Channel is definitely ruled out. The Anal fin says Columbian shark. Most Columbians are always swimming unless of course they're stressed which he probably is due to the lack of salt in the water.
Could be worth asking that LFS if they'd pay for him or at least take him off your hands. Sadly a lot of people would say he's worthless since he appears to be scared. I'd pay good money for him if I was set up properly.
Yeah from what I can see he's very stressed and might have some scars from sores due to being in freshwater instead of brackish.
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Don't know how it's alive but I'm almost sure that's a columbian shark. You can see the nice white/silver trim to the anal fins. Channels don't have that at any point in their lives from what I know.