This is a coelacanth: the enormous living relative of the first fish that crawled onto land about 410 million years ago. Now another link to its land-loving ancestors has been confirmed: the coelacanth has a lung.
Paulo Brito from the Rio de Janeiro State University in Brazil and his colleagues used X-ray scans of the fish to create 3D reconstructions of the suspected lung. They also imaged the organ in fish of different ages.
The team found that the embryo has a well-developed and potentially functional lung. As the coelacanth matures, though, it stops growing and clearly becomes vestigial. A fatty organ that controls buoyancy was seen to develop in parallel. These findings suggest that ancestors of the fish once used lungs to breathe, later adapting for life in deeper water.
Coelacanths were thought extinct until one was discovered off the coast of South Africa in 1938. They are shown here at a depth of 130 metres in nearby Sodwana Bay.
Although the fish now have symmetrical fins, they were once asymmetrical, just like those of our fishy ancestors. Recently, details of their sex lives were also uncovered, showing that they are serial monogamists.
Journal reference: Nature Communications, DOI: 10.1038/ncomms9222