Are my goldfish fighting or playing?

hi, i just got two fantail goldfish today, and they have been fine, but off and on they chase eachother and such, i dont know if they are playing or fighting and it scares me. they are in a 2 gallon bowl, and it seems roomy enough for the both of them, the man at the pet store said it would be fine too. so help!? are they fighting, playing, mating, getting to know eachother, what!? thanks so much for help!