Feeding practices, feed development and genetics have reduced nutrient loading of rainbow trout farming by over 65 %

Photo of author

By Milthon Lujan

In Finland, 47 million kilos of Atlantic salmon and rainbow trout are consumed annually. Only around 23.4%, that is 11 million kilos, is produced domestically(1). Reducing the environmental impact is a key factor for development of sustainable food production. In Finland, nutrient loading of aquaculture has been successfully reduced during the last decades with better feeding practices, feed development, animal breeding and other actions.


Feed conversion ratio (FCR) is the ratio of feed input to fish biomass outputs. The FCR value of 1.1., for example, means that to produce 1 kg of fish, 1.1 kg feed is needed.

During 1981-2016, FCR has been reduced by 47% at rainbow trout farms located at the coastal areas of the mainland Finland. In 1981, FCR was 2.01 and in 2016 1.06. To produce 1 kg of fish today, only half of the feed is needed now compared to 80’s.

Feed costs cover around 35-45% of the total production costs, and FCR is a major determinant of nutrient loading.

Nutrient loading reduced by more than 65 %


Nitrogen and phosphorus are main nutrients that micro- and macroalgae need for growth.

Elevated levels of these nutrients in the aquatic environments cause eutrophication.

Nutrient loading from aquaculture can be quantified as the amount of a nutrients ending up in water (kg) per produced 1000 kg of fish. Similar to FCR, environmental loading defined in this way quantifies the ecoefficiency of aquaculture operations.

From the peak year of 1981, phosphorus and nitrogen loading from rainbow trout farms located at coastal areas of mainland Finland has been reduced by 76 % and 70 %, respectively. In 1981, loading of phosphorus was 16.0 and of nitrogen 125.6 (t/kg). In 2016, the values were 3.8 and 37.8, respectively.

See also  Fixing the role of nitrogen in coral bleaching

Such an improvement in resource efficiency is a win-win for both industry and environment – the same amount of food can be produced with significantly reduced amounts of raw materials and reduced environmental impact.

It is good to note that total nutrient discharge is determined by the total amount of fish that are farmed and the nutrient loading per produced fish kg. At the mainland coastal areas, total discharge reached the peak in early 90’s. After that it has declined by 74% for phosphorus and 66% for nitrogen.

Which factors have reduced nutrient loading?

Nutrient loading has been reduced by several factors:


Feeding practices and farm management.
Feed composition and raw materials.
Genetic improvement in FCR by selective breeding programmes. FCR is known to improve when rainbow trout are selected for rapid growth and favourable body composition(2,3).
Potential changes in the environment.

AquaIMPACT project will estimate the relative importance of these factors on the reduction in nutrient loading. https://www.luke.fi/aquaimpact/ 

WWF recommends rainbow trout farmed in Finland for consumers

WWF has produced recommendations that guide consumers towards sustainable consumption of fish species. The guide has ‘traffic lights’ for each fish species. Species have been classified into green, yellow and red categories. Species on green are recommended, on yellow to be consumed prudently, and on red avoided. Rainbow trout that is farmed in Finland is on the green category (wwf.fi/kalaopas/#kirjolohi, 29.6.2019). The categories are determined by the estimated environmental impacts of the species.


AquaIMPACT project

AquaIMPACT (Genomic and Nutritional Innovations for Genetically Superior Farmed Fish to Improve Efficiency in European Aquaculture) is an EU-funded innovation action that develops technologies and services for European aquaculture. These technologies are based on selective breeding, genomics, fish nutrition, and digitalisation. The multinational consortium consists of 11 companies and 13 research institutes from 9 countries. The project is coordinated by Antti Kause from Natural Resources Institute Finland (Luke). More about the project can be found from the website. AquaIMPACT Newsletter can be subscribed from here.

See also  SimSaLipiM: A Modeling Tool for Formulating Sustainable Salmon Feed

The project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 818367.

Antti Kause
Principal Scientist
tel. +358295326222

Source: LUKE

Leave a Comment