Low Oxygen

You don’t need me to tell you it is hot outside. The fish in your pond or lake know it too. As we move into these warmer months, your water temperatures will no doubt be on the rise. With the rise in water temperatures, the amount of oxygen that can be dissolved into the water (so your fish can breathe) is reduced. Fish kills are common at this time of year, and the hotter the temperature the greater the risk.

Unfortunately, fish kills are a part of pond management. Most at this time of the year can be traced back to low oxygen. There are several steps that can be taken to reduce the risk or minimize the loss of a fish kill. The first is one you are probably already doing and that is watching your fish. The more you watch them the more likely you will notice behavior that is out of the ordinary. The best time to evaluate fish in a pond is during feeding. That being said, the time of day you feed your fish is important in managing low oxygen events. Try not to feed before the sun has been up for a couple of hours. This will allow the oxygen producers (algae) in the pond to start the photosynthesis process and the dissolved oxygen levels will be on the rise. Try not to feed too late in the evening. A full fish requires much more oxygen than an empty fish. The best time to me is around 9 to 10 a.m. By then the sun has been up for long enough, and it has not yet arrived at the heat of the day. The fish will have plenty of time to metabolize the feed they have eaten before the sun goes down and photosynthesis stops. If you are ever concerned you are having a low oxygen event, do not feed the fish. Better to be safe on this one, and fish can go quite a while without feed in most recreational ponds. If you see your fish on the surface gulping air, it is a good indication that the oxygen level in the pond is low. You will typically see this first thing in the morning right around sunrise.

An additional measure to manage against low oxygen fish kills is the installation of an aerator. An aerator or even a fountain will help the fish by providing an area within the pond that they can go to during low oxygen events. If you have an aerator make sure that you run it at night when you are having a dissolved oxygen problem. For new ponds, aeration is an excellent addition to the plans. Furthermore, make sure you do not overstock ponds (new or existing).

If you have experienced a fish kill and suspect oxygen, some things to consider include the size of the fish that died. Typically, larger fish die first in low oxygen events. Did the pond change colors rapidly (overnight)? Have you seen the fish on the surface gulping air/water? Each of these are signs of a low oxygen related problem in a pond or lake.

For additional questions or information, contact P.J. Waters, Auburn University Marine Extension and Research Center, 438-5690.

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