Scientists have discovered a new method for examining sex lives and migration patterns of fish - by looking in their ears.
By studying ear stones in fish, which act as tiny data recorders, scientists can now reveal what areas of the oceans the fish have been visiting and insights into their sexual behaviour.
The information could be valuable to scientists, conservationists and fishermen as they attempt to manage fish stocks and require information on the movements of fish in the wild.
Tiny ear stones called otoliths, which are in all bony fish, store chemical elements picked up from the surrounding water.
As fish migrate, changes in the ambient water chemistry are recorded in the otoliths, but it is difficult to translate these signals into records of fish movements.
Now researchers say they have created a translation dictionary revealing what the different chemical elements stored in the chemical makeup of the stones can tell us about the environments fish have travelled through.
The research, conducted at the University of Southampton and the Centre for Environment, Fisheries and Aquaculture Science (Cefas) in Lowestoft, involved raising plaice in an aquarium for one year while measuring the chemistry of the water and the fishes' blood.
At the end of the experiment, they compared the water, blood and otolith chemistry to better understand how elements become integrated into the growing otolith.
Clive Trueman, co-author of the study and associate professor in marine ecology at the University of Southampton, said: "These otoliths can now be used like the Rosetta Stone - allowing us to read the story of fish migrations from the chemistry of their ears.
"We also found that sex can interfere with the chemical signals. This complicates the job of translation, but provides us with new information about the biology, and private lives, of fish at sea."
The study is published in Methods in Ecology and Evolution.