Its summertime in the Buckeye State and of course its hot, hot, hot! As uncomfortable as the sweltering heat is for us, would you believe that in some cases, fish find the soaring temperatures downright lethal?
With Ohios air and water temperatures now averaging above 80 degrees, fish living in shallow waterways across the state could be affected by a condition known as summerkill. Small ponds are particularly susceptible.
If youve ever seen several dead fish floating along the edge of a pond or lake youve probably witnessed a summer fish kill. While not a pleasant sight, fish kills are well-documented, naturally occurring incidents that result from critically low levels of oxygen in water especially during the months of July and August. And, many of the Ohio ponds experiencing this condition are not only shallow, but also feature dense vegetation.
High temperatures and a string of cloudy calm days set the stage for summerkill. First, as you may recall from your days of high school biology, oxygen is a by-product of photosynthesis. For photosynthesis to occur, plants need sunlight. Cloudy days make it difficult for aquatic plants to absorb sunlight. Reduced sunlight means a decline in plant-produced oxygen. Second, warm water is not capable of holding as much oxygen as cooler water. Third, organic matter is constantly in the state of decay at the bottom of ponds, and the very process of decomposition uses up oxygen.
This atmospheric cocktail steadily reduces the overall amount of oxygen in the water, literally leaving fish gasping for their next breath.
So whats a fish to do? Fish swimming in oxygen-depleted waters can be seen at the surface opening and closing their mouths as if gasping for air. Called piping, fish use this as a way to get oxygen as it dissolves from the air into the waters surface. Fish may also seek oxygen in other water sources such as incoming streams or submerged springs.
After a time, however, even piping becomes difficult. Muscles used for swimming require oxygen and the fish tire from trying to stay at the waters surface. As a last resort fish move to the edge of the pond where they rest on the bottom, breathing heavily in an effort to obtain oxygen.
If oxygen does not become available, larger fish will be the first to succumb. Large fish require more oxygen than small fish, which, because of their size, may be able to find isolated areas with slightly higher oxygen levels allowing them to survive.
The only way to stop a summerkill is to add oxygen to the water, not a very practical solution especially on larger bodies of water. Of course, Mother Nature can also intervene in the form of a sunny or windy day or even with a summer storm. Fortunately, summerkills do not occur every year, but when they do, they usually run their course in just a few days.
Pond owners can make a difference by using effective management techniques, including proper shoreline grading to limit the amount aquatic plant growth in near-shore waters.
If you own a pond and have questions about how to manage it, contact your state wildlife district office or call 1-800-WILDLIFE.