Muscle fibres of the Japanese freshwater eel (Anguilla japonica) produce a fluorescent protein, the first to be identified in a vertebrate.

Atsushi Miyawaki and his colleagues at the RIKEN Institute in Wako, Japan, identified the gene that encodes the protein and named it UnaG, after unagi, the Japanese word for this eel. When expressed in mammalian cells, the protein produced green fluorescence. UnaG is inactive until it binds to the naturally occurring small molecule bilirubin, a breakdown product of haemoglobin. The team showed that UnaG can be used to measure bilirubin in human serum. It might also be useful as a laboratory tool alongside other widely used fluorescent proteins.

Cell http://dx.doi.org/10.1016/j.cell.2013.05.038 (2013)