How to Avoid a Devastating Fish Kill

August 15th, 2014

Fish-Kill1The last thing a pond owner, homeowner, or lake manager wants to find is dead fish in their lake or pond. Fish kills can be disturbing and stressful for all parties involved, and understanding how and why they occur will aid in preventing them. Fish kills can typically be attributed to natural causes, and recognizing them early is essential.

Dissolved oxygen is essential in lakes and ponds for fish and other aquatic animals to breathe. Pond algae and other aquatic plants produce oxygen during photosynthesis, but during cloudy days and evenings, little to no oxygen is produced. When fish and other species are utilizing more oxygen than is available, the dissolved oxygen can drop to dangerous levels. Fish can start to become stressed and sometimes gulp at the surface when dissolved oxygen drops lower than 5 mg/L, with more sensitive fish dying from lack of oxygen.

Low dissolved oxygen issues will typically be encountered in the summer because warmer water holds less oxygen than colder water. Aeration will aid in bringing oxygen-rich colder water to the surface and promote mixing of the different temperature layers within the lake or pond to provide oxygen throughout the water column.

pond aeration system can be a valuable tool in preventing fish kills, but cannot eliminate the potential for them to occur. During the spring and summer, thunderstorms can create pond turnover, where oxygen-poor bottom water and organic material is brought to the surface. This situation can cause a rapid oxygen crash and a sudden and significant fish kill could occur.

While algae can be beneficial in providing oxygen for fish, excessive algae growth and certain algae species can have negative effects on animal health. Excessive algae blooms provide a large amount of organic matter for microbes and bacteria to consume. The oxygen produced by these blooms can be rapidly utilized by bacteria and microbes as they feed and respire. Having an algae management plan can help control algae blooms before any issues arise.

Establishing a management plan for your lake or pond can aid in algae control and work toward preventing some of these problems from occurring. Fish kills due to spills or toxicity issues are rare and natural factors can usually be isolated as the cause. Awareness of these natural factors, aeration, and a lake management plan are important in lowering the chances of a fish kill in your lake or pond.

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