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UF/IFAS researchers blame cold for fish kills, offer suggestions

GAINESVILLE, Fla. — Cold weather is killing fish in northern and Central Florida counties, according to University of Florida Institute of Food and Agricultural Sciences researchers, who are also offering some solutions.

“In an aquaculture operation, farmers can cover their ponds with a frame covered with plastic, as ornamental fish farmers do in the Tampa area to protect their fish from the cold,” said Charles Cichra, professor of fish ecology and management at the UF/IFAS School of Forest Resources and Conservation.

“If there is a way to create a warm area in a pond, a small proportion of the fish might survive the cold,” Cichra said. “In Lake Alice (in Gainesville), there are small areas that receive warmer ground water via pipes. Some of the fish will find these and survive.  It only takes a few fish to repopulate a pond after a kill. Warmer water, say from a well, could also be pumped into a pond to create a small area of warmer water, but this can be expensive.”

Cichra and his colleagues are getting calls about fish dying northern and Central Florida counties.

Many people have heard about or seen fish dying in Florida ponds, lakes and streams, Cichra said. On Jan. 26, the Florida Fish and Wildlife Conservation Commission said there had been 241 reports of dead fish in Duval, St. Johns and Hillsborough counties alone – potentially involving several thousand fish, and that cold weather killed them.

“When the water or air temperatures fall below a critical level — scientifically termed their ‘lower lethal temperature’ — for a particular species, they will die,” Cichra said. “Humans, for example, can die due to hypothermia, when their body core temperature falls below a critical level. As a result of Florida having a sub-tropical climate and several years of mild winters, quite a few exotic tropical fish species have become established or extended their range further into North Florida.”

Those North Florida waters are colder than those in South Florida, Cichra said. Couple that with the fact that this winter has been chillier than recent ones, and some fish encounter problems, he said.

“This combination of a recent history of mild winters with an unusually cold winter has resulted in large die-offs of tropical fish such as blue tilapia,” Cichra said.

In addition to exotic fish, some native aquatic species are also prone to cold-weather-induced kills, UF/IFAS researchers said. Gizzard and threadfin shad often die during cold weather.

Florida’s largemouth bass can die due to low water temperatures, while the ‘Northern’ largemouth bass survive, Cichra said.  Marine species, such as common snook, have also been dying in north Florida, especially if they are located in shallow areas that experience rapid drops in water temperature.

Even if fish don’t immediately die from cold, they will often become stressed, which can make them more susceptible to future illnesses, such as bacterial and fungal infections, Cichra said. Some of these fish may later die if their illnesses are severe. Even if they don’t die, many may have temporary sores on the exterior parts of their bodies. Read here for more information.

For more information about the fish kills or potential fish kills, contact Cichra at 352-273-3621, or cecichra@ufl.edu.

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By: Brad Buck, 352-294-3303, bradbuck@ufl.edu

The mission of the University of Florida Institute of Food and Agricultural Sciences is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS works to bring science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents. Visit the UF/IFAS web site at ifas.ufl.edu and follow us on social media at @UF_IFAS.

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