apnate:

You would have to help them along if it is even possible. When fish spawn, the eggs have receptors on their surface where the sperm of the same species can attach. This receptor is like the lock on your door: only a specific key can fit in and work to open the egg’s vitelline envelope to allow the sperm to enter. Therefore, when a largemouth bass sperm encounters a yellow bass egg, nothing happens because the sperm does not have the suitable surface protein to fit onto the egg’s receptor.

Even if you managed to cross-breed the two in a laboratory setting, the offspring would almost certainly be unable to create offsring of their own. The definition of a species is a group of organisms that can mate and produce fertile young. Largemouth and yellow bass are two separate species, so while you may get offspring (and that is not a guaranteed success), they will almost certainly not be able to establish a thriving species. If the two fist were just different breeds of the same species, like a pet dog, then they could reproduce, but largemouth bass (Micropterus salmoides) and yellow bass (Morone mississippiensis) are not even the same genus, much less species.