Belgian fish biologists studying tilapiine cichlids have discovered what they believe to be an entirely new way it makes sound.
The team, from the University of Liege’s laboratory of functional and evolutive morphology, filmed the Nile tilapia (Oreochromis niloticus) with sophisticated high-speed cameras.
They shot the fish at 500 frames per second, while a technique called cineradiography produced an X-ray like film at some 250 frames per second — and the sounds they made were recorded by an underwater microphone.
By analysing the movements of fish when they generated their sounds, the scientists determined that territorial males used a backward movement of the pelvic and pectoral girdle — a bony structure that supports the pectoral and pelvic fins — and movements of part of the anal fin to do so.
They believe that the male cichlids contract a group of muscles that compress the ribcage and swimbladder, resulting in movement of the fins and generation of sound when the swimbladder deflates.