salmon in tanks for two weeks. All were formulated to contain two oil sources: fish oil at six per cent in addition to 10 per cent complementary lipid source.

“This study showed that neither Axn sources nor dietary lipid sources affected the palatability of the diets. Moreover, algal carotenoids had a higher AD than synthetic carotenoids, which suggested that they may be more efficiently digested by Atlantic salmon,” the authors cited.

The team represented the Commonwealth Scientific and Industrial Research Organization in Australia and the Center for Research on Environmental Ecology and Fish Nutrition of the Ministry of Agriculture, Shanghai Ocean University in China. The article was published on Aquaculture Research.

At present, 95 per cent of the aquaculture industry uses synthetic Axn. If market preferences are heeded, however, this share might start contracting as consumers have started showing partiality for natural and more sustainable food products. Naturally-produced Axn also has a trait that could very easily win over the consumers in this cluster. It was recently established that natural astaxanthin may be 20 times more powerful as an antioxidant.

 Production costs make algal carotenoids much more expensive than its synthetic counterpart.