News Releases

Cold weather may lead to fish kills

News Release

Thursday, December 09, 2010

Media contact: Carli Segelson, 727-896-8626

As temperatures drop in Florida, the number of cold-related fish kills is likely to increase. Chilly winter temperatures can lead to fish die-offs in Florida's marine habitats, rivers and lakes.

The good news is that these events are natural occurrences and typically do not cause permanent damage to the ecosystem or to fish populations. In some cases they are even beneficial, in that they help limit the spread of invasive, exotic species.

Fish kills are often caused by sudden temperature fluctuations or by extended periods of extreme temperatures. Such kills can occur any time of the year in Florida, but they are most common in winter, when air temperatures drop. Although water stays relatively warm for awhile after the air cools, extended cold snaps can cause water temperatures in inland water bodies and estuaries to drop. The cold may kill fish outright by cold stress or weaken them so that they are more susceptible to disease. Another phenomenon, called lake-turnover, may occur when suddenly cooled surface water sinks and mixes with deeper, oxygen-poor water. This can cause fish to suffocate, often leading them to gulp at the surface before they die.

Warm-water species, including popular game fish like snook, are particularly vulnerable to cold temperatures. Exotic species such as butterfly peacock bass, tilapia, and sucker-mouth catfish are also especially susceptible to cold weather.

Fish affected by the cold may appear lethargic and may be seen at the surface where the water may be warmer from the sun. All recreational regulations still apply to fish impacted by the cold temperatures, even if they appear to be dead or dying.

It is important for Florida Fish and Wildlife Conservation Commission (FWC) scientists to keep track of the location and extent of fish kills in natural lakes and estuaries, to see if there are problems developing in an ecosystem that might require investigation or restorative measures. Although it is not necessary to report fish kills in private ponds, FWC scientists can assist the public by providing information about cold-weather fish kills in these water bodies.