Farmed fish on the menu—how to ensure sustainable seafood

Bacteria break down discharges

In land-based facilities, salmon swim in water that is continuously treated through an advanced filtration process, allowing the water to be reused. Only a small proportion of the water is discharged into the surrounding aquatic environment and replaced with new water. This means that the fish can be farmed with very low water consumption and minimal environmental discharge. 

Mechanical filters remove nutrients from the system, while bacteria convert the harmful ammonia in the water into less toxic nitrate during the final stage of the treatment process. 

In a research project, DTU scientists have developed a solution that optimizes the bacterial process by creating improved conditions for the bacteria that break down waste products. This is achieved by carefully adjusting a number of factors such as oxygen level, pH, and water temperature. 

Although nitrate is less toxic, it still needs to be removed. This is done through end-of-pipe denitrification, where bacteria convert nitrate into harmless nitrogen gas. If not properly managed, however, the process can produce nitrous oxide instead.

“Nitrous oxide is a greenhouse gas that is up to 300 times more potent than CO2. With this project, we provide fish farmers with tools to finetune their discharge and nutrient removal processes, not only improving water quality, but also reducing greenhouse gas emissions from the farms,” says Carlos Octavio Letelier-Gordo, Senior Researcher at DTU Aqua and one of the scientists behind the project.

Improvements increase production

In addition to the reduction of greenhouse gases, the optimization also means that fish farmers can produce more fish. Previously, Danish aquaculture was regulated based on how many fish a facility was allowed to produce, which limited the production—regardless of how efficient or environmentally friendly the operations were. This changed with the introduction of the Food and Agriculture Package in 2015. Today, aquaculture is instead regulated based on the amounts of nutrients, particularly nitrogen and phosphorus, that a facility is permitted to discharge.

“We’ve succeeded in reducing discharges by more than 85 percent. With such a significant reduction, fish farmers can produce many more fish within the same facility,” says Carlos Octavio Letelier-Gordo.

This bacterial optimization is expected to increase the production capacity of the farms by up to 50 percent.

Intelligent monitoring

To ensure that the sludge-degrading bacteria operate as efficiently as possible, monitoring by staff with expertise in water quality and the underlying systems is required - making the process costly and time-consuming for fish farmers. 

Researchers from DTU Aqua are exploring the possibility of automating the treatment process using artificial intelligence (AI). The goal is for AI to determine when different treatment mechanisms are needed to maintain optimal water quality.

“We’re trying to eliminate the need for human involvement in the technical complexity and let AI take over control, so fish farmers can focus on the fish — and not on pumps, sensors, and bacteria,” says Carlos Octavio Letelier-Gordo.

According to the senior researcher, tests conducted at several industry facilities have shown promising results. However, there is still progress to be made before AI can fully manage land-based aquaculture systems.

Focus on fish welfare

The fish swim in large numbers within aquaculture facilities, making it difficult to assess their well-being accurately.

“When we think of animal welfare, we often picture chickens or pigs in overcrowded conditions. But for fish, that may not be the most critical aspect. Water quality plays a major role in their welfare and poor conditions can cause stress.” says Per Bovbjerg.

Today, stress in fish is assessed through indicators such as meat quality and through fish behaviour in the water. According to the Danish Animal Welfare Act, animals must be treated properly and protected as much as possible from pain, suffering, anxiety, and lasting harm. However, there is no clear framework for how these requirements are upheld in fish farming. 

As part of a large-scale EU project focused on animal welfare, Manuel Gesto Rodriguez, Senior Researcher at DTU Aqua, is working to identify risk factors that threaten fish welfare in aquaculture. Through this work, he aims to develop clear guidelines to help fish farmers to maintain good fish welfare.

“The current regulation does not provide any details on how the fish should be farmed. I have no reason to believe that the fish are not okay in the facilities, because that would also be bad business for the farmers. But the honest answer is that we simply don’t know, because no one is systematically monitoring the fish,” says Manuel Gesto Rodriguez.

He expects that an EU project will lead to specific requirements for fish farming, which he sees as a positive step towards greater emphasis on fish welfare.