Thanks for your responses. Answers to questions:

Sunil: Yes, the catfish are 3 to 4 years old (6" long when stocked). I stocked 150 channel cats and 50 blue cats. 6 months ago I caught a couple of neighbors poaching the pond. They caught a bunch of fish and 20 of them died - gut hooked. So of the original release, about a quarter of them have now visibly died.

FishinRod: Very limited opportunity to spawn in the pond. A few logs on the bottom and I have seen what look like smaller catfish at feeding time. There are bullheads in the pond though so I can't say for sure that the stockers have reproduced.

esshup: The only catfish that I am aware of having been harvested are the 20 fish that the poachers killed. So before this die off, there were a possible 150 to 180 of the original stocked fish still in the pond.

So I fed normally yesterday just before sunset. The sunfish, golden shiners and gambusia fed enthusiastically. No sign of any catfish and very significantly, no turtles coming to the pellets. There are usually 20 red eared sliders gulping pellets but none showed up yesterday. Both air and water temps are relatively low so I wouldn't have been surprised if the catfish were somewhat lethargic but I never expected a complete catfish no show. What are your thoughts on the possibility that all catfish are dead and most have settled to the bottom?