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POND OWNERS: BE ALERT FOR SUMMER
FISH KILLS
Low oxygen content in water can be
a prescription for disaster
July 28, 2006 - PRATT -- Everyone who has
a recreational farm pond enjoys the opportunity to step outside
and catch fish. However, nothing can be more disheartening than
to carefully nurture a pond only to discover a fish kill on a
hot summer morning. The July/August 2006 issue of Kansas Wildlife
& Parks magazine features an article by Pratt Fish Hatchery
manager Mark Kumberg addressing this issue.
To prevent fish kills, a pond or lake must have
one element to support fish and other higher organisms -- oxygen.
Oxygen depletion is the most common cause of fish kills, and
low oxygen occurs most often during periods of calm, cloudy,
hot weather.
Most dissolved oxygen in water comes from the atmosphere
on windy days and as a byproduct of aquatic plant photosynthesis.
Less sunlight penetrates deeper water, reducing deeper water
vegetation, thus reducing oxygen content at deeper strata.
Dissolved oxygen levels can also be affected by
temperature. Colder water holds oxygen better, and very warm
water easily loses oxygen. Atmospheric pressure is also a factor.
Oxygen solubility increase as atmospheric pressure rises.
Most fish kills occur in the early morning before
the sun comes up, when dissolved oxygen levels are lowest, and,
unfortunately, larger fish are usually the first to be affected.
Ponds or lakes with large amounts of algae or phytoplankton can
have high oxygen during the day, but at night, these plants use
up oxygen.
Herbicides or algaecides can help control aquatic
vegetation and reduce the chances of a fish kill. However, this
must be done carefully to prevent rapid decomposition and further
oxygen depletion. Other ways to prevent oxygen depletion include
pumping or flowing water into a pond, preventing runoff that
adds nutrients to a pond, using a commercial aerator, reducing
feed amounts if artificial feeding is used, and maintaining the
proper fish density for the size of the pond.
For more information on pond management, contact
the Kansas Department of Wildlife and Parks at 620-672-5911 or
visit the department
website, to view their pond management page.
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