Beware the slippery slope... If "trade" occurs in one state and both animals are legally posesed no permit is required. If interstate commerce is entered into a trade might well fall under the umbrella of the term "barter" which after all is a form of payment. A legally held animal can be gifted to or lent on a breeding loan without a permit, or move with it's owner in the case of a move of residence. A trade of two Indigos might fly based on the previous writer's comments while a "Salmon Boa" for a Indigo sounds like a sale albeit shrouded in grey. Best obtain info from the appropriate federal agency and print out same if it's what you're hoping to hear. Only need to be concerned with state restrictions in those where the animal historically is native.