Ok this is what is going on in you pond. You probabaly haven't removed enough bass over the years and there are so many of them in there that they ran out of food. The bass that are big and theres probabaly on two or three of them in the whole pond, Have been surviving by eating some of the smaller bass. All of the bass in the pond have stunted out from lack of food and only get enough each year to survive. It takes 10 pounds of forage for a bass to gain one pound. The catfish eat lots of different things plus bluegill and other fish they can fit in their mouth. If you want the pond balance you need to start taking out some of the smaller 8-12" bass and some of the catfish. Maybe even add some more bluegill or some other type of forage like threadfin shad. Just my 2 cents worth but ive been dealing with a pond in the same situation and almost have it straightened out.