Observations: Tiger Grouper Behavior

Why is this fish swimming above the coral head?

Lately I have been reading about mimicry in fishes, which has prompted me to locate a bit of video I shot in the Exumas during a REEF Field survey a few years ago. When I dedicate a dive to a fish survey, I carry my video camera to help substantiate any identification that I’m uncertain about. On this particular dive, I noticed a small yellow fish swimming around the base of a coral head then up into the water column. It got my attention because it didn’t quite behave like the intermediate Blueheads (Thalassoma bifasciatum) in the vicinity.

Ned took a look and I shot a bit of video, although whenever we got too close, the fish would flee back down to the coral head. We backed far enough back to allow it to resume its behavior and watched – it looked like it was picking plankton! Back on the boat, we discussed this strange behavior of the juvenile Tiger Grouper, Mycteroperca tigris, a fish we had always seen down close to, or in the reef.

I promptly forgot about it until this week when I was looking for references about mimicry in fishes. There are several grouper species that have been observed, in their juvenile stages, to mimic other fishes and there is a paper that might explain what we saw: Mimicry of initial-phase bluehead wrasse, Thalassoma bifasciatum (Labridae) by juvenile tiger grouper, Mycteroperca tigris (Serranidae) – Snyder 1999. Now I wish we’d spent more time watching this little fish!