We’ve received several inquiries regarding the recent bullhead die-off at North Twin Lake. Our Fisheries Biologist, Ben Wallace, investigated the situation and here’s what we know:
The bullhead die-off is most likely due to spawning-related stress. This type of fish kill is usually straightforward to diagnose. It’s a single species event involving adult bullheads, occurring shortly after their spawning period. During spawning, bullheads expend a lot of energy building, maintaining, and protecting their nests, which weakens their immune systems and makes them more susceptible to disease. The high density of the bullhead population also increases competition and the spread of disease. However, none of the common fish diseases are known to transmit to humans or other warm-blooded animals.
Fish observed with roughed up tails and fins, some with secondary fungal infections, corroborate spawning-related stress. We have no reason to believe pollutants or toxicants caused this event, as more sensitive species would also have been affected if toxins were present.
This natural phenomenon is common among panfish species and is nature’s way of keeping populations in check. We expect this event to taper off soon as we move past the bullhead spawning period. The impact on the bullhead population remains to be seen, but it has certainly thinned out the numbers.
For more information, you can contact:
Ben Wallace
Fisheries Biologist
Black Hawk Fish Management District
Iowa Department of Natural Resources
Phone: 712-657-2638
Email: [email protected]
