Bristle worms and insects are natural food for fish and animals, and some species are already approved for use in feed for animals such as salmon, pigs and chickens. In nature, insects and bristle worms feed on dead organic material. At the same time, increased circularity must not come at the expense of food safety and animal health.
“There are strict rules governing what insects and bristle worms are allowed to eat. The regulations are based on the precautionary principle. Increased knowledge may make it possible to use more side streams in the production of insects, which in turn can be used for fish or animal feed,” explains Senior researcher Inger Beate Standal.
“Insects and bristle worms are subject to the same strict feed regulations as other forms of animal husbandry. When these rules were developed, insect farming was not envisaged as a way of utilising waste resources or producing nutrient-rich biomass,” she adds.
The regulations set clear limitations: Insects may only be fed plant-based products, as well as a few animal products, such as fishmeal.
In the dFUSE project, researchers have investigated whether salmon that die before normal slaughter can be used as feed for insects and bristle worms.
Can we utilise more of the resources?
Norway is the world’s largest producer of farmed salmon, but not all fish end up as food. There can be many reasons why salmon die before slaughter. This may be due to disease, handling and delousing processes, but also causes such as technical or human failure. Environmental impacts, such as jellyfish or algae, can also play a role.
Fish that die in the cage or in well boats can generally not be used as feed. They are ensiled, meaning they are ground up and treated with acid and heat to kill microorganisms and ensure stable quality. Today, silage from so-called dead fish goes to biogas production, incineration or fertilisers. In just a few hours, the fish has gone from being food, to becoming a low-value side stream.
Even with a target of five per cent mortality, this represents large volumes. It also means that valuable marine proteins and fish oil in many cases are not utilised for feed or food.
“In the dFUSE project, we have looked at which causes of death result in the largest volumes, and whether the risk of disease transmission when using these as feed for insects and bristle worms is manageable. Examples include fish that die from injuries, or fish that die with wounds. We have also examined whether infectious agents or other undesirable substances can be passed on in the feed chain,” says Standal.
Fish with a high risk of infection, such as fish carrying hardy viruses, were not considered, as this type of raw material can and should be avoided anyway.
Tracking bacteria
In the experiments with infectious agents, various bacteria were added to the feed for insects and bristle worms. The researchers investigated whether the bacteria survived processing (acid and heat) and feeding to insects/bristle worms.
Bacteria on fish are adapted to life in the sea, and some were difficult to keep alive until the experiments started. Therefore, more resilient bacteria were also used, to see whether these survived processing and cultivation. The results from processing with acid and heat (ensiling) showed that the bacteria did not survive as long as the temperature was high enough throughout the entire fish biomass.
In the experiments with insects and bristle worms, the researchers analysed DNA, which provides an overview of the total bacterial content. They also analysed RNA, which gives better information on whether the bacteria are alive and active.
“The results showed that the bristle worms had ingested the bacteria. We found bacterial DNA both in the bristle worms and in the faeces, but there were no traces of living test microbes in the bristle worms,” says Standal.
“The experiments with insects showed the same. Even though we could detect the test bacteria that had been added to the feed, we were unable to detect these in the insects themselves. At the same time, it is important to ensure that any infectious agents in feed residues or faeces are not passed on in the feed chain.”
The project has shown that the ensiling process effectively kills infectious agents that may be present in the raw material. The feeding trials with insects and bristle worms further show that even though they consumed the test bacteria, these were not found in the organisms themselves. This means that the bacteria are either not taken up, or they are broken down.
Infectious agents may nevertheless be present in feed residues and be excreted in faeces. It will be important to remove such residues when producing feed. In addition, insects and bristle worms must be heat-treated before they can be used in fish feed. This heat treatment will also help reduce the risk of infection.
Low risk
“Overall, the results suggest that the risk of infection is very small when we ensile the raw material, use it as feed for insects and bristle worms, and heat-treat the biomass before it is included in fish feed,” concludes Standal.
“A more current issue is the possible presence of salmon protein residues in the biomass if the insects are to be used in salmon feed,” she says.
The salmon proteins must either be removed or broken down into smaller components before they can be used in feed for salmon, in line with the species barrier. This is a regulation that was introduced in the wake of the BSE outbreak in the early 1980s. However, it is worth noting that such disease has not been detected in fish so far.
The dFUSE project has thus contributed documentation indicating that parts of the resources from fish that die before slaughter, after appropriate treatment, can be used to farm insects and bristle worms. This biomass can in turn be included as an ingredient in fish feed. A true example of the circle of life.
Project information
The dFUSE project, “Improved resource utilisation and increased value creation from fish that die in cages”, is a collaborative project between SINTEF Ocean, the Norwegian Veterinary Institute, the Institute of Marine Research, Aquacloud and Pelagia. The project is financed by the Norwegian Seafood Research Fund (FHF #901914). The main objective of the project is to develop new methods, products and documentation that can make it possible to bring a larger share of this resource into a feed chain.
