I have two percula clownfish and have had them for about 2 years. Just recently one has grown larger and darkened in color(Female?) before now they would never venture more then a few inches from each other but for the last few hours they stay apart. I've seen one of them go to their normal place and kinda open and close his jaw wide and very fast...stay for a sec...and then leave....The only noticalbe thing is I lost a yellow tang the other day....It did not expire in the tank though....Whats up?