In the News - August 2008
Are the fish in your pond on the ‘bucket list?’
HOT SPRINGS, Ark. - Some pond owners ponder why many fish in their ponds have
"kicked the bucket," said Jimmy Driggers, Garland County extension agent staff
chair with the University of Arkansas Division of Agriculture
Fish killed in private fish ponds by infectious diseases, pesticides and
other accidental chemical contamination is extremely rare. But sudden fish
die-offs are usually caused by oxygen problems in a pond and can be prevented.
"The first sign of low oxygen that most pond owners see is the fish at the
pond surface, piping," Driggers said. Piping refers to fish with their mouths at
the surface sucking surface water, which has higher oxygen content.
Fish that become startled and submerge after being approached can probably be
saved, if aeration is supplied soon enough. Fish that remain at the surface or
lie listlessly in the shallows are close to death, he said.
The common cause of low oxygen within a pond is the sudden mixing of a pond,
called "turnover." This happens in many different sized and shaped ponds, but
deep and sheltered ponds are the ones particularly affected.
Driggers said, hot, still days result in ponds developing temperature layers.
The thin upper layer of water is hotter and contains the microscopic plants that
produce oxygen. The hot water is lighter and floats on top of the cool deeper
water that is not directly exposed to the sun. The cooler bottom water is cut
off from the surface by the upper layer and, over time, becomes low in oxygen.
Leaves and other organic matter in the pond bottom also decrease the supply of
dissolved oxygen as they decompose. Strong winds or rain, after a period of
still weather, can lead to a turnover, where the layers mix.
"The overall mixture can be low in oxygen, especially in ponds that have a
large percentage of deep water," he said.
Oxygen problems are easy to recognize even without an oxygen test kit or
meter, and a potential problem can be detected within a pond if there is a
sudden change in the pond appearance, such as color change, or if the pond has a
strong "rotten egg" smell, which is the result of the release of hydrogen
sulfide gas from the pond-bottom mud during turnover. Hydrogen sulfide is toxic
to fish.
Early detection of oxygen problems is critical, Driggers said. Keep a close
eye on a pond, especially in turnover weather conditions, such as a storm after
hot, still weather. Most fish die within a few hours in water with less than 1˝
ppm of dissolved oxygen. Typically, big fish die before the smaller ones, and
game species such as bass die more quickly than bullheads or carp.
He said, "A cold front with wind and rain may move through in the evening
causing a turnover. By morning fish may be dead."
To have a healthy, oxygenated pond and guard against turnovers, choose and
use a pond aerator. There are fountain-type aerators (water fountains), which
are decorative, and diffused aeration systems. Fountains splash the surface of a
pond, while diffused aeration is when the air diffuser lays on the pond bottom;
this is the best way to go with deep ponds because total pond aeration can be
achieved from the bottom to the top of pond regardless of depth. Oxygen
disperses throughout the pond.
For more information about pond health, pond turnovers or pond aeration
systems, please contact your county extension agent or visit
www.uaex.edu. The Cooperative Extension Service is part of the U of A
Division of Agriculture.
August 8, 2008
Edited by Rhonda Conner
Media Contact: Lamar James
Extension Communications Specialist
U of A Division of Agriculture
Cooperative Extension Service
(501) 671-2187 or (501) 753-0207
ljames@uaex.edu
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