HOIST THE SAIL !
Sailfin Blenny (Emblemaria pandionis, male), Roatan, Honduras
The dorsal fin can be flicked up and down with different rhythms in order to communicate, to defend territory in front of other males, or to approach and seduce females...
Olympus OMD EM5 MkII, Zuiko 60mm Macro Lens, Subsee +10, Nauticam Housing, Dual Inon Z-240 Strobes. Settings 1/125, f/20, ISO320