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Danish researchers have now shown that fish such as cod move around with an internal fitness tracker that continuously logs information about the fish’s metabolism. Information is recorded in the calcium structure in the fish’s otoliths and can be used to gain new knowledge about how changes in the marine environment affect a fish’s metabolism and behavior. Photo: Peter Grønkjær.
The fish’s fitness tracker. The carbon in fish otoliths comes from two sources, partly from the water in the form of dissolved inorganic carbon (blue bullets) and partly from the food burnt off as part of the fish's metabolism (red bullets). Carbon from the two sources is diffused into the fish’s blood. When the fish’s metabolism increases, the proportion of carbon from the food increases, and there will be more "red bullets” in the blood supplying the carbon to the otoliths in the fish’s inner ear. In this way, the growth rings of the otoliths continuously record record information on the fish’s metabolism in the form of the so-called delta 13C value. Illustration: Ming Tsung-Chung.

2019.01.18 | Public / media

Otoliths - the fish’s black box - also keeps an eye on the metabolism

For the first time ever, an international research team has shown that fish otoliths record information on fish metabolism. Analyses of old and new otoliths can therefore provide new knowledge about how different species of fish adapt to new conditions, including climate change.