Question
We have had a vacation home in the Catskill Mtns. for 25 years. About 12 years ago we dug a pond 60' long by 25' wide. It is 10' at its deepest. It's fed by natural spring water, supplemented in the summer by water pumped from an uphill well. The only outlet is a screened drainpipe too fine for fish to get through. We haven't tested the water, but it's aerated 12 hours a day and crystal clear and from the same source as our house water which we have drunk for 25 years without ill effect. 10 years ago catfish showed up, presumably delivered as eggs on bird feet. Frogs also settled in, and we get an occasional turtle. Up until last summer scattering a handful of Rise fish food would bring dozens of catfish to the surface. I estimate we had a hundred or more, up to 10 inches long. This year, there are no catfish. The pond seems otherwise healthy - teeming with tadpoles and minnows. We are completely baffled at the disappearance of the catfish without a trace. Over the years we have had an occasional heron, fox, or other predator that has removed a fish or two, but nothing on this industrial scale. The pond is isolated from potential human predators. Can you suggest a possible explanation for the mass disappearance?

Answer
That is a tough one.  My best guess is that a disease came and wiped them all out.  Catfish are a pretty social fish and they are also quite susceptible to bacterial infections.  This leads to extreme susceptibility to communicable diseases.  Without being able to tell you what strain of bacteria are responsible, I can only offer that it pretty much had to be a disease to take out that many fish so quickly.