Friday July 7, 2023

Science Daily

The pronounced seasonal changes of warm open-water and cold ice-covered seasons dominate natural cycles in Finnish lakes.

“Summer is the growing season of fish followed by weight loss during winter and spring spawning time” says research team leader, Professor Kimmo Kahilainen from the Lammi Biological Station, University of Helsinki.

Significant changes in temperature and other environmental factors during colder months result in lowered metabolism in fish. Additionally, less food is available for fish during this harsh timeframe. Under these conditions, eventually the energy required to grow is not met by the amount of energy taken in, resulting in weight loss and starvation.

This seasonal cycle means that fish mercury in winter and spring can be up to 30-40% higher compared to summer and autumn. Differences are pronounced in fish feeding on other fish, such as perch and pikeperch, which are important species for both recreational and commercial fishing in the boreal region and continue to be staples in regional dishes. Despite the higher mercury found during these seasons, all fish species in studied southern Finnish lake were below the fish consumption health limit (0.5 mg/kg) for mercury.

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