jackalope's are real stuffed animals
billy bass is a funny thing for your wall, but it was never a real fish
WTF!? 5 months later? Get a hint.
The antelope and the jackrabbit are both mammalian herbivores with a similar body type, if different scales. A bit of tinkering might well allow for the creation of the jackalope.
A singing fish that can live outside of the water is quite different. We'd have to add lungs and vocal cords without compromising gill function, work out how it would eat, total mess.