Scientists have recorded for the first time croaking noises from deep-sea fishes, says a report from the journal Nature.
Many shallow-water fishes are known to produce sounds used in communication, but this is the first time noises have been recorded from fish living at great depths (over 500m). The identity of the fish making the noises, however, remains a mystery.
The noises were recorded by Susan Jarvis of the Naval Undersea Warfare Center in Newport, Rhode Island, who was tracking sperm whales with underwater microphones called hydrophones. She recorded some unusual noises at a depth of 600m and consulted some experts to see if they knew what could have caused them.
David Mann of the University of South Florida told Nature: "Susan sent me the raw files for these sounds, and I immediately thought: 'That sounds like a fish sound'."
He estimated that the fish were around 20cm in length and that the sound had probably been produced by muscles in the swimbladder. The sounds are almost certainly a mating call for use in the abyssal depths.