Seaweed and maggots as feed for farmed fish: are there microbiological risks for human consumers?

Blog post by Isobel Swinscoe

If you were to be asked ‘What do farmed fish in Europe eat?’, your first answer would probably not be insect larvae! And you’d be right. Concerns about overfishing wild catch to feed farmed fish has led to greater inclusion of vegetable ingredients in aquafeed, leading to competition with human food resources. Yet providing an insect diet is established and accepted practice in fish farms throughout Africa, Asia and South America. Insects form part of the natural diet of almost all species of farmed fish, and have proven to be as equally nutritionally valuable to fish as commercial feed.

Europe has finally been given the green light to at least partly replace commercial fish feed with sustainable insect sources of protein from July 2017. Yet the insects are currently considered ‘farmed animals’ and therefore have to be reared on expensive commercial feed. Insects of many species are the ultimate natural convertors of organic waste into protein- and lipid-rich larvae. However, animal manure or catered food waste as insect feed, often used in the developing world, pose a risk of introducing dangerous bacteria to the insects, the fish and, eventually, human consumers.

So what could the insects be fed instead? The Aquafly project, led by the National Institute of Nutrition and Seafood Research, Norway, had a brilliant idea…. how about seaweed?! It’s an abundant organic material which would provide a source of Omega-3 for the insects, the fish and, ultimately, human consumers.

Then there was the choice of insects. A tropical, terrestrial species called Black Soldier Fly was an obvious choice as it’s already reared on an industrial scale in Europe for livestock and pet feed, the larvae contain very high protein and fat levels, and the adult fly does not transmit disease to humans.

A University of Stirling PhD, my role in the Aquafly project is to evaluate the risk of environmental bacteria, which may prove dangerous to human consumers, entering this highly novel feed and food chain. Essentially, how safe are your salmon fillets if they’ve been fed fly larvae which have been wholly or partly reared on seaweed?

Several big commercial and research partners got on board with this project. Ocean Harvest in Ireland was responsible for providing powdered seaweed. Protix Biosystems in the Netherlands reared the Black Soldier Fly larvae partly on the seaweed supplement. EWOS Innovation in Norway produced fish feed pellets using the larvae meal. Finally, GIFAS in Norway will undertake the feeding trials using sustainably farmed Atlantic salmon this year.

Since last year, I’ve been lucky enough to visit the first three of these companies, and see the inner workings of innovative animal feed production, as I followed the seaweed powder and larvae products throughout the industrial processing chain. The general public rarely get to experience the cutting edge of research and industry working together! My microbiological screening of the freshly harvested seaweed, and raw ingredients fed to the larvae, through to the fish feed pellets showed that seaweed is an entirely microbiologically safe feed ingredient for insect larvae. It was also clear that feed pellets produced using Black Soldier Fly larvae as a protein source were free of any bacteria dangerous to humans. A great result for Aquafly!

The final stage of the project is now fast approaching… the Atlantic salmon feed trials in northern Norway. Will the salmon fillets be safe for consumers to eat? Check back here soon for the next exciting instalment…

The long-term environmentally and economically sustainable production of Atlantic salmon is essential to both Scotland and Norway’s economies. This PhD research project is Match-funded by the University of Stirling and the National Institute of Nutrition and Seafood Research, Norway.

To find out more about the Aquafly project, follow the link:

Update: read Isobel’s publication: Seaweed-fed black soldier fly (Hermetia illucens) larvae as feed for salmon aquaculture: assessing the risks of pathogen transfer to find out more about her work with black soldier fly larvae and seaweed.