I know that Festae can be downright brutal when it comes to choosing a mate. That's what RRgers is getting at. If the Synspilum isn't strong enough to stand up to the Festae, it could end badly for it. Best to have a divider or spare tank on hand just in case you have to intervene. But I'm not even sure this is breeding behavior or if it's even possible for them to cross. If they do manage to spawn successfully, it would be the first time that I've seen it. I worry about that rock ledge also. They barely touched it and it wobbled. May want to secure it a little better before a fish is injured.