Methane and carbon dioxide released as organic waste breaks down could help feed farmed fish, according to researchers at the University of Queensland in Brisbane. Their process uses those gases to grow protein-rich cells that may replace some of the fishmeal used in aquaculture.
Fishmeal is made from wild-caught fish, including small species such as anchovies. Its use can add pressure to ocean populations and requires long supply chains that produce greenhouse gas emissions. That challenge is growing as fish farming expands: farmed seafood is estimated to make up about 62% of all seafood produced worldwide by 2030.
The team, working at UQ's Biosustainability Hub, starts with gases produced when microorganisms break down organic waste without oxygen. This process is called anaerobic digestion. Researchers then use the carbon dioxide and methane to grow protein-rich cells. Once harvested and processed, those cells become an ingredient known as single-cell protein.
Dr. Lars Puiman, of UQ's Australian Institute for Bioengineering and Nanotechnology, said the ingredient has properties similar to fishmeal and could serve as a sustainable substitute. It is intended as a nutritious supplement for fish feed, not a finished feed product already in use. The technology remains under development, and the researchers plan to test it at pilot scale before trying it in aquaculture feeds.
The potential is meaningful even if fishmeal is not removed altogether. Puiman said studies have shown microbial single-cell proteins can replace up to 75% of fishmeal in barramundi diets. Barramundi is an important part of Australia's aquaculture industry, making it a useful species for exploring how much of the conventional ingredient can be swapped out.
The researchers have secured a patent for the biogas conversion process. Dr. James Heffernan, also of UQ's Australian Institute for Bioengineering and Nanotechnology, said the approach reuses carbon from organic waste to produce fish feed, while helping limit the need for additional emissions. He said gases generated by agricultural waste could also be converted, linking the technology to another major part of Australia's economy.
The team sees uses beyond fish feed, too. Heffernan said the process could be expanded to make alternatives for other animal feeds and soil fertilizers. For now, the next test is whether the protein can be made at pilot scale and perform well in aquaculture feed. Puiman said replacing fishmeal entirely is a long-term goal. The researchers are working toward a cost-effective product that can help fish farms grow while easing demand for wild fish.