Internal Fitness Tracker (IMAGE) Aarhus University Caption 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 behaviour. Credit Photo: Peter Grønkjær Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.