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Can fish sludge feed the insects that can feed fish?

Black soldier fly larvae and marine worms have been raised on fish sludge with good results. Photo: SINTEF Ocean.
Black soldier fly larvae and marine worms have been raised on fish sludge with good results. Photo: SINTEF Ocean.

Researchers in Norway have been granted NOK 10 million (£832,000) to look at the possibilities of safely using fish farm sludge as a feed for animals such as black soldier fly, which could then be used to make protein for fish feed.

Sludge comprises faeces from the fish and uneaten feed and contains valuable nutrients.

Today, any sludge collected largely comes from on-land farms and goes to biogas and fertiliser production, and it costs fish farmers money to process and dry the sludge and to transport it for further utilisation. But experiments with the use of sludge as a substrate (feed) for organisms such as black fly larvae and marine worms have shown good results.

The SecureFeed project will investigate the need for and document measures that make such use biosafe, i.e., that there is no risk of spreading infection or toxic compounds.

Øyvind Hilmarsen: Using sludge as feed would be
Øyvind Hilmarsen: Using sludge as feed would be "circularly economically correct". Photo: SINTEF Ocean.

Biosafety

Project manager Øyvind Hilmarsen of SINTEF Ocean told Fish Farming Expert’s Norwegian sister site, Kyst.no: “It will be exciting to investigate whether fish manure can be used as feed raw material in a biosafe way. Such a use of sludge will be circularly economically correct, make salmon production more sustainable and increase the value of the sludge for fish farmers.”

Hilmarsen said that currently the law doesn’t allow sludge to be used as feed for animals, but if that changed then the value of sludge and the sustainability of the seafood industry would both increase.

200,000-tonne resource

He added that around 200,000 tonnes (dry weight) of sludge are currently discharged from Norwegian fish salmon, including from net pens.

“Resources that are wasted today can be part of new value creation,” Hilmarsen said.

SINTEF Ocean, the Institute of Marine Research and the Norwegian Veterinary Institute have been granted NOK 10m by the Norwegian Seafood Research Fund (FHF) for the SecureFeed project.

Black soldier fly larvae could be fed on fish sludge if it's found to be safe.
Black soldier fly larvae could be fed on fish sludge if it's found to be safe.

Knowledge collection

A systematic collection of knowledge will be carried out first, led by senior researcher Aksel Bernhoft at the Veterinary Institute. The goal is to make existing knowledge more accessible and usable, identify knowledge gaps, and help the project choose the right priorities. Among other things, better knowledge is required of the content of heavy metals and various relevant infectious substances in wet and dry sludge from salmon production.

“Then a number of experiments will be carried out with fish manure as feed for marine worms and black soldier fly larva, to detect the risk that the contaminants will be included throughout the process and transferred to the feed ingredients,” said Erik-Jan Lock, research manager at the Institute of Marine Research.

Arne Holst-Jensen, section leader at the Veterinary Institute, said: “There is consequently a need to document whether such utilisation is safe for the organisms from an animal welfare perspective, and that the end product is safe. This applies to both heavy metals and various relevant infectious substances.”

A working meeting will be held before the summer, for equipment suppliers for collecting, treating and drying sludge, as well as possible users of feed ingredients produced by insects and marine organisms fed on sludge.