I place the unknown fish in a 29 gallon tank that has a Banggai I know to be male. If he starts to beat the ^#%-! out of the new fish then I know it is also a male.
not an exact science, but i gues it works.
one of the cards is slightly larger than the other. the are often side by side (in a 180) and dont pick on each other, so im guessing that they are either a pair or two females...
