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Game-, Reindeer- and AquaFood Research Program – GRAF :
» Consumer needs and expectations in the global markets
» Healthy, tasty, and high-quality food products
» Diverse and sustainable food production
» Changes in livelihoods and business sector competitiveness
» Projects 
  •Developing Reindeer husbandry and Reindeer meat market
  •Markets for products of captive fisheries
  •BENEFISH – the economic impact of the welfare of fish in European fish farming
  •Development of fish product quality research
  •Effects of live-chilling on product quality
  •Regulating the sexual maturity of rainbow trout in food fish production
  •Improving fish quality
  •The quality of European whitefish in the supply chain
  •Electric stunning of vendace
  •Action plan for sustainable aquaculture in Åland
  •Effects of location guidance on the fish farming economy
  •Environmental investment in fish farming
  •Diversifying aquaculture
  •Research on the selective breeding of whitefish
  •Research on production biology
  •New wave
  •Software for assessing the profitability of fish farming
  •Economic success factors of the reindeer husbandry  
  •Fish Consumption and the Catering Sector 
  •Utilization of less-valuable fish material in food, feed and bioenergy

Regulating the sexual maturity of rainbow trout in food fish production

Until recently, light manipulation has only been used in year-round fry production of rainbow trout. Now light treatments have come to be regarded as a potential tool for improving the fish quality. As fish mature, their quality deteriorates. If it were possible to control the timing of maturation, more fish of an appropriate maturity status, i.e. good quality, could be produced.

The goal of the project

The goal was to study regulation of the maturation of rainbow trout (Oncorhynchus mykiss) using light treatments. The effects of light treatments on maturation and end-product quality were evaluated. The light treatments were conducted with underwater lamps within sea cages at the Rymättylä Fisheries Research Station. Based on the experimental data, a statistical model was created for annual timing and duration of light treatment to delay maturation.

Photo: Kari Ruohonen


Administering light treatments with underwater lamps is a simple and cost-effective way to regulate the maturation of fish stock. Light treatments that continued from midsummer until the autumn harvest were observed to be efficient in delaying maturation and the deterioration of quality caused by maturation was efficiently prevented. For example, the fat content of the fillet, the colour of the muscle and the sensory quality of the roe and the muscles were better in fishes that had been subjected to light treatment. No negative effects in the production or quality were observed in light-treated fish when compared with control fish. Light treatments make it possible to lengthen the supply season of high quality rainbow trout. This has the potential to decrease the seasonal oversupply of raw material and attenuate price fluctuations.

Scientist in charge of project

Kari Ruohonen
Turku Game and Fisheries Research
Itäinen Pitkäkatu 3
FI-20520 Turku, Finland
Phone +35820 575 1681

Other research staff: Susanna Airaksinen, Tarja Aro, Markku Vaajala, Antti Forsman, Olli Norrdahl, Jari Riihimäki


Finnish Fish Farmers’ Association, University of Turku: Department of Biology, VTT Technical Research Centre of Finland, Kalaset Oy, Kalaliike V Rantamaa Ky, Kalastusyhtymä Valtanen, Apetit Kala Oy, Heimon Kala Oy, Finnish Freshfish Oy Kalamesta, Ab Chips-Food Oy, Hätälä Oy


Duration: 2003–2005

Text version

Jaa Jaa

© Finnish Game and Fisheries Research Institute.Modified 2009-7-6