During Winter, Fish Health in Ponds Depends on Available Sunlight
By:Will Hehemann, writer/editor
UAPB School of Agriculture, Fisheries and Human Sciences
During winter months, farm pond owners in Arkansas may wonder about the risks posed to their fish populations in the event of icy weather, Larry W. Dorman, Extension aquaculture specialist at the University of Arkansas at Pine Bluff, said.
“Ice coverings on lakes and ponds can lead to problems,” he said. “But farm ponds in southern regions are usually spared any major fish losses thanks to mild winters.”
Dorman said the health of a pond during icy weather depends on the ability of sunlight to travel through the pond’s frozen surface. Phytoplankton, the microscopic plants that live in a body of water, depend on sunlight to survive. If sunlight does not penetrate the surface of a pond for an extended amount of time, the plankton die.
Dead plankton cause a chemical reaction that removes oxygen from the water and can eventually cause oxygen depletion. This process may result in a pond full of dead fish, a phenomenon referred to as a “winterkill.”
Clear ice does not restrict sunlight from entering a pond, Dorman said. Even a layer of clear ice with a thickness of two feet has virtually no effect on the utilization of light by phytoplankton. On the other hand, surface ice that is opaque, contains a large number of air bubbles or covered in snow vastly reduces the amount of light penetration in a pond.
Winterkill is seen annually in ponds in northern states, most frequently in shallow, fertile ponds. Therefore, biologists commonly recommend that ponds in these areas should be constructed at a depth of 10 or more feet and should not be fertilized.
“Overall, Arkansan pond owners should not be concerned about the possibility of fish kills due to freezing,” Dorman said. “However, unusually long cold spells occur from time to time. There is a simple step landowners can take to help ensure their pond’s ecosystem remains healthy through a long freeze.”
If a pond has been frozen over for a period of three weeks or more, part of the icy surface should be broken in order to re-oxygenate the pond, he said. Landowners can pierce the ice cover by melting a portion with hot water or using an axe, pick or chainsaw to create a hole that vents out excess carbon dioxide and allows oxygen in.
“For the most part, Arkansas farm pond owners should not be concerned about freezing temperatures affecting their fish populations,” Dorman said. “In the event of lingering low temperatures, however, it is always best to be prepared to take the simple measures necessary to help ensure a pond’s health during an extended freeze.”