What Causes Fish to Die in a Pond?

Like any living creature, pond fish require specific conditions to survive. Fish in a pond can't escape poor water conditions or overcrowding. Correct pond design is the first step in ensuring the health of your fish. A fish pond owner should address the issue of correct water depth while the pond is still in its design stage. If you maintain your pond correctly, your fish will grow and thrive.

  1. Low Oxygen Levels

    • Pond fish die if their water has low levels of oxygen. This happens by overstocking of fish or a shallow pond that warms up too quickly; warm water holds less oxygen than cooler water. Beneficial filter bacteria will also compete with fish for the available oxygen and in poorly managed ponds both bacteria colonies and fish will suffer.

    Disease

    • Water chemistry, temperature and nutrition affect the health of pond fish. Poor living conditions lower the immune system of a pond fish. The fish experiences stress, which predisposes it to disease. Whitespot is a common and potentially lethal disease. Treat this single-celled protozoan as soon as possible to prevent death of all fish in the pond.

    Toxic Water Conditions

    • The metabolic waste of pond fish produces ammonia. This product is toxic and will quickly kill pond fish. In a well-maintained pond with a correctly sized filter, the beneficial bacteria that coat the biological filter material break ammonia down into less harmful substances. Nitrite is produced which is the least harmful. In ponds without biological filtration, or where the filter is not large enough to process the fish waste, these toxic chemicals build up and the fish will die.

    Low-Water Temperatures

    • Water temperature governs the body temperature of pond fish. The metabolism of fish slows down considerably during very cold periods and they eat less, if anything. Their immune system also decreases during these periods. Pathogens or disease-producing organisms in the water attack the fish when the water temperature rises, because their immune system is not functioning optimally. Sudden changes in water temperature also stress pond fish and predispose them to illness.