Cokeman,
I run into this all of the time. Some fish hatcheries are more interested in selling you more fish than you need because they want to sell fish. You can look at the reason for the fish kill from different perspectives, but had you had fewer fish (lower oxygen consumption) it probably wouldn't have occurred- more on this later. Ultimately, oxygen consumption exceeded production. The dyes you used also inhibited production of oxygen from phytoplankton. Ewest, I politely disagree with you but the chemical application made two months ago probably had little influence. I say this for two reasons, 1) it was two months ago, 2) copper concentrations and the ability to kill perish quickly in our hard waters of the midwest. Also, filamentous algae doesn't have a lot of biomass associated with it (i.e. you can kill a lot more suface area of filamentous algae in one shot than you can a submerged plant). I would refrain from using dyes, though. If you really want to grow some fish and ensure some good "free" oxygen from phytoplankton then I would cut back on the dye. See how you can look at this from two ways??? if you had fewer fish then less consumption or had no dye then more production from phytoplankton. The bottom line is that the conditions were just right to cause disaster. From my expereince, a stocking rate of 467 catfish/acre (you had 700 in a 1.5 acre pond) that are getting fed regularly is a HUGE risk for a midwestern farm pond unless special circumstances apply (water exchange system, high oxygen agitator- more on this later). This is especially true in the heat of the summer.
I would also predict that your fish were weighing between 3/4 and 1 lb given the 10-12" size class of feed trained catfish. This really boosts you're biomass. In the midwest, most ponds support and we are safe at 250lbs of fish per acre and should not exceed 400lbs without some serious aeration (for farm pond fisheries). I'm a huge fan of bottom diffusion aeration, but it is not near enough for heavy feeding operations with lots of fish/acre. I'm not even going to pretend to know how much you were feeding but I am not surprised that you had a kill even with the windmill diffuser. Aeration has its place, I use it all of the time (electric units), but it is false security for guys trying to grow big fish in small ponds with agressive feeding regimes. Just read some posts on this site. The best pondmeisters this website has (probably in the nation) have gotten burned from oxygen related issues. Sometimes the kills can't be prevented, but you can stack the odds in your favor. Surface agitators are the only way to go if you really want to push the carrying capacity envelope. You can do more than normal with a bottom diffuser, but you can do a lot more than normal with a surface agitator. Most of my clients have bottom diffusers and feed lightly-moderately. The guys who feed pretty heavy have surface agitators- sometimes with diffusers.
The fact is that shallow heavily vegetated ponds are more susceptible to fish kills. It's also a fact that ponds with lots of fish that are fed regularly are also more susceptible.....just read some of the posts on this site. This is not to disuade from feeding, but guys who feed a farm pond like it was a hatchery pond will almost always pay the price.
I'm sure lots will disagree with me on my last comment, but I contend that some people forget what "supplemental" feeding really means. It's easy to do. It's easy to get excited and want to feed more and more and more. Just be careful. Remember, these are farm ponds not fish hatcheries.
Also, our BOD in the Midwest can be naturally high because of the fertile nature of our soils and the agricultural use of many of our watersheds. If you are going to feed your catfish regularly and have other fish species, I would stock no more than 200 CCF/acre. I really like to see 50-100 CCF/acre, though. This is especially true if you also desire a decent bass fishery. Don't forget about harvest!!
I certainly agree with Ewest in that you found your limit. Ewest also made a great point that a lot of people forget about.....think about the pond when the fish are grown. Feed your fish and have fun. Be sure to cut things back in the heat of the summer. Remember, warmer water cannot hold as much oxygen as cooler water. Also, the gross oxygen consumption inceases as fish get bigger. For example, (hypothetical numbers) catfish-X uses 5 ml of oxygen per hour, another fish (catfish-Y) is 1/10th of Catfish X's size and uses 2.5 ml per hour. The oxygen consumption/demand is greater for the smaller fish (amount of oxygen consumed per unit body weight) but the gross amount of oxygen being used from the water is higher for larger fish.
