Oxygen Problems In Ponds
Galen Jons, Fisheries Biologist
We often receive calls from pondowners complaining about fish kills in their ponds. Occasionally these kills are caused by things such as chemicals washing into a pond after a heavy rain, but usually the culprit is simply a lack of oxygen in the pond water. Just like people, fish need oxygen to survive. If there isn't enough dissolved oxygen in the water, they will go belly up.
Most oxygen problems occur during the warmer months because warm water holds less oxygen than cool water. Additionally, fish are moving and feeding more and require more oxygen. Algae and other microscopic plants usually grow best during the warm, sunny summer months. While this plant life adds oxygen to the water as long as the sun shines, it will use up oxygen during the night, or on cloudy days when little sunlight reaches the pond.
Ponds that contain a lot of fish, or a lot of big fish, are more subject to oxygen problems. Also, ponds that are fertilized or where the fish are fed (such as catfish ponds) are also prone to oxygen problems.
How do you know if you might have oxygen problems?
Since plants use oxygen during the night, it makes sense that oxygen levels will be lowest just before sunrise. Visit your pond at daybreak and look for signs of fish stressed by low oxygen. This is usually indicated by fish swimming near the surface and possibly even trying to gulp air at the water's surface. If it's going to be a sunny or windy day, you may be fine. If it's going to be a cloudy day, you may want to aerate the pond.
Aerating the pond can be expensive. However, some pond owners aerate their ponds throughout the summer just for good insurance, especially in ponds containing lots of fish. Aerating usually only needs to be done from about 5am through 10am on sunny days, and usually all day on cloudy days. It also usually needs to be done only from June through September, when water temperatures are warmer.
When selecting an aerator, look for one that injects air along the pond bottom, or, if you like the fountain type, look for one that breaks the water up into droplets as small as possible. A fine spray is desirable, as it greatly increases the surface area of the water, enhancing its ability to absorb oxygen from the atmosphere before falling back into the pond.
For those who don't have a lot of fish in their pond and don't want to go to a lot of expense, there are a few options. A water pump placed at the pond's edge can be used to spray water into the air so that it breaks up into small droplets as it falls back into the pond. An outboard motor on a boat parked on the shoreline can also be used to stir up the water. Some pondowners actually have home-made paddle wheels manufactured from old car/truck running gear that are driven off a tractor PTO. These may be expensive initially, depending if you already have the materials, but are pretty efficient at mixing the water up quickly.
Texas Parks and Wildlife Dept.
5325 N. 3rd
Abilene, TX 79603
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