Some kind of sucker. Scale pattern and the oversized anal fin are the telltales here.
More importantly, it lets the hot oil contact the bones and soften them to nothing. With suckers/buffalo/carp, they are scored every 1/8” or so down to the skin. Ends up looking like a bunch of potato chips stuck together.
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You have to leave the skin on. Scale the suckers, but you have to cut the scales off of Buffalo & carp (called fleecing). Bleeding buffalo & carp is not optional- most commercial fishermen don’t initially, but then they have to “drain” the fillets for multiple days before selling it. Easier to just rip a gill and move on.
I’ll cut the bloodline out of bigger fillets, or if it’s noticeable. The section over the ribs doesn’t have y-bones and can be fried like a normal fillet, skin-off.
Redhorse and hog suckers are the best, on par with most panfish- there’s entire seasons centered around gigging & snagging them in the Ozarks. I’d rather have redhorse than crappie most days (but that might be nostalgia speaking). Good buffalo can be a close second, but it’s more similar to catfish in texture. Carp needs to be out of cold, crystal clear water (some people keep them alive and purge them for several days with water changes). Even then, it’s not as good.
Side note- if you get a grass carp over 20lbs, you can grill the loins and just pick out the bones.