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

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.

Effects of three carbohydrate sources on water quality, water consumption, bacterial count, growth and muscle quality of Nile tilapia ( Oreochromis niloticus ) in a biofloc system

“…The high n‐3/n‐6 ratio of 2.8–3.39 obtained in the present study is due to the presence of higher proportion of DHA in the muscle tissues. This ratio is much higher than the n‐3/n‐6 ratio of 0.8–0.9 reported by Sarker et al (2018). Moreover, the high muscle n‐3/n‐6 ratios obtained in the present study compared to the recommended 1:1 ratio for optimal human health are a good indication of the nutritional and health status of tilapia raised in BFT.…”

“…(2014) for GIFT Nile tilapia fed diets containing different levels of perilla oils, but lower than the 5.4%–6.10% reported by Sarker et al (2018). However, the ∑SFA range of 49.59%–55.21% obtained in this study is higher than the 36.35%–36.7% found by Sarker et al (2018) in Nile tilapia fed diets containing a coproduct of marine algae ( Nannochloropsis oculata ). However, Sarker et al (2018) reported slightly higher ∑MUFA and ∑PUFA values in tilapia muscle than this study.…”

Mesopelagic Species and Their Potential Contribution to Food and Feed Security—A Case Study from Norway

“…Already, studies have shown that cetoleic acid, which is especially high in lantern fish species, stimulates the capacity of human and salmon cells to produce EPA and DHA, and enhance the retention of EPA and DHA in Atlantic salmon [72]. One key challenge for sustainable aquaculture development is sufficient feed ingredients that can produce healthy and robust fish [17,78,79]. Currently, Norwegian farmed salmon are fed more than 70% plant feed ingredients on average [80], with similar levels in Chile, Canada and Australia, while Scotland salmon diets contain slightly higher levels of marine feed ingredients [81].…”

The Future of Aquatic Protein: Implications for Protein Sources in Aquaculture Diets

“…77 The nutritional quality of microalgae is high, with a crude protein content of up to 71% and a lipid content of up to 40%, which are comparable with that of terrestrial plant and animal sources. [78][79][80] Microalgae have the potential to replace fish meal and fish oil in aquafeeds 71,77,81 and many studies have demonstrated the successful use of microalgal biomass as a feed additive or fish meal replacement for a range of aquaculture species, generally with positive effects on growth and quality 70,[81][82][83][84][85][86][87] ( Figure 3C). The biological capacity of microalgae, underpinned with positive research findings on the replacement efficacy in aquafeeds across many aquaculture species, suggests that there is high potential for the use of microalgae as a protein source.…”