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 (Fig. 1). 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.

Figure 1. Evolution of feed conversion ratio (left panel) and phosphorus and nitrogen loading to water (right) from rainbow trout farms at coastal areas of mainland Finland during 1980-2016 (source: Hannu Kallioniemi, ELY Centre, Southwest Finland).
Figure 1. Evolution of feed conversion ratio (left panel) and phosphorus and nitrogen loading to water (right) from rainbow trout farms at coastal areas of mainland Finland during 1980-2016 (source: ELY Centre, Finland).

Data of Figure 1

The figure is based on the official records of the Centre for Economic Development, Transport and the Environment (ELY Centre), a governmental authority monitoring the licencing of fish farms. The data consists of all the farms, around 150-300, that have been approved a farming licence at the coastal areas of the mainland Finland in each year (source: ELY Centre, Finland). To calculate nutrient loading, information on amount of feed used, nutrient levels of feeds, amount of fish growth, and nutrient levels of fish are used. Nutrient loading is the difference between nutrient delivered to fish and the nutrients retained into fish.

Specific nutrient loading reduced by more than 70 %

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 (Fig. 1). 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.

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.

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 further estimate the relative importance of these factors on the reduction in nutrient loading.

Rainbow trout families for AquaIMPACT experiments are produced at the selective breeding facilities of Luke’s Enonkoski fish farm. Photos: Luke.

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 (, 29.6.2019). The categories are determined by the estimated environmental impacts of the species.


Authors: Antti Kause, Antti Nousiainen, Heikki Koskinen (Natural Resources Institute Finland (Luke)


1- Jari Setälä, Kaija Saarni ja Jari Niukko. 2018. Kalamarkkinakatsaus 2017. Luonnonvarakeskus (Luke).

2- Knap PW & Kause A. 2018. Phenotyping for genetic improvement of feed efficiency in fish: Lessons from pig breeding. Frontiers in Genetics 9: 184.

3- Kause A, Kiessling A, Martin SAM, Houlihan D & Ruohonen K. 2016. Genetic improvement of feed conversion ratio via indirect selection against lipid deposition in farmed rainbow trout (Oncorhynchus mykiss Walbaum). British Journal of Nutrition 116: 1656-1665.