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Fish Kills and Pond Management Tips for Fish Kill Prevention

By Garrett Lee

Fish dying in your pond is a natural occurrence. Losing all of the fish in your pond (known as a fish kill) however is a major problem. The first step in repairing your pond is to remove the dead fish and determine what caused your fish to die. Fish kills are often caused by three main factors: oxygen depletion, water chemistry imbalances or polluted water.

The Number One Cause of Fish Kills is Low Oxygen Levels

The number one cause of fish kills is low oxygen levels in the water. Fish need oxygen to breathe the same as we do. They rely on fresh oxygen being introduced into the water. Oxygen is removed from water by fish respiration, bacteria that consume decaying organic matter, and aquatic plants during the respiration portion of the photosynthesis cycle. Plants consume oxygen from water when there is a lack of sunlight.  Multiple, consecutive overcast days with little wind can spell disaster for your fish.

It is especially important to monitor oxygen levels during the summer months. Higher water temperatures, pond evaporation and elevated nutrient levels all come together to threaten your pond. Fish gasping at the surface is a quick indicator that you have an oxygen problem. The most important time to observe this is early in the morning when oxygen levels will be the lowest. Aerators and fountains are both ways to add more oxygen to your pond or lake to ensure appropriate levels at all times. Learn more about aeration.

Poor Water Chemistry is Another Cause of Fish Kills

Water chemistry is another factor to take into consideration. A water sample from your pond needs to be analyzed to determine if the chemistry of the water is causing your fish to die. Factors such as pH, alkalinity, and hardness are some of the first tests that need to be ran. Basic water testing kits have individual tests for these factors. If you choose to have someone else perform these tests, take a sample to your county extension agent or a pond management company. We also offer pond management services here at Pond King. Once you have the results of the analysis, a determination can be made as to if these influences are causing your problem.

Pollutants Can Also Be Responsible for Your Fish Dying

Pollutants can be introduced into your pond causing another form of fish kill. They can come in many forms, such as gas or oil to pesticides that are applied to the land near your pond. Point source contaminants are pollutants that are directly introduced into your pond. Non-point source contaminants are pollutants that are introduced from miles away by surface runoff or other contaminated water sources.

An in-depth water quality analysis needs to be performed To determine if pollutants have caused your fish kill. Contact your county extension agent or a pond management company and they will refer you to a water testing company that can perform these tests.

Modify Your Pond Management Strategy to Prevent Fish Kills

When you come to the conclusion of what caused your fish to die a modified management strategy can be implemented to prevent another occurrence. Reference Table 1. below for possible alterations to your management practices once you have determined the cause of the fish kill. For any other questions you might have about the conditions of your pond feel free to contact me at garrett@pondking.com

Table showing possible fish kill cause and pond management prevention
Table 1. Management Alterations After Fish Kills

Tags: Fish and Fishing, Pond Management

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