Copepods can disrupt marine fish farming

Luxury production is a showcase

Fishing has stagnated on a global level, and today, around 50% of the total fish production is from fish farms. At the same time, farmed fish is the fastest-growing source of protein in the food industry. In the context of a growing population, the industrial production of fish becomes a necessity.

“The demand for aquaculture farming is huge, and so is the commercial interest in it. Aquaculture, like the pork industry, is a knowledge-based industry. It takes a particularly great deal of research to streamline the industry and make it profitable,” Benni Winding Hansen points out.

Tuna is an obvious next step, as fresh tuna is an expensive and a popular delicacy and that puts a lot of pressure on the tuna stocks in nature.

Raising Yellowtail Kingfish in fish farms is a form of luxury production targeted towards the wealthier consumer segments who are ready to take up their chopsticks and have some sushi and sashimi. It is precisely the high kilo price of the fish that creates room for experimenting with hatching copepods as fish larvae food year-round.

“Yellowtail Kingfish raised in tanks are definitely not a cheap source of protein that can solve the world demand. We are instead testing a new concept on a high-value fish which, at length, can be introduced to the industry on a larger scale once the production methods are well-tested and the costs decrease,” Benni Winding Hansen states.

In the short run, the project is also demonstrating a large commercial potential for a more diverse production of marine fish species:

“We are currently raising relatively few species and the producers can sell as many high-value fish as they can make. Tuna is an obvious next step, as fresh tuna is expensive and a popular delicacy and that puts a lot of pressure on the tuna stocks in nature,” says Benni Winding Hansen.

From dormant eggs to an egg bank

When the production of algae in the boreal oceans decreases during the winter months due to the cold and dark, it is also the end for that years copepods. They lay so-called dormant eggs that drop to the bottom of the sea. It is only when spring arrives that the eggs are whirled up and hatched so that the waters once again become full of copepods.

The year-round production of copepods is based on this same cycle. In a laboratory, Benni Winding Hansen’s research group can simulate nature and they are now capable of storing dormant eggs from the copepod species Acartia tonsa in cool temperatures for a year - and, it should be mentioned, without the eggs losing the ability to hatch.

“For the fish farmers, this means that in the future they will have access to a backup system. If the production of copepods should suffer from disease, accidents or fail in some other way, they can extract material from an “egg bank” based on copepod eggs in cold storage. This makes it possible to produce copepod larvae year-round. This is the exact process that we will be completing on a large scale in the production of Yellowtail Kingfish in northern Jutland,” says Benni Winding Hansen.

Experiments with extending the season for micro-algae - a prerequisite for the farming of copepods - is also part of the production of Yellowtail Kingfish. This is done by covering the outdoor copepod tanks with greenhouses and using artificial lights so that the micro-algae can reproduce for a longer period of the year and ensure that the copepods have food.

If someone thinks that society doesn’t need nerdy basic research and can jump straight to the application phase, they are gravely mistaken.

Stress-free copepods

Over the last couple of years, the research group has succeeded in pushing the boundaries of how densely copepods can be grown. It is a critical issue for commercial production, where every cubic metre of water in the basin is an added expense.

“In order to increase the density, we need to measure the right things. In the beginning, we measured the mortality rate, but it takes a lot to kill a copepod. Instead, we need to measure how when they begin encountering physiological stresses and how long the copepods can reproduce. It’s all about getting some eggs produced. Lately, on the gene level, we have also studied how copepods in crowded cultures become stressed,” says Benni Winding Hansen.

Just as with humans, the oxygen consumption reveals the stress levels in copepods. On that basis, well-being can be measured by the copepods’ oxygen consumptions and patterns of movement, and this has given us new knowledge about how the stress proteins of an organism are activated.

“Previously, the assumption was that there could only be a few thousand copepods per litre of water. Now we have demonstrated that we can have 5,000 - 10,000 copepods per litre before the crowded conditions impact them. This is a huge win, that we can increase the density so much without it having a negative impact on the copepods’ ability to lay eggs,” Benni Winding Hansen explains.

“The entire basis for an innovation project such as this is that I’ve spent 15 years on the research behind it. I know the ecology and physiology of copepods inside and out. If someone thinks that society doesn’t need nerdy basic research and can jump straight to the application phase, they are gravely mistaken. It is precisely because I’ve done my own background research and made my discoveries that I can now implement them in managed aquaculture processes,” Benni Winding Hansen points out.

Published in Rubrik #15, 2019