New Pleco with unusual behavior...

I purchased what I believed to be a l029 called a galaxy or vampire Pleco. Since I have had him, i haven't seen him use his caudal fin. He didn't use it at the fish store either. He just shuffles around with his pectoral fins for food and hiding places. Even if I touch him with my hand, he refuses to use his caudal fin to escape. do any of you know of possible causes of this behavior besides his back being broken? (Please don't be a broken back!)

Could be female where they don't use it much? What happens if you take her out of water, fin come up while you hold the head with thumb over mouth and fingers holding the head?

What are you looking for if I do it? Tail motion? Raising of the dorsal fin? I just want to know what to keep an eye out for when I try it.

They usually instantly stiffen up, all three prongs of fins out as a defence.

He did stiffen up both pectoral fins and the dorsal. But was there anything else you were looking for?

Nope that's it, if he can stiffen the dorsal then the back is fine. Perhaps its a slight malformation in the breeding and will never stiffen up? I've had old pleco's with the entire caudal bitten off and they do just fine without one.