County Extension Agent
Starting at this time every year we start receiving calls from pond owners concerned about losing fish. The number one factor attributing to this is oxygen depletion. Owners need to be aware of the causes, signs and corrective measures to help lower your likelihood of experiencing oxygen depletion.
There are many factors or combination of factors that could lead to or cause oxygen depletion.† Regardless of the size of your pond, no pond is exempt from this problem.† However, itís usually the smaller ponds with high fish populations that show signs first.† Oxygen levels are at their lowest at sunrise.† Therefore, if you feel you may be susceptible to oxygen depletion its best to look for fish coming to the surface and swimming sluggishly early in the morning.
Most oxygen depletion occurs in warm weather, the summer months.† This is because warm water holds less oxygen than cold water and a fishís metabolism rate is also faster in warmer conditions, thus resulting in the fish needing more oxygen when the oxygen supply is lower.
Another cause could be exceeding the carrying capacity of the pond.† Typically our ponds reach their lowest levels in the hot summer months, but our fish number remains the same.† This results in an increase of pounds of fish per surface acre of water.† This is seldom a problem but has been noted in a few cases.
Improper aquatic weed control is a large factor in fish die-off.† Most pond owners donít think about aquatic weed control until the weeds are mature and pose a problem.† Treated aquatic weeds sink to the bottom and decay and the decomposition process removes oxygen from the pond.† Remember itís always better to treat ponds in 1/4 to 1/8 sections early in the growing season (April or May) a week to 10 days apart.
Unfortunately most ponds suffer from oxygen depletion for a few days before it is noticed by the owner. However, the problem can be corrected if found early and the owner acts quickly in correcting the problem.† Learn to watch for signs of oxygen depletion. If oxygen levels in the pond need to be quickly increased, the fastest way is to bring pond water into contact with air.† The best way to do this is by pulling water from the pond and shooting or spraying it back into the pond.† Outboard motors also work if used in a fixed position.† The idea is to get a circulation pattern to move the oxygen throughout the pond.† Remember these are only temporary corrective measures if the cause or causes of the oxygen depletion are not corrected.