sexing

[icecube]

Hi,
I have two 4.5" FH.
how do i sex them.i tried to use the venting method but its difficult to sex the at such a small size.
one of the FH has a black spot on its dorsal fin and another does not have it.
they are in the same tank and show very little aggression towards each other.
lately the FH with the black spot has been bullying the other one.
Is there any accurate method apart from venting to sex them.

 

[silvergrayhair]

the fool proof way is to wait for the fish to lay eggs. by then, there would be no doubt that its a female