BBJR, the predators you keep are a personal choice. You are correct about them occupying different niches. However, they all breathe the same finite amount of oxygen and, when feeding, will leave their niche area to jump on some groceries. I always try to err on the side of too much forage since they can be double tough to re-establish.
Every fish in the pond, even the forage fish, is a predator on some other smaller fish. Mostly, they prey on their own species. Open water predators like the HSB feed in the shallows when they don't have open water prey to clobber. And, a CC over 2 pounds is is a top of the line predator.
I think of a pond as a pasture or even a forest. An increase in the rabbit population means more coyote survival until they eat all of the rabbits. Then Mama Nature reduces the numbers of predators through natural selection. Too many deer or cattle mean habitat destruction after they overeat their forage with the land suffering when the forage is denuded. Like fish, cattle and deer prefer different forage and occupy different niches but will cross to the others forage base when necessary.
The predator/prey balance is a constant concern for a pond owner who wants a well managed pond. Too many fish in a pond causes water quality problems and Mama Nature always gets even.
