COLUMBIA, Mo. – The combination of prolonged high heat and dry weather potentially threatens fish ponds, says a University of Missouri Extension fisheries and wildlife specialist.
“Fish are at risk from high water temperatures, oxygen depletion, increased disease potential and other problems as water levels drop in ponds through lack of runoff and evaporation,” said Bob Pierce.
“Ponds potentially most at risk are those that depend on water from surface runoff within a watershed that may be too small to maintain a pond’s water level, even during years of average rainfall,” he said. “Ponds typically need a surrounding watershed that is about 15 times larger than the area of the pond.”
Two MU Extension publications explain how to monitor your pond and respond to problems. “Managing Fish Ponds During an Extended Drought” (G9401) is available for download at www.extension.missouri.edu/p/G9401. In addition, the MU Extension guide “Pond Dynamics and Water Quality Considerations” (G9476), at www.extension.missouri.edu/p/G9476, provides basic information on pond ecology, water quality and steps you can take to prevent fish kills during the summer months.
Under extended dry conditions, watershed ponds can lose a lot of water to evaporation and seepage, reducing both the oxygen supply and the amount of living space for fish populations. Long stretches of scorching temperatures make the problem worse. “Warmer water can’t hold as much oxygen as cool water,” Pierce said. “A combination of extended dry conditions and higher than normal temperatures like we are having right now can leave ponds with dangerously low levels of dissolved oxygen.”
Fish gulping for air at the surface just after sunrise is an early symptom of low levels of dissolved oxygen. A common way to increase dissolved oxygen is to use a commercial surface aerator — a pump and a nozzle that sprays water into the air. Any technique that mixes water and air can help provide an oxygen refuge for fish. But supplemental aeration is only a remedy for low dissolved oxygen levels, so landowners will also need to address other factors causing the problem, such as an overabundance of decaying aquatic plants and algae.
Refrain from the supplemental feeding of fish during extremely warm weather, Pierce said. Fish will often go “off feed” when water temperatures are around 85 to 90 F, so most of the uneaten feed will sink to the bottom and decompose. The decomposition process can further decrease the amount of available oxygen in the pond.
Falling water levels also leave a pond’s fish with less and less living space. Crowding makes fish more vulnerable to stress and disease. Nutrients and waste products become more concentrated as the pond shrinks, further increasing the risk of oxygen depletion, disease outbreaks, and other problems, he said.
Landowners can reduce the chance of fish kills by keeping livestock out of the pond and avoiding the overuse of fertilizer in the watershed. Wise watershed management and proper design and construction of the pond can lessen the impact of drought, said Pierce.