I have had a few calls lately concerning fish dying in ponds. When large numbers of fish show up dead within the period of a day, a fish kill has occurred. Smaller numbers of fish dying over a period of several days indicates a disease-related problem.
Oxygen depletion is the leading cause of fish kills in Oklahoma ponds. Because low-oxygen kills are usually sudden and massive, many pond owners mistakenly jump to the conclusion that a pesticide must be responsible. The following signs point to low oxygen as the cause of a fish kill:
• Fish gulping at the water’s surface.
• Bass die first.
• Large fish die before small fish of the same species.
• Pond water changes color.
• Light scum or a film is visible on the water.
If you see fish gulping at the surface and not too many have died, it may be practical to try saving the rest by aerating the water. This can be done by backing a boat into the water and running the outboard motor with the propeller near the surface to maximize splashing. A pump can be set up to allow water to cascade over boards or a roll of fencing to break it up into as many drops as possible. Some pond owners report success in using a tractor-mounted brush hog to aerate the pond. Aeration should continue at least until fish are no longer at the surface and possibly for as long as several days to allow oxygen levels to recover.
Pesticides do occasionally cause fish kills. Some or all of the following signs can indicate a pesticide fish kill:
• Animals other than fish are dead.
• Small fish die sooner than large ones.
• Fish may be seen swimming convulsively.
• Fish with fins flared out.
Oxygen in ponds comes from two sources — photosynthesis and diffusion from the air. The most important source is photosynthesis, which is the process plants use for manufacturing food. In the presence of sunlight, plants — especially algae — add oxygen to water as a by product of photosynthesis. At night, no oxygen is produced, but respiration of algae, fish and bacteria continues to remove oxygen from the water. Most of the time there is a desirable balance between how much oxygen is produced and how much is used, but under some conditions the balance can be upset and the oxygen concentration becomes low enough to stress or kill fish.
The amount of oxygen in pond water can vary considerably from pond to pond and from hour to hour. Typically, however, oxygen concentrations are lowest at dawn and highest during late afternoon.
The most important factor is water temperature. As temperature increases, water holds less oxygen. Most low-oxygen problems occur from June through September. The reasons for this are:
• Water can hold less oxygen as it becomes warmer.
• Respiration rates of both plants and animals increase with the warmer water, so more oxygen is used.
• Summer’s still, hazy or cloudy days may reduce the amount of oxygen produced.
• Large amounts of feed given to fish at this time of year result in large quantities of fish waste which create a higher demand for oxygen.
The most common oxygen problem occurs when consumption by respiration exceeds the amount of oxygen produced through photosynthesis and diffusion from the air. Algae grow in large quantities as a result of heavy fish feeding or other nutrients coming into the pond. As the quantity of algae increases, it accumulates closer and closer to the surface to gather sunlight and increasingly shades the lower depths. As a result, most of the oxygen is produced near the surface, leaving a large volume of water below the first two-to-four feet deficient in oxygen production. Eventually, oxygen produced during the day is less than the demand for oxygen during the night, resulting in possible death or undesirable stress on fish.
If you have questions concerning this topic or related topics, please contact the OSU Extension Center at 273-7683, stop by the office, or visit our Web site at http://countyext.okstate.edu/pottawatomie/.
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I have had a few calls lately concerning fish dying in ponds. When large numbers of fish show up dead within the period of a day, a fish kill has occurred. Smaller numbers of fish dying over a period of several days indicates a disease-related problem.
Oxygen depletion is the leading cause of fish kills in Oklahoma ponds. Because low-oxygen kills are usually sudden and massive, many pond owners mistakenly jump to the conclusion that a pesticide must be responsible. The following signs point to low oxygen as the cause of a fish kill:
• Fish gulping at the water’s surface.
• Bass die first.
• Large fish die before small fish of the same species.
• Pond water changes color.
• Light scum or a film is visible on the water.
If you see fish gulping at the surface and not too many have died, it may be practical to try saving the rest by aerating the water. This can be done by backing a boat into the water and running the outboard motor with the propeller near the surface to maximize splashing. A pump can be set up to allow water to cascade over boards or a roll of fencing to break it up into as many drops as possible. Some pond owners report success in using a tractor-mounted brush hog to aerate the pond. Aeration should continue at least until fish are no longer at the surface and possibly for as long as several days to allow oxygen levels to recover.
Pesticides do occasionally cause fish kills. Some or all of the following signs can indicate a pesticide fish kill:
• Animals other than fish are dead.
• Small fish die sooner than large ones.
• Fish may be seen swimming convulsively.
• Fish with fins flared out.
Oxygen in ponds comes from two sources — photosynthesis and diffusion from the air. The most important source is photosynthesis, which is the process plants use for manufacturing food. In the presence of sunlight, plants — especially algae — add oxygen to water as a by product of photosynthesis. At night, no oxygen is produced, but respiration of algae, fish and bacteria continues to remove oxygen from the water. Most of the time there is a desirable balance between how much oxygen is produced and how much is used, but under some conditions the balance can be upset and the oxygen concentration becomes low enough to stress or kill fish.
The amount of oxygen in pond water can vary considerably from pond to pond and from hour to hour. Typically, however, oxygen concentrations are lowest at dawn and highest during late afternoon.
The most important factor is water temperature. As temperature increases, water holds less oxygen. Most low-oxygen problems occur from June through September. The reasons for this are:
• Water can hold less oxygen as it becomes warmer.
• Respiration rates of both plants and animals increase with the warmer water, so more oxygen is used.
• Summer’s still, hazy or cloudy days may reduce the amount of oxygen produced.
• Large amounts of feed given to fish at this time of year result in large quantities of fish waste which create a higher demand for oxygen.
The most common oxygen problem occurs when consumption by respiration exceeds the amount of oxygen produced through photosynthesis and diffusion from the air. Algae grow in large quantities as a result of heavy fish feeding or other nutrients coming into the pond. As the quantity of algae increases, it accumulates closer and closer to the surface to gather sunlight and increasingly shades the lower depths. As a result, most of the oxygen is produced near the surface, leaving a large volume of water below the first two-to-four feet deficient in oxygen production. Eventually, oxygen produced during the day is less than the demand for oxygen during the night, resulting in possible death or undesirable stress on fish.
If you have questions concerning this topic or related topics, please contact the OSU Extension Center at 273-7683, stop by the office, or visit our Web site at http://countyext.okstate.edu/pottawatomie/.
