Fatih, one might not do much population reduction in a 6 ac pond, but if you see one, there could be many more swimming around. You rarely see all the fish in a pond, especially a larger pond.
Different species of catfish have different feeding habits. I don't know of any catfish here that when over 5 pounds feeds only on dead things. They feed on live fish.
Think about it for a minute. For a fish to get large, it needs to eat a lot of food. Bill Cody in another thread said that one Walleye will eat 1,000 minnows a year. There are a LOT more live fish swimming around in any pond than there are dead fish, so it just stands to reason that a fish will target the most available food source - which is live fish. I'm not saying that catfish won't eat a dead fish, but the larger ones will eat more live fish than dead ones.
Same goes for Largemouth Bass. I've caught a number of LMB while fishing with dead and cut up fish. But LMB aren't thought of as eating dead fish. Northern Pike too. A good technique to fish for them is to fish with a dead fish on the bottom in shallow mucky bays in the spring just after ice out. They cruise along eating the winterkilled fish. Again, that's an example of fish targeting a readily available and easy food source.