i guess it depends. my buddy had a fm that was about 3.5in and he bought another one and when that one was about 2in they started breeding. i have heard 4-5in before breeding. so i am not 100% sure. i have 2 that i am trying to breed.
Mr.Firemouth;1095333; said:At this point there is no way to differentiate if it is a submissive male or a female.
My recommendations are to allow them to stay together, increasing water changes to help in preventing secondary infections and promote breeding behavior, and continue observing the fish. If they swim together and any pits are forming in the substrate I would say it is a safe bet they are male/female and have paired.
If the larger fish holds a territory and continually challenges the other fish and chases it away then I would say you have 2 males.
HTH,Rich