A 55 is a little small for a betta IMO, but you could get away with it. They will eat small shrimp and small fish. My dad's ate his neon gobies and firefish. They stay hidden if the rocks most of the time, but will eventually get a little bolder. Took my dad's fish about a year to swim around with the other fish more. Make a cave or arch out of the rock work. My dad's likes to stay under an arch in his tank looking out the front at people. You also have to be careful about the other fish. They can starve if the other fish are aggressive eaters. They will eventually get less shy and eat more, but at first the food pretty much has to be right in front of their face before they'll eat. Hope that helps! They are really cool fish!