There are naturally occuring hybrids if that's what you're asking. The closer in relation to each other the seperate species are the easier they will hybridize, and might even be able to produce viable offspring. The further apart they are, the less likely they are to hybridize. Lets say you cross a rtc and tsn(hehe) they are closely related so you might get a 50% success rate when combining them. Now when you take a tsn and hybridize it with a niger catfish that might drop to something like 5-10%. These are not actual numbers, but you get the point. The way that most hybrids are created is just by simply mixing the sperm and egg of two different species in a container. They do the rest on their own. It's too costly to inject every single egg that makes a hybrid. Therefore if they couldn't do it on their own then it wouldn't happen at all. Hope this makes some sense.
