Renewable resources and their efficient utilisation are key to make aquaculture production as sustainable and profitable as possible. The UrbanAqua project conceptualises a circular economy in which residual materials and by-products are utilised directly and nutrients are upcycled within the loop. Three raw materials were identified for excellent residue and nutrient conversion: Duckweed (Lemna minor), insects (larvae of Hermetia illucens and legs of Acheta domesticus) and the cyanobacterium spirulina (Arthrospira platensis), all of which are also suitable and promising candidates for use in aquafeeds (Eide et al., 2024, Soma et al., 2024, Michini and Michael, 2024). While recent research clearly shows use of plant-based products in the fish feeds can lead to a reduction in growth performance due to antinutritional factors, these negative effects can be minimized to a negligible level through carefully designed ingredient combinations (Turchini et al., 2019).
Such hollistic feed approaches can provide a sustainable and regionally producible feed solution for land-based aquaculture and create new value chains. These developments align with emerging approaches that integrate microbially driven nutrient recycling with engineered systems converting agricultural waste streams into value-added biomass (Glockow et al., 2024).
The research work carried out here not only demonstrates the potential of the simple combination of the above-mentioned feed raw materials compared to a commercial formulation, but also provides insights into the effects of the respective sustainable feed raw materials duckweed, insects and spirulina on growth performance, metabolic and morphologic parameters. A total of six different diets were designed. A control diet was formulated to reflect a standard commercial composition. Diet 2 was designed following the commercial control; however, the test ingredients were incorporated as the principal raw materials, while fishmeal and fish oil remained included. Diet 3 was formulated entirely without fishmeal and fish oil, substituting these components with alternative sustainable ingredient sources. Diets 4–6 represented experimental formulations in which the test ingredients were incorporated at increasing inclusion levels (table 1).
Research Finding
Preliminary results of the 60-day trial show that the weight gain of fish that received the sustainable feed ingredients from circular economy was significantly increased compared to the conventional formulation (p<0.002). The increased use of insect meal led to compensation of growth depression caused by the omission of fish meal and fish oil in the sustainable test diets. The analysis of plasma levels of glucose, triglycerides, cholesterol, and total protein supports the findings from the growth parameters, allowing for the creation of a detailed overall picture. The feed formulation using duckweed, insect meal, and spirulina as a replacement — with minimal inclusion of fishmeal and fish oil showed optimal blood parameters, liver values, and growth. These results were similar for the feed that was free of fish meal and fish oil and an above-average amount of insect meal. The only difference observed was a slight increase in blood lipid levels, indicating potential for further optimization of the feed, although growth rates were high (SGR=2.3 % bodyweight day-1).
The study shows the suitability of different by-products that have arisen from residue streams from the recirculation of different species. However, further optimisation steps are necessary with regard to the formulation. Sustainability aspects such as nutrient recovery and by-product inclusion can be used to pioneer production of fresh fish products in urban areas.
Table
Table 1. Summary of experimental diets
Diet
Description
Fish meal and oil
Sustainable alternative oils
Commercial Control
Commercial formulation
Test Control
Closely after the commercial control; however, the test ingredients were incorporated as the principal raw materials.
Sustainable Control
Closely after the test control. Entirely without fishmeal and fish oil, with alternative and more sustainable ingredient sources
Increased Spirulina
Closely after the sustainable control but with increased amounts of Spirulina
Increased Insects
Closely after the sustainable control but with increased amounts of insect meal
Increase Waterlentils
Closely after the sustainable control but with increased amounts of waterlentils
Acknowledgment
The authors would like to thank all partners in the UrbanAqua project funded by the BaMS innovation cluster for their valueable inputs.
References
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Glockow, T., Kaster, A.-K., Rabe, K.S., Niemeyer, C. M. (2024) Sustainable agriculture: leveraging microorganisms for a circular economy. Applied Microbiology and Biotechnology Vol (108) https://doi.org/10.1007/s00253-024-13294-0
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