Could someone school me and others possibly, on the ins and outs of d.o.? I have noticed, that in the koi pond in my back yard, after a rain (like last night), all the fish seem to come up shallow, and most will actually hover right at the top. In trying to relate this to bass activity, I was wondering if it had to do with the d.o. level. My pond is very small, about 1/4 of an acre, and only goes 6' deep at the deepest. There are also two waterfalls, so I dought there is an oxygen shortage, however, there is a definite change in their activities after it rains. Connected? Thanks for any info.

Doc is effected by temperature, light and barometric pressure (altitude). Dissolved oxygen decreases as water temperature rises and increases as barometric pressure increases. Oxygen enters the water from plants and wind. Clear water that has good underwater plant life tends to have better oxygen than muddy water. Because of muddy water blocks out the sun plants are unable to produce as much oxygen. When oxygen levels drop by 25% fish become inactive and don't feed as often and move to a new area and at 50% could die from suffocation. The higher the water temperature the more a bass uses oxygen. Fish try to locate the best areas that have the most Doc like the thermocline. Your fish might be up because that is the layer that has the best oxygen. The higher the oxygen content the more active the fish are going to relative to the water temperature.

Very nice explanation, Chris. Better than I could have said it.

The carp in your pond are more likely skimming the surface of nutrients washed into the water from the rain.

Dissolved oxygen (DO) is exactly that; dissolved oxygen within the water, generally measured in milligrams per liter; mg/l

Most fish breath DO in the water and can not breath oxygen directly from the atmosphere. Bass survival limits are ; 3 mg/l to 12 mg/l, with 7 to 9 mg/l being the preferred comfort range.

barometric pressure has a minimal affect on DO, about 0.25 mg/l difference from sea level to 5,000 feet.

Water temperature however affects DO levels; the colder the water the higher the saturation and warmer the lower the saturation levels; 90 degree water, the max DO approaches 3 mg/l. 38 degrees water is about 12 mg/l, the basses survival limits for both DO & temperature.

Wind mixes the upper water column with DO from wave action in lakes and current tumbling the water mixes DO in rivers and streams. Green aquatic plants produce DO via photothynsesis during sunlight periods and consume DO during dark hours. Decaying aquatic plants also consume DO.

Rain drops have zero DO, until mixed by wind and surface turbulence.

WRB

Ah, I think I get it now. Thanks, guys.

Your Welcome