[Harmless Teddy Bear]

But most of those are ocean fish. We are talking inland fresh water. So except maybe for trout not a lot of fish with fat.

Also fresh water fish tend not to swim in schools so it would be more of a challange to catch them.

[piasa]

Salmon and eels travel inland from the ocean. No need for fish ladders then.

Scavengers and, if they had dogs, would have consumed and carried off any fish bits that were discarded. If they did fish during runs they probably cleaned them on the spot , maybe right into the water, and the remains would wash away.
What fish they took back to camp would be gutted and deboned so there wouldn’t be much evidance even if they were big fishermen.