They are very shy fish and hide more than they are out. It does good in a reef tank but will eat small crustceans and smaller fish that will fit into their mouths.
I had one years ago its a gorgeous fish but I wont get another because it was very rarely out and I like to look at the fish I purchase.
some other info
The Marine Betta or Comet is difficult to keep mainly because it needs special attention in order to eat. Although there may be cases where this fish will eat prepared foods, we have not seen it. Normally they will only eat live fish about the size of a guppy or very small goldfish.
They do not tolerate fish of the same species at all and will fight to the death.
They also need plenty of time to stalk and capture their prey. If they are in a tank with other predaceous fish, like lions and groupers, they will most likely starve because they are not fast enough to get a good share of the food.
The Marine Betta is a beautifully colored fish with large fins, which are a continuation of their body color and give a rounded appearance. These fish are very dark with many white spots covering their body. They also have a "false eye" in the upper rearbody. Marine Bettas are not aggressive towards other fish of the same relative size. Great for fish-only or aggressive tanks. They should not be kept with shrimp that they will mistake for food. They are great for fish-only tanks.
Mike