The fish is definitely a c. apurensis, I recently sold one that grew to 20" and was still growing. I've seen 24" specimens and have read of 28" monsters. One of my all time fave's. I paid like $125 for mine @ 5". I tried to sell it for almost 3 months on this site and one other for $250 with no takers,(it was for PU only) finally had to almost give it away for $50 as it too outgrew it's tank. Since they have to be kept alone or with very large fish due to their agressive nature it's hard to find a home for them. Buy a 300g and keep it if you can!
Yeah they do get expensive, and at the size you have yours at it's going to be a lot more. But you don't always sell them with such a high price, because not very many are willing to pay such a high price.
Great looking Catfish though!!