Photo: Peter Vilhelm Skov

Fish can be fed plant waste products

Friday 15 Mar 19


Peter Vilhelm Skov
Associate Professor
DTU Aqua
+45 35 88 32 63


The global production of fish from aquaculture was 80 million tonnes in 2016.

Around 580 species are farmed in aquaculture plants around the world.

Fish has an excellent nutrition profile. They are a good source of protein, fatty acids, vitamins, minerals, and essential micronutrients.

Seaweed is accounting for an increasing share of global aquaculture production.

Turtles, frogs, edible jellyfish, sea cucumbers, and sea urchins are among the species being farmed in aquaculture. In Denmark, trout is the most commonly used species in aquaculture.

SOURCE: The UN Food and Agriculture Organization (FAO).


Danida is the term used for Denmark’s development cooperation, which is an area of activity under the Ministry of Foreign Affairs of Denmark.

Learn more on Ministry of Foreign Affairs of Denmark’s website. 

Fish from fish farms are feeding more and more mouths. But what should the fish eat? Research shows that plant proteins may be the answer.

Global demand for edible fish has been strongly rising for decades, according to the UN Food and Agriculture Organization (FAO).This is because the earth’s population is steadily growing, and the average person’s consumption of fish has also risen markedly.

Given that many of the world’s wild fish stocks cannot be exploited further, an increasing proportion of the global demand for fish, mussels, and prawns is being met by aquaculture—i.e. fish farming in sea cages or land-based pools.

In 2000, a quarter of the world’s food fish, prawns, and mussels came from aquaculture. In 2016, the latest figures from FAO show that this share had almost doubled to 46.8 per cent.

The rising aquaculture production increases the need for high-protein fish feed. The traditional feed solution has been based on fish meal, derived from industrial fish or fish waste products from the industrial processing of fish—tails, heads, bones etc.—ground into meal.

This raw material has to be imported in most parts in the world, and this can be an expensive solution for third world countries. Another problem is that the quality is not always good enough, reports Peter Vilhelm Skov, Associate Professor at DTU Aqua:

“It’s important that the protein composition is correct, otherwise the fish cannot exploit it optimally. Poor quality feed means poorer results from aquaculture, and ultimately lower food production.” 

Utilizing local resources

The associate professor has been working with researchers in Ghana on a Danida-funded project for the past four years. The aim was to find alternative feed solutions based on local ingredients. 

“Almost half of Ghana’s need for edible fish is being met by aquaculture, and demand for fish looks set to rise. So there is much to be gained if Ghana can get more out of their aquaculture production. There is also the potential to increase profits by using local ingredients for feed and thereby reducing the costs of imported feed,” says Peter Vilhelm Skov, who has supervised a number of Ghanaian PhD students who have travelled to DTU Aqua’s facilities in Hirtshals to do research in the project.

The researchers focused on side flows from Ghana's production of vegetable oils from local coconuts, peanuts, oil palms, shea nuts, cotton seed, etc. They investigated whether waste products from this oil production could be recycled as fish feed.

“The idea is not new. But Ghanaians have not had the opportunity to properly investigate the quality of the feed. We have been able to help with this in Hirtshals,” says Peter Vilhelm Skov.

Photo: Kwasi Adu Obirikorang
Danish and Ghanaian researchers are working together to develop alternative feed for fish farms. Fish farming can help relieve the pressure on wild fish stocks in a hungry world. Photo: Kwasi Adu Obirikorang.

Plant waste products replace fish meal

Before the researchers could start on feed trials, they had to get a picture of the volumes of side flows in Ghana’s vegetable oil production. They also had to consider the fact that some of the waste products are already being used for chicken feed etc., to avoid finding a fish feed solution that simply created a new problem in another sector. Only then could they start trials where fish were fed the alternative vegetable products, and examine the quality of these feed solutions.

The research trials focused on a number parameters, such as measurement of nutrients and oxygen in the water, nutrients in the fish faeces, and the fatty acid levels in the fish—which are an indicator of whether the fish will make a nutritious meal for humans.

“Feed quality can be measured in several ways. The primary one is fish growth. If the protein has the correct amino acid balance, the fish growth will be optimal. But we also look at how much of the feed the fish utilize, and how any unutilized residue affects the aquatic environment,” says Peter Vilhelm Skov, who also does research into how the environmental impacts from aquaculture can be reduced.

The researchers have worked out which waste products are the best vegetable alternatives to fish food in Ghana:

“We have shown that side flows from oil palms and peanuts can successfully replace fish meal in the feed, and this is a solution they are now starting to use in Ghana,” says Peter Vilhelm Skov, noting that the results are of interest to other countries also:

“There are many countries in the Equatorial belt that can exploit these vegetable alternatives to fish feed, because like Ghana, they also produce vegetable oils based on similar produce.”

Photo: Kwasi Adu Obirikorang   

Fish in aquaculture facilities in Ghana can be fed using waste products from local vegetable oil production.

Photo: Kwasi Adu Obirikorang.

Fish for a hungry world

According to the FAO, aquaculture is the food industry sector seeing the strongest growth. The growth is highest in Africa and Asia, with especially China standing out. China’s fish consumption is primarily based on aquaculture, with approx. 75 per cent of total Chinese fish production coming from fish farms in 2016.

Aquaculture is here to stay, also in Denmark.

Brian Thomsen is Director of Danish Aquaculture, which works to promote sustainable production and raise awareness of the value of the aquaculture industry to society. He believes that aquaculture can make a significant contribution towards feeding a hungry world:

“Aquaculture helps relieve the pressure on the wild fish stocks. Fish farming is environmentally friendly and resource-efficient animal production with high feed utilization and a low carbon footprint. This is in part because fish expend less energy on ‘maintenance’, because they are cold-blooded animals and live in water,” says Brian Thomsen.

Brian Thomsen also notes that countries like Denmark can serve as a role model for the rest of the world:

“In Denmark, we work hard to ensure that aquaculture does not impact on the surrounding environment, and the environmental aspects of our plants are continuously monitored. Denmark cannot supply the whole world with fish from aquaculture, but we can show the way to the sustainable production of healthy aquaculture products.”

Fish in aquaculture facilities in Ghana can be fed using waste products from local vegetable oil production.

Danish and Ghanaian researchers are working together to develop alternative feed for fish farms.

Fish farming can help relieve the pressure on wild fish stocks in a hungry world.


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