Towards sustainable aquafeeds: Evaluating substitution of fishmeal with lipid-extracted microalgal co-product (Nannochloropsis oculata) in diets of juvenile Nile tilapia (Oreochromis niloticus)

PLoS One. 2018 Jul 31;13(7):e0201315. doi: 10.1371/journal.pone.0201315. eCollection 2018.

Abstract

Microalgae companies increasingly seek markets for defatted biomass that is left over after extracting omega-3 rich oil for human nutraceuticals and crude oil for fuels. Such a protein-rich co-product is a promising alternative to unsustainably sourced fishmeal in aquaculture diets. We report the first evaluation of co-product of the marine microalga Nannochloropsis oculata (N. oculata co-product) for replacing fishmeal in diets of Nile tilapia, a globally important aquaculture species. We conducted a nutrient digestibility experiment with N. oculata dried whole cells and N. oculata co-product, followed by an 84-day nutritional feeding experiment with N. oculata co-product. N. oculata co-product, more nutrient-dense than whole cells, had the highest digestibility for lysine, an essential amino acid that is often deficient in terrestrial crop meals; and for 20:5 n-3 EPA, making it a good option for EPA supplementation in tilapia feed. N. oculata co-product, despite containing higher amounts of protein than whole cells, had significantly lower digestibility for crude protein than whole cells. Apparent digestibility coefficients (ADC) of methionine were significantly lower in N. oculata co-product than in whole cells. The nutritional feeding experiment compared diets with N. oculata co-product that replaced fishmeal as follows: 0% replacement in reference diet (fishmeal as 7% of total diet) and test diets with 33%, 66% and 100% replacement of fishmeal (3%, 5.5%, and 8% of total diet, respectively). Results showed the 33% replacement diet yielded fish growth, feed conversion, and survival similar to the reference diet. Reduced digestibility and growth at greater N. oculata co-product inclusion levels may have been due to higher levels of anti-nutrients in co-product than whole cells. All diets yielded a n3:n6 ratio of tilapia fillet that is favorable for human consumption. Depositions of macro minerals and several trace elements in the fillet were not significantly different across diets. Thus, N. oculata co-product, when replacing 33% of fishmeal in tilapia feed, led to fish performance and flesh composition comparable to that of fish fed the reference diet, but its nutrient digestibility needs to be improved to achieve higher replacement levels.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animal Feed*
  • Animals
  • Fisheries*
  • Microalgae / chemistry*
  • Stramenopiles / chemistry*
  • Tilapia / growth & development*

Grants and funding

This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2016-67015-24619 from the USDA NIFA (to Dr. Pallab K. Sarker); and the Sherman Fairchild Distinguished Professorship in Sustainability Science (to Dr. Anne R. Kapuscinski), Vranos Family Fund, and Dean of the Faculty of Arts and Sciences, Dartmouth College. We thank Qualitas Health, Inc. for donating Nannochloropsis oculata whole cells and co-product for this research, Alyssa Gao and Cameron Grimes for work on lectin assays, and Paul Zietz, Dartmouth Environmental Measurements Lab Manager, for conducting analytical chemistry. The funders contributed to this work, had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.