Aquaculture relies on fish meal (an ingredient derived from wild fish) as the main protein source for feeds. This raises sustainability concerns. However, a new study offers a promising alternative: single-cell protein (SCP). Produced from soy processing wastewater, this innovative protein source could revolutionize fish feeding.
Scientists at Nanyang Technological University, Singapore (NTU Singapore), and Temasek Polytechnic have successfully replaced half of the fish meal protein in Asian sea bass (Lates calcarifer) diets with “single-cell protein” obtained from microbes cultured in soy processing wastewater, paving the way for more sustainable aquaculture.
Using a cultured protein is new in aquaculture production, say scientists from the Singapore Centre for Environmental Life Sciences Engineering (SCELSE), leading NTU’s efforts in the study, and the Aquaculture Innovation Centre (AIC) at Temasek Polytechnic.
The alternative: single-cell microbial protein
Single-cell protein, a sustainable alternative, can be cultivated from food processing wastewater. Particularly, soy processing wastewater contains organisms with probiotic potential that are essential for the healthy growth of fish.
Wastewater from the food processing industry is free from pathogens and other contaminants, making it suitable for microbe cultivation. Typically, after processing, wastewater is discharged and flows into a wastewater treatment plant. Its nutrients aren’t recovered, resulting in a missed opportunity to maximize resource use.
Researchers studied the use of SCP as a partial substitute for fish meal in juvenile Asian sea bass diets. They conducted a feeding trial with two groups: one was fed a control fish meal diet, and the other was fed a diet with 50% of fish meal replaced by SCP.
Harnessing microbial communities
Dr. Ezequiel Santillán, co-lead author of the study and principal investigator at SCELSE, said, “Our study represents a significant step forward in sustainable aquaculture practices. By harnessing microbial communities from soy processing wastewater, we have demonstrated the viability of producing single-cell protein as a viable alternative protein replacement in fish feeds, reducing reliance on fish meal and contributing to the sustainability of the aquaculture industry.”
The joint research team said their waste-to-resource conversion approach addresses food security and waste reduction, supporting the development of a circular economy with zero waste as described in the United Nations’ Paris Agreement.
The study is also aligned with AIC’s approach to improving food security and resilience. As the aquaculture industry aims to meet 30% of Singapore’s total nutritional needs by 2030, AIC has been actively advocating for intensive aquaculture production with innovation and technology.
Substituting fish meal
To demonstrate their approach, the team added soy processing wastewater from a food processing company in Singapore to bioreactors (a controlled environment for biological and chemical reactions) to culture single-cell proteins.
The laboratory-scale bioreactors operated in repeated cycles of controlled nutrients and low air supply (microaerobic conditions) for over four months at 30°C. These conditions suggest the team’s method can easily be replicated at room temperature in tropical regions like Singapore, further reducing the environmental footprint of fish meal production.
After producing their single-cell protein, the research team fed two groups of juvenile Asian sea bass for 24 days. One group received a conventional fish meal-based diet, while the other group received a diet containing half fish meal and half single-cell microbial protein. Both diets provided the same amount of nutritional content to the juvenile fish.
At the end of the experiment, the growth of both groups was assessed, and the researchers found that the fish had grown in the same amount. Interestingly, the group of fish with the new diet showed more consistent and less variable growth than the traditional diet group.
Single-cell protein accelerates growth
Professor Stefan Wuertz from NTU’s School of Civil and Environmental Engineering and Deputy Director of the SCELSE said, “The findings suggest that diets including single-cell protein may help fish grow more evenly, and it could be interesting to explore how this diet affects fish on a deeper level for future research.”
More importantly, the study has successfully demonstrated the potential to turn soy processing wastewater into a valuable resource for aquaculture feed, contributing to the transition to a “circular bioeconomy.”
Key results include:
- Similar growth: After 24 days, both groups of fish showed similar weight gain, feed conversion ratio (FCR), and specific growth rate (SGR). This indicates that SCP can effectively replace fish meal without compromising fish growth.
- Reduced variability: Interestingly, the group fed the SCP diet showed less variability in weight gain and FCR compared to the control group. This suggests a potential benefit for overall fish health and farm consistency.
- Champion of sustainability: The use of SCP not only reduces reliance on wild fish but also utilizes a waste product from soy processing. This creates a more sustainable and environmentally friendly approach to aquaculture.
Dr. Diana Chan, co-lead investigator of the study and director of the Aquaculture Innovation Centre (AIC), said, “The results of our fish feeding performance tests are promising for the aquaculture industry as they offer an alternative protein source to meet the growing need to replace fish meal, whose supply has become very costly and unsustainable.”
It is noteworthy that the microbial community in SCP was dominated by Acidipropionibacterium and Propioniciciclava, genera known for their potential probiotic properties and production of valuable metabolites. These additional benefits could further improve fish health and gut function.
Next steps
While lysine supplementation may be necessary to meet full protein requirements, this study highlights the immense potential of SCP as an effective and sustainable fish meal substitute. Further research can explore optimizing single-cell microbial protein production and its long-term effects on fish health and performance.
For their next steps, the research team will conduct tests over longer growth periods with higher levels of fish meal replacement. Researchers will also expand the study to include additional aquaculture species and different types of food processing wastewater.
On the other hand, various research groups are studying the potential of single-cell organisms (microalgae, yeasts, bacteria) as a protein source for aquaculture feed production.
The study was funded by the Singapore National Research Foundation (NRF) and Ministry of Education under the Research Centre of Excellence Program, and the NRF Competitive Research Programme “Recovery and microbial synthesis of high-value aquaculture feed additives from food-processing wastewater.”
Contact
Diana Chan Pek Sian
Aquaculture Innovation Centre, Temasek Polytechnic, Singapore, 529757, Singapore
Email: Diana_CHAN@tp.edu.sg
Stefan Wuertz
Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore, 637551, Singapore
Email: swuertz@ntu.edu.sg
Reference (open access)
Santillan, E., Yasumaru, F., Vethathirri, R. S., Thi, S. S., Hoon, H. Y., Sian, D. C., & Wuertz, S. (2024). Microbial community-based protein from soybean-processing wastewater as a sustainable alternative fish feed ingredient. Scientific Reports, 14(1), 1-11. https://doi.org/10.1038/s41598-024-51737-w
