I keep grass Pickerel.
In three different tanks, the combination of Bowfin/ Grass Pickerel generated an aggressive posture from each of the Bowfins. This is very unlike Bowfin, but is clearly the most hated fish for all 3 Bowfins that I have ever seen.
I would go as far as to say that the only aggression I have ever seen any of my dozen or so bowfin apart from the Pickerel and co-specific aggression was an isolated incident with a green sunfish that constantly attacked him and well . . . it was graphic!
Reasonable success with Grass Pickerel and a larger tire track eel, Angelfish, Silver Dollars, Bichirs (I am not certain about Bala Sharks as one has died in the tank, and likely the result of the Pickerel, though I did not actually witness it).
Poor tankmates (or unexpected feeders if that be the case) have included:
large golden shiner minnows. I though them too large, but were devoured by the pickerels.
African Black Knives. I had to separate when one of the pickerel caught one. (Luckily the knife was only 1 inch smaller and I was able to "wrestle" it from the jaws of death.)
Salavini chases the pickerel and causes them to break the water surface. (The tank is a tall, but I keep the water at least 3 inches from the surface to keep the pickerel from hitting the glass lid.