my goldfishes

Hi,
i have 2 goldfish (and some other fish). the 2 goldfish have been circeling each other closly and chasing each other. i think the big one is the female and the smaller one is the male. the female is a diffrent goldfish its a red cap. the other one is a normal goldfish. can they mate? because the female has got very fat but has been like that for a while. is she pregnant or not because i wasent exspecting it . lol