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Fish kills can result from storms

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 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 Robert Romaire, who heads the LSU AgCenter's Aquaculture Research Station in Baton Rouge, La.

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.

Tom Merrill is News Editor for LSU AgCenter Communications.

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