I work at a pet store, not that kind, but a pet store never the less lol. By oddball, to my best assumption cuz a lot of pet stores dont carry cool fish, they mean like puffers, jack dempsey, electric blue cichlids, frontosa, peacock bass (its a stretch of the imagination but i have seen very few in stores) etc. It could also mean fish that they can only order during a certain season. I know with my store, we can only get certain fish during certain times of the year. Whenever the word oddball comes up, think more exotic/rare then what places usually carry.