I have a stainless steel tank that is maybe 400 gallons full that I have about 300 gallons in. I have two submersable pumps going (about 200 gph at 4.5' head). I'm not going to feed them so the water will stay clean. I know I can keep them alive for a while. I just don't know how beat up they will be.
The pond with electicity is the one with feed trained largemouth. They are more precious than my cats so I am keeping the catfish low in that pond.
Plants in the water make oxygen during the day and use a little at night, so even if the plankton doesn't die off, it will lower the oxygen. I'm always surprised when the experts don't mention cloud cover when talking about fish kills. I'm not an expert but I do know that 100% of my fish kills are during cloudy spells. The reason may be because I have too many fish and too many plants and plankton due to cow patties but the catalyst is cloud cover.