I bought mine at a Petsmart for $10USD each and both were already 3 inches long. They were housed together for at least 3 weeks at the Petsmart until I finally finished cycling my tank and picked them up. They never fight, but one of the Ctenopomas do rub bodies and tussle with one of the Nandus I just picked up last weekend. Your Ctenopoma looks great too! I can't wait until they get full size! Should be real impressive.
Brian