I think you should stock what you want, if it isn't invasive. Can you tell a mudpuppy from a salamander larval stage? http://gfp.sd.gov/wildlife/critters/amphibians-reptiles/mudpuppy-tiger-salamander.aspx some more info, unless you don't have salamanders in NJ.

- Grundulis..I have seen ponds with crazy amounts of frogs, mostly bullfrogs, I mean, standing in one spot and counting 15+ without moving