its normal, they're just trying to figure out which is going to stay the male and which is going to switch to a female. it's a dominance thing. it could get quite violent at times, but they'll work it out.
Yep, its a dominance thing as stated, and don't get alramed if one start to real beat up on the other one, she is just letting it be known that she is the new top dog in the tank.