The smaller ones vent goes back but the bigger ones vent hooks forward. They're definitely different that's why I figured the bigger one was a female. They are staying in a 33 gallon long divided until the little guy was big enough to handle her cause she used to fight with my 10 inch gt witch from what I read was to make sure he was strong enough to mate with cause I guess flowerhorns the female is usually the aggressor. Then I was gonna introduce them both into a new 75 gallon or bigger to have a breeding pair. Although they are in a small tank right now I have it well over filtered and they're in my smoking room right next to my chair so they are always at the glass begging for food and get lots of attention. The dirtiness is this fricken alge that I can't get to stop growing everywhere. Any advice would be great