From what I've read, most fish have very specific behaviours that they are pretty much programmed to respond to, so even if another species, to us, looks very similar, chances of it actually having the same behaviours and responses to signals is very small.
It's pretty rare to find to find any type of hybrid fish in the wild even if they all live in the same area.. and even in captivity, it's not all that common either. In captivity though, some fish, if they can't find a mate of their own species, may take another species instead. Usually only happens with live bearers who are relatively closely related. Guppy and molly, for example or sword and platy.. you rarely hear of other hybrids unless humans have meddled to make it happen.
