You got ripped off by big al's Death Sting. Both fish that are labeled as p. congicus and p. retropinnis are both p. polli. I have seen them both a month ago. The one that is so called p. retroppinis are skinny p.polli. The patterns looks very similar to a p.retropinnis but the head shape is not the same as the p.retropinnis. You got ripped off buddy. A 6" p. polli only cost $35 in BC.
It's funny that the owner knows his stuff. I talked to him before and he couldn't even answered some of my questions and just making up stuff. I was just pretending to agree on what he was saying because I don't want him to feel bad, plus I needed the discount. Lol!
How to tell a p.polli from a p.retropinnis is by looking at the head. P.polli have a pointy snout while p.retropinnis have a wider snout similar to a p.weeki if you look at from the top view. The finlets of the p.polli also starts from the mid body, while p.retropinnis start a lil' bit lower from the mid body.
Continue feeding that bichir and it will reveal sooner or later that it's a true p.polli. I actually bought 2 myself, but I knew it was a p.polli. I only bought it because I like the pectoral fins as it got some lil' stripes and not commonly seen in some captive breed p.polli from other lfs.