LSU
AgCenter Experts Caution Fish Kills Can Result From Storms
Posted:
10/7/05
The recent hurricane-related
weather experienced throughout much of Louisiana can cause
a number of problems for pond owners, including poor water
quality and fish kills from low oxygen or disease, experts
with the LSU AgCenter caution.
In addition, loss
of stocked fish or contamination with wild fish also are likely
in ponds where floodwaters went over the levees.
"Since estimates
of the number of recreational and farm ponds in Louisiana
range from 90,000 to as many as 120,000, problems probably
will be widespread over the next several weeks," said
LSU AgCenter aquaculture specialist Dr. Greg Lutz.
As for fish kills
from low oxygen, the experts say problems with oxygen can
be caused by severe weather in several ways.
" In many
Louisiana ponds, a condition known as stratification occurs
during the summertime," Lutz explained. "Cold, stale
water accumulates on the pond bottom, unable to mix with the
surface."
Lutz said that
layer of water generally contains no oxygen and can build
up naturally toxic compounds like hydrogen sulfide and ammonia.
"But then
when a severe weather disturbance with high winds or heavy
rainfall occurs, this stagnant bottom water is mixed with
the rest of the pond – often resulting in oxygen depletions
and fish kills," he said, adding, "This weather-related
phenomenon is usually referred to as a pond turnover."
Another type of
problem results when prolonged cloudy weather and high turbidity
from wind and rain runoff greatly reduce the natural algae
populations present in ponds.
"These single-celled
plants are the primary source of oxygen in most ponds,"
said LSU AgCenter aquaculture and coastal resources agent
Mark Shirley, explaining why loss of algae is a major issue.
Other problems
with oxygen can result from too much organic matter entering
ponds, either through excessive rain runoff from surrounding
areas or from the decomposition of leaves, sticks and branches
that have been blown in by heavy winds.
"Even when
these processes do not cause oxygen problems directly, the
increased fertility levels can cause excessive algae blooms,
which can eventually lead to fish kills," Shirley said.
Even when turnovers
and low oxygen levels do not kill fish directly, they often
result in physiological stress that can weaken fish’s
immune systems and make them more vulnerable to diseases and
parasites.
"This problem
can be compounded if floodwaters have allowed wild fish –
and the diseases and parasites they may be carrying –
to enter the pond," said Dr. Robert Romaire, who heads
the LSU AgCenter’s Aquaculture Research Station in Baton
Rouge.
Another issue for
pond owners, according to the experts, is that many of them
rely on rainfall and runoff from surrounding areas as their
only sources of water.
"But when
too much water comes at once, many ponds are not properly
constructed to allow for controlled outflows," Lutz said.
"A number of modifications can be made to ponds to better
cope with excessive runoff, including installation of spillways
and overflow pipes, as well as excavating diversion ditches
to channel excess runoff around ponds."
More information
on these problems and tips on how to handle them can be found
in LSU AgCenter’s Publication No. 2573, "Management
of Recreational and Farm Ponds in Louisiana, " which
is available through parish offices of the LSU AgCenter or
online at http://www.lsuagcenter.com.
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