Is it a dragon goby (also called a dragon fish, or a violet goby)? Long eel-like fish with a really big mouth and neat looking fins running the length of it's body? I had one of those and he was perfectly happy with bloodworms and brine shrimp. If it is one of those and you have it in with other fish you have to make sure they're actually getting food, as they're usually not super active and they have really small eyes and bad vision so it's often hard for them to find the food.