This is probably going to sound like a stupid question, but.... Do all fish need oxygen bubbled into the water? Are there any that can just come to the top and suck it out of the air? And if there are such fish, what happens to the water without oxygen being bubbled through it? Does it get yucky? I know knothing about fish... NOTHING. I never even had a goldfish or a guppy when I was a kid. Sue
Sue, I am not Joel but I can answer in layman terms! It depends on a few variables, such as size of fish, fish type (activity levels) and the stocking rate of the fish. Gold fish in ponds don't need air bubbled through water as a ceratin amount of air/water exchange happens on the surface of the water naturally. But when ponds get covered in weeds that area decreases so then does the amount of oxygen in the water. More exchange occurs when the surface is disturbed, so little fountains or trickling "waterfalls" can aide in the exchange rate. When you are having higher densities for production or have warmer temperatures for water (like in tropical tanks), you need to increase the oxygen artificially.
Yeah, rain hitting the surface of a pond or tank or whatever will cause some oxygenation. A certain coverage of weeds will actually also oxygenate the water too. It is when their is more plant material decaying anaerobically than there is oxygen being produced by the plants that you get an oxygen deficiency. I think some fish are more tolerant of low oxygen conditions than others. Catfish, and I believe Tilapia are more hardy in this sense than say, Silver Perch or Bass.