Greenhouse gas emissions of rainbow trout fed from the Baltic region evaluated using Life Cycle Assessment

Recently, Mistra Food Futures released a report related to greenhouse gas emissions from rainbow trout farming. Researchers from RISE have compared the climate footprint of rainbow trout fed with conventional feed, based on e.g. fish meal, chicken and pig protein and soya, and new feed with raw materials from the Baltic Sea region such as insect protein, fish meal, sole, mussel, and vegetable proteins.

Global aquaculture production hit a new record in 2020, with a total production of over 120 million tonnes, contributing to almost half of the global consumption of seafood. Swedish aquaculture is currently small, but politicians, industry and research want to see sustainable growth, with a reduced environmental footprint. In intensive aquaculture where feed is used, feed often accounts for the largest part of the environmental impact, which means that feed development is a priority to increase sustainability.

The aim of the study was to compare the carbon footprint of rainbow trout reared on a more regional and circular feed with a high content of insects reared on residual streams, compared to a feed based on conventional feed materials such as soya and animal proteins from chicken and pig. The study calculated greenhouse gas emissions in a life cycle assessment (LCA) and shows that it is possible to produce a rainbow trout feed based on Nordic ingredients with a focus on circular and sustainable choices, while maintaining fish growth and with no apparent impact on fish health.

– The new feed reduces greenhouse gas emissions per kg of rainbow trout by more than half. “Fish fed the experimental feed had the same growth and economic feed conversion ratio (eFCR) as fish fed the control feed,” says Markus Langeland, who led the study. The reduction is mainly due to the significantly lower emissions from the experimental feed, estimated to be less than a third of the reference feed.  Circular use of residues is a fairly new area and there is still some uncertainty related to both the production of the new raw materials and the calculation method. The result is affected by, among other things, whether residual streams are considered as waste or by-products, and thus have a climate impact.

Feeding fish with insects reared on plant-based waste streams from the food industry increases circularity while reducing emissions. Replacing feed materials linked to land use change (e.g. deforestation), such as soy from South America (but also by-products of animals raised on soy), with climate-efficient and regionally produced feed materials led to large emission reductions. However, more local/regional is not by definition more sustainable, as each feed material is produced and transported differently, which determines its sustainability.

The analysis could not show any direct advantage in the use of regional raw materials from a transport perspective, as transport by boat is much more efficient per kilometre transported compared to trucks (which are used for short journeys). Similarly, smaller marine inputs do not always lead to lower emissions. It depends on how they are produced and what they are replaced with. Marine feed materials from the region were found to have relatively low emissions and contribute important nutrients.

It is clear that there is potential to reduce the carbon footprint of intensive aquaculture by using alternative protein sources. In the future, the study can be expanded to include other alternative Nordic ingredients and the results need to be verified through a longer feeding trial covering most of the production cycle and more environmental impact categories. One of the obstacles for this to be realised in the industry is that the availability of these alternative raw materials is still low. In a recent report calculating the climate impact of Norwegian farmed salmon, less than 1% of the feed currently consists of alternative feed raw materials.

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