Osopsaron formosensis is a bedazzling little fish that lives in the cooler waters of Japan and Taiwan. An unassuming little fish that sports neon colors throughout its body, the fish has a secret weapon to capture your attention if you haven’t already. Like a signal flag, the goby can erect, expand, and wave its sail-like dorsal fin to communicate with others of its kind.

http://www.youtube.com/watch?feature=player_embedded&v=QJAo8rUtb1g

In the wild, these gobies live partially buried in the sand, waiting for food to float by. Attaining a maximum size of 5cm, this gobies would make for the perfect aquarium fish if only they were obtainable. The dorsal fin flagging is a spectacular phenomena to watch as demonstrated by these two videos. The dorsal spine is first lifts up, and two black membranes expands on opposite sides.

What’s interesting is the dorsal fin appears to swivel around freely, by way of the fish controlling the direction it waves its fin at. We would love to share with you more about this amazing little fish, but unfortunately little information exists about the fish in the wild, and zero on the fish being available for the trade. Just goes to show how many gorgeous reef aquaria suitable fish are living out there, out of reach for the casual aquarist.