Will the two fight? Or pair up and be nice to each other. Im sick of trying to find a fish that would not get attacked by my female GT. It's a juvi and in a 60g.
They might fight. They might not. If the male is ready to breed and the female isn't, you could see a fair bit of aggression. Use a divider. It's the best way to introduce a female.
Sorry just re-read that. It's difficult to guess sex as juveniles. I once had 2 4 inch GT's that I was sure were male till they both started laying eggs. Very hard to tell when young until they pair up and breed.