Ribbon eels (Rhinomuraena quaesita) are a species of moray eel that are sequential hermaphrodites. Starting out male, juveniles are black with a yellow dorsal fin. Adult male eels (the subject of this photo) are bright blue with a yellow mouth and dorsal fin. Eventually they become females and turn entirely yellow.
Lembeh Strait, North East Sulawesi, Indonesia
Canon EOS 7D Mk II, Canon EF 100mm f/2.8 macro USM, 1/250, f/16, ISO 200, Inon Z240 strobe, backlit with a narrow beam of light produced by using a Retra Pro Light Shaping Device fitted to the strobe, handheldby Ross Gudgeon