I think some plecos look more like sharks than some of the fish labelled as freshwater sharks...but they typically stay on the bottom of the tank and aren't active swimmers.
...but i've never owned freshwater sharks, so, can't offer advice on them. But I recommend plecos in addition to what you get
Columbian are a brackish water species. They can be kept in fresh water when small but need to be accimilated to brackish as they grow. And then to full marine as full grown.