Stocked Fish Ponds More Susceptible to Oxygen Depletion During Summer Months

Well it has become obvious that summer is here and here to stay.  After the last couple of weeks with temperatures above normal, landowners should watch for oxygen depletion in stock ponds as we enter the dog days of summer.  Last week I came across an article written by Dr. Billy Higginbotham, AgriLife Extension Service, Wildlife and Fisheries Specialist discussing landowners with stocked fish ponds should be aware of possible problems with oxygen depletion as hot, still days become more prevalent.

The summer months, between June and September, when the outside air is increasingly hot and pond water temperatures climb, is the time of year when oxygen depletions occur most for a variety of reasons.   Improper aquatic weed control, too many pounds of fish and the weather all contribute.

Typical ponds can sustain 1,000 pounds of fish per surface acre through summer months. When the environment is optimized and the pond owner stocks heavily, especially channel and blue catfish, and feeds heavily with floating fish rations, the density level can be easily met and exceeded.

Oxygen production via photosynthesis can slow or stop from several hot, still, cloudy days and fish continue to use oxygen until it falls below 3 parts per million gallons which stresses fish. Fish will begin swimming to the surface to try to obtain enough oxygen to survive at the air-water interface.

It is best to check the pond at daybreak when oxygen levels are at their lowest daily levels. The pond owner should act quickly if fish are surfacing for air.  Larger fish are affected by low oxygen levels more than smaller fish.  It’s almost as if they are gasping for air at the air-water interface.  That’s a clear sign of oxygen depletion and the pond owner should act quickly to avoid a complete die-off of their fish.

Pond owners can produce more oxygen for fish in various ways.  Backing a boat engine into the pond and circulating the water is one way to create more oxygen.  Pond owners can also place a water pump in a shallow portion of the pond and spray water along the surface to circulate water along the air-water interface. 

Once oxygen levels are restored, pond owners should investigate the pond conditions that contributed to the depletion.  Thinning fish populations to reduce the pounds of fish the pond supports going into the mid-summer months when hot, still cloudy days are prevalent. 

Controlling aquatic vegetation can also contribute to oxygen depletion.  Oxygen is removed from water as plant tissue decomposes, which can create a scenario where a die off might occur.  Weed control efforts should be done gradually, about 15-20 percent of the vegetation at a time and with a week break between treatments.  An aeration system is a good investment for landowners to avoid problems or prevent future problems.

Remember to watch very carefully as we enter these still, cloudy, and hot days of summer.  Also, be mindful of oxygen depletion and the possibility of losing fish populations.