One of the hippo documentaries on one of the cable channels showed various critters that live in the water with the hippos. One of them was a fish which was the narrator referred to as a freshwater shark. I’m pretty sure they said that it wasn’t a “true shark,” but they didn’t mention what its real name was. To me it looked more like a shark-shaped carp, mouth situated on the bottom.
Yeah, that would be my take. There are no exclusively fresh water sharks, but there are some that enter fresh water, and the bull is one of them. A bull shark swam up a river in MA in the early 1900s and got some folks swimming there.