12 inches is about the max for the mudpuppy or waterdog as they are also called. They are a salamander that spends their entire life in the aquatic stage (as all others have a juvenile aquatic stage) They Have a full set of internal lungs ironically since of course they serve no perpose in the water. They (like fish) have gills however they are filamentous and protrude from either side of the head. Pretty neat Little critters... Never lined one, only see them while diving