Protein-rich co-product a promising alternative to fishmeal in aquaculture diets
Researchers from Dartmouth College have developed a more sustainable feed for aquaculture by using a marine microalgal co-product as a feed ingredient. The study is the first of its kind to evaluate replacing fishmeal with a co-product in diets designed specifically for Nile tilapia. The results are published in the open access, PLOS ONE.
To address the environmental sustainability concerns regarding aquafeeds, the Dartmouth team has been developing sustainable feeds for Nile tilapia, and examining the effectiveness of replacing fishmeal and fish oil with different types of marine microalgae. Marine microalgae are excellent sources of essential amino acids, minerals, vitamins, and omega-3 fatty acids, and can therefore, meet the nutrient requirements of fish. Omega-3 fatty acids are not only important for maintaining fish health, but also have neurological, cardiovascular and anti-cancer benefits to humans.
The Dartmouth team has been looking into replacing fishmeal with a marine microalgal (Nannochloropsis oculata) co-product, which is rich in both protein and omega-3 fatty acids, including eicosapentaenoic acid, that are essential to fish growth and quality. The co-products are left-over algae meal, once the oils have been extracted from commercially-grown algal biomass to manufacture biofuels and nutraceuticals. The co-product is available on a commercial scale and continued increases in supply are expected. The results obtained indicate that the co-product shows promise in replacing conventional protein ingredients in tilapia feeds.
The results demonstrated that the co-product had higher protein content than the whole cells but had lower digestibility than whole cells. The co-product showed the highest digestibility for lysine, an essential amino acid that is often deficient in terrestrial crop-based aquafeed ingredients, as well as the highest eicosapentaenoic acid (EPA) digestibility.
The team also evaluated several diets with varying percentages of co-product replacing fishmeal. When 33 percent of fishmeal was replaced with the co-product, the Nile tilapia had fish growth and a feed conversion ratio and survival rate similar to those on the reference diet where fishmeal was seven percent of the diet. The team hypothesizes that the co-product may need to be enhanced with enzyme(s) to maximize nutrient availability and counter the lower digestibility observed in the experiment.
"The possibilities for developing a sustainable approach to aquaculture are exciting. Our society has an opportunity to shift aquafeed's reliance on fish-based ingredients to a fish-free product that is based on marine microalgae, and our findings provide new insight into how we can get there," says lead author, Pallab Sarker, research assistant professor at Dartmouth.
The research builds on the team's earlier work developing a marine microalgal feed for Nile tilapia made from Schizochytrium sp., which evaluated how the feed affected digestibility and growth. The results demonstrated that Schizochytrium sp. was highly digestible lipid and DHA, an omega 3 fatty acid source for tilapia. The tilapia not only had higher weight gain but better feed conversion compared to those on a control diet containing fish oil, when the Schizochytrium sp. fully replaced the fish oil.
As part of the team's goal to eliminate aquafeed's reliance on marine fish and terrestrial crop inputs, they are combining the Nannochloropsis co-product with other marine microalgae to make aquaculture feeds more sustainable.
Towards sustainable aquafeeds: Evaluating substitution of fishmeal with lipid-extracted microalgal co-product (Nannochloropsis oculata) in diets of juvenile Nile tilapia (Oreochromis niloticus). Pallab K. Sarker , Anne R. Kapuscinski, Ashley Y. Bae, Emily Donaldson, Alexander J. Sitek, Devin S. Fitzgerald, Oliver F. Edelson. PLoS ONE 13(7): e0201315.
Nile tilapia (Oreochromis niloticus) show high digestibility of lipid and fatty acids from marine Schizochytrium sp. and of protein and essential amino acids from freshwater Spirulina sp. feed ingredients. Sarker PK, Gamble MM, Kelson S, Kapuscinski AR. Aquaculture Nutrition (2016) 22(1): 109–119. https://doi.org/10.1111/anu.12230
Towards sustainable aquafeeds: complete substitution of fish oil with marine microalga Schizochytrium sp. improves growth and fatty acid deposition in juvenile Nile tilapia (Oreochromis niloticus). Sarker PK, Kapuscinski AR, Lanois AJ, Livesey ED, Bernhard KP, Coley ML. PLoS ONE (2016)11 (6): e0156684. https://doi.org/10.1371/journal.pone.0156684