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Spawning stress causes panfish kills in southern Iowa lakes

  • 5/23/2023 3:35:00 PM
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Iowa Department of Natural Resources (DNR) fisheries biologists have investigated recent reports of dead bluegill and crappie in southern Iowa lakes.

These natural fish kills are a common occurrence at a number of lakes each spring during spawning season. There is little danger to the overall population of bluegill or crappie. Iowa lakes can support thousands of panfish per acre of water.

The spawning season is very stressful. A variety of factors can cause this stress, including changes in water temperature, water quality and availability of food. Fish are more vulnerable to predators during spawning, which can add to their stress levels.

“Overcrowding is one of the main causes of spawning stress in bluegills and crappies,” explains Chris Larson, DNR fisheries supervisor. “When too many fish are in a small area, they can become stressed and agitated. This can lead to fights and injuries that can cause stressed fish to become more susceptible to various bacterial or fungal infections.”

If you see dead fish – especially when there are several species or sizes, or when you can see a pollutant present – call the DNR’s 24-hour spill line at 515-725-8694 as soon as possible. Quick reporting can help DNR staff identify the cause of a fish kill and potentially stop a fish kill in progress.