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A freshwater fish that’s pure to the bone

A freshwater fish that’s pure to the bone

Bio-engineers from KU Leuven have premiered the most sustainable feeding and farming program for the omega perch ever developed.

6 minutes
02 June 2020

Bio-engineers from KU Leuven have premiered the most sustainable feeding and farming program for the omega perch ever developed. It’s vegetarian, full of healthy fats and environmentally friendly.

‘Haring in het land, dokter aan de kant.’ (‘A herring a day keeps the doctor away.’) It’s just one of the many sayings that indicate how healthy eating fish is. Fish is leaner than meat or dairy, contains lots of proteins and essential, unsaturated fatty acids. This, however, only applies if the fish does not contain antibiotics or microplastics. The enthusiastic consumption of fish also has harmful consequences such as overfishing, with wild fish being caught en masse, and pollution, with farmed fish raised in cages and polluting sea or river water.

With an eye toward a more sustainable, healthy future, KU Leuven started a research program in 2009 aimed at developing a fish species that counteracts these harmful phenomena and can be bred for human consumption. A freshwater fish that’s pure to the bone: healthy, tasty, local and ecological.

The search led two KU Leuven biologists, Dr. Ivo Roelants, working at Leuven Research & Development, and Bruno Goddeeris, a biology professor and veterinarian in the Biosystems Department of the KU Leuven Faculty of Bio-Engineering Sciences, to the Billabong, a wetlands area in the north of Australia. There lives the jade perch, a robust species that thrives in both a freshwater and a brackish environment. It grows fast and requires little space, water or food. One kilo of fish can be produced using only 50 litres of water. For comparison: 250 litres are needed for other farmed fish, and 7000 litres for a kilo of beef. Moreover, 700 grams of food is enough to raise 500 grams of jade perch.

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After importing and sampling different fish, Goddeeris and Roelants decided they had the right fish on the hook. But how could they raise it at KU Leuven? Nobody was using aquaculture to breed the jade perch at that time, but it’s an essential link in this sustainability story. A water and energy-efficient system was chosen that can keep recirculating water clean and germ-free: the Recirculating Aquaculture System.

Thanks to research capital from the province of Flemish Brabant, all that was needed was to find the right researcher.

A plate full of omega-3 fatty acids

Stijn Van Hoestenberghe seems to be the right man for the job. As a child he was fascinated by goldfish, as a diver he’s inspired by the fragile beauty of the ocean, and as a biologist he’s passionate about sustainable fish farming. He’s previously bred sea bass in Spain and prawns in the Seychelles, and is now returning to his alma mater to start a doctorate on the jade perch.

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He’ll begin as soon as he’s installed the fish tanks, including their four-meter high filters, utilising the help of KU Leuven technical staff to get everything set up in the old Institute for Bacteriology. He’s renamed the jade perch the omega perch in a nod to its high omega-3 fatty acid content, which is even higher than in salmon or mackerel. Our body needs these unsaturated fatty acids, but cannot make them itself and so has to get them from our food. In practice, many people don’t get enough because their diet is too limited. The omega perch can help them immediately.

Moreover, it is by all indications – and perhaps most importantly – a very tasty fish, somewhat like sea bass or golden bream. You can prepare it traditionally, breaded or baked, but thanks to its firm structure and nutty taste, it’s also suitable for sushi, tartar or carpaccio. Its high fat content makes it ideal for smoking, while its lack of bones and mild taste can tempt even the pickiest children. Jeroen Meus, too, immediately tacks and speaks of ‘a surprising fish full of character and numerous culinary possibilities’.

100% vegetarian

Meus can cook with confidence, because the Leuven omega perch is raised in a closed system of pure rainwater, free from antibiotics and microplastics. Moreover, the lab where Van Hoestenberghe works has developed a completely plant-based diet and in doing so created a world first: only Belgium has vegetarian farmed fish. Farmed salmon, cod, sole or sea bass usually receive pellets of fishmeal and fish oil, which means that other smaller wild species still have to be caught; a kilo of farmed salmon, for example, requires three kilos of wild fish – harmful to fish stocks, biodiversity and other predators such as penguins.

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After years of study, Van Hoestenberghe has come up with a unique mix of locally grown seeds and grains that offers the right mix of proteins, fats and sugars. Because the omega perch doesn’t behave territorially, more than 100 kilos can be produced in one cubic metre of water. It also appears to be resistant to diseases.

Awareness of this ‘most sustainable fish in the world’ is spreading like wildfire and Van Hoestenberghe wants as many consumers as possible to enjoy it. Aqua4C, a spin-off of KU Leuven, is on board. In 2014, the then-Minister of Agriculture and Environment, Joke Schauvliege, laid its corner stone in Kruishoutem. Today, they raise 100 tons of omega perch per year, around 200,000 units in total. Current customers include not only Carrefour, Spar and Albert Heijn, but also starred restaurants in Flanders and Wallonia.

The fish of the future

Aqua4C, which still receives support from KU Leuven, has gone one step further in its innovative breeding process by being the first aquaculture company to join forces with a horticultural colleague, its close neighbour Tomato Masters. A real synergy is thus created, a model of agricultural integration.

The tomato greenhouses collect rainwater, and up to 30,000 litres of that water are used each year to fill the 27 large concrete fish basins. That water is maintained at the ideal growing temperature of 27 degrees thanks to green energy produced from the heat of the greenhouses. Conversely, after filtering and purification, the wastewater from the basins appears to be a rich natural source of essential plant nutrients such as nitrogen, phosphorus, potassium, calcium, iron and magnesium. They make the tomatoes grow better, which means that Tomato Masters needs to add fewer nutrients. It is a fully circular subsystem.

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Bio-engineer Charles-Aimé Fransman, also a doctoral student under Goddeeris, is currently finalising a study on local production of omega perch. This will ensure that Aqua4C can control the entire process and therefore guarantee the health, purity and sustainability of its fish. After all, with the company no longer dependent on imported fish, it no longer needs to fight against the associated risk of disease.

The Leuven researchers firmly believe that the omega perch is the fish of the future. It has a minimal ecological footprint thanks to its plant-based diet and therefore doesn’t prey on fish stocks in the open ocean, it can easily be farmed locally and consequently causes less transportation pollution, it prevents overfishing, and it reduces the need for intensive mass fish farming that can be harmful to nature. It is also free from metals, antibiotics and microplastics, and makes it possible to reduce water use in food production.

‘It’s thought that we’ll need to double the current amount of farmed fish globally by 2040 in order to meet rising demand. So we need to fundamentally rethink how we farm fish.’ says Van Hoestenberghe. ‘We believe that we hold the key to real change, and that matches our stated ambition.’

Soon the old adage may sound a little different: ‘An omega perch a day keeps the doctor and the pollution away.’