I'm a newbie pond owner. I have a small pond, about 1/2 acre, with some catfish and minnows. I'm not sure exactly what kind of catfish I have, but I think I have a few types. I've had the pond for about 7 months now and all was fine until recently I noticed the water would look a bit dark at times, kind of like it was muddy. And today, about 20 catfish are dead on the surface, with a few that are moving. We feed the catfish once on a daily basis and have a pump that circulates the water. What could be causing the fish to die? What should I do?! Please help! Any info is much appreciated!

Julie, there are no absolute answers without a professional analysis of the water. Are the fish that are still moving coming to the top to get air? If so, it sounds like a dissolved oxygen crash. You say that you have a pump to circulate the water. What kind of pump and where does it circulate from and to? If you are picking up water from the bottom and bringing it to the top, you may be forcing low oxygen water to the top. If you're just moving the water from one place to another, you're really not accomplishing much. Others might be better at answering this.

You might have too many fish for the size of the pond. Or possibly some sort of disease.

You are better off using an oxygen pump for aeration. Look at the thread on this site to learn more about aeration.

The easiest way to check for low oxygen levels is to go to your pond at sunrise and see if the fish are at the top gasping for air.
If it is an oxygen crash, the best emergency aeration is to take water from close to the top and get a good splash as it falls back.
Like Dave said, you probably have too many fish for your pond. You can read from this site about too much decaying matter and algae sucking oxygen.
One last thing, are there any fields with poisons or cows with fly poisons that could be getting into your pond?

I have an oxygen aerater with a 2HP pump. There are no fields with poisons that I know of and no cows nearby.

The tiny minnow fish seem to be fine. I took out some of the fish that were slightly moving and put them in a little kiddie pool with fresh water and a pump. After a while, 3 or 4 started swimming and I threw those back into the pond.

Based on that, I guess y'all are right on about the oxygen. The doctor at the local fishery diagnostic lab said it might be a gill parasite or something, but I wasn't able to make the drive all the way there with the fish to have them tested.

I hadn't noticed any problems with the aerator but I had my brother come over and take a look at it just in case. He said it's fine, but I've turned it on to work non-stop now. It was on an automated control before. Maybe the control's not working properly? That's our best guess at this point. I'm just keeping a really close eye on it.

Do ya'll know of any way I can test my pond water or somewhere I can send it to get it tested? Just in case there is something bad in the water (that might also seep into the water table), I'd like to get it checked out.

Thanks again!
Julie

Julie, an aerator should keep DO problems from occurring.

I suspect something in the water. If fish revived in the kiddie pool, that's a pretty good indicator. Will the local fisheries diagnostic lab check the water? I expect they will. Get a new baby bottle and take a sample. Get on the phone to them and get it there ASAP. Be sure to remove the dead fish from the water and dispose of them. As long as you need to test water, I'd haul a dead fish along.

Catfish can handle low oxygen levels better than most other fish species. I have a pond about the size of yours, and have had as many as 700 catfish in it without a single loss due to oxygen
depletion. And, I have run only a small aerator for the last couple of years. My guess would be disease or something toxic in the water. I know that acidic water conditions can be deadly for catfish. Of course, I'm only speaking from my own experience and certainly not as an authority on the subject.