Remedial measures for oxygen depletions in ponds can be any method that adds sufficient oxygen to the pond water to prevent or minimize a fish kill. A water pump can be used to pump fresh water into the pond, or the water in the pond can be sprayed into the air and allowed to fall back into the pond. This will oxygenate the water, however, it is important that water that is sprayed is water taken from near the surface and not stagnant bottom water. Any device that agitates and aerates the water sufficiently can be of value. Do no use well water as a source for pumping fresh water into the pond, as it can be very low in oxygen.
Pesticides cause a number of fish kills in ponds throughout Alabama each year. Convulsive, erratic swimming and lethargy are symptomatic of pesticide toxicity. If an organo-phosphate insecticide is the cause, the pectoral fins of the fish will be reversed. The pectoral fins of a healthy fish point toward the tails, but the pectoral fins of a fish poisoned by insecticide curl up and point toward the head. Generally, the small fish will be killed first and eventually all sizes of fish may die.
Fish ponds should not be built in areas adjacent to crops that are likely to be treated with pesticides toxic to fish. Diversion ditches should be dug around the pond to prevent toxic runoff water from entering it.
If a pesticide-caused fish kill is suspected, a one-gallon water sample should be taken as soon as possible in a clean glass container. A piece of aluminum foil should be placed over the mouth of the container under the lid, and the container should be labeled with the collector’s name and address. The name of any herbicide or pesticide recently used in the watershed should also be included. The sample should be packed in a styrofoam container to prevent breakage, iced down and shipped to: The Alabama Pesticide Reside Laboratory, 1081 S. Donahue Drive, Auburn, Alabama 36832. Shipment by bus is preferred for such a large heavy package. The label should contain the notation “Urgent--Please phone 844-4705 on arrival.” The laboratory will test the sample and send the results to the pond owner.
Other major causes of fish kills in ponds are parasites and disease. Fish killed or weakened by parasites and/or disease may show visible external signs, such as lesions, hemorrhages or changes in pigmentation. The fish may be sluggish or swimming erratically.
A fish kill caused by parasites or disease will extend over a longer period of time, compared to a kill caused by oxygen depletion, when large numbers of fish are killed within a few hours. The fish kill may occur over a period of several days or even several weeks, with a few fish dying each day. The number of dead fish gradually increases until it peaks, and then decreases as the parasite or disease runs its course.
Diagnosis of a suspected parasite or disease kill can be made by the Parasite and Disease Laboratory at Auburn University’s Department of Fisheries and Allied Aquaculture. Contact the lab at 334-844-4786 for information concerning this service. There is a charge for this service. The decision about using this service should also include questions of how the diagnosis will be used. The treatments for many diseases are not worth the effort and expense of the pond owner. The pond owner often decides to let the disease run its course.
Swarming of the winged form of the fire ant in later winter or early spring has caused many fish kills. As the swarming ants fall into a pond, bluegills gorge themselves on the ants. If enough ants are eaten, the fish will die, but the majority of fish feeding on the ants will become ill and recover without lasting effects. Fire ant-caused fish kills do not present a serious problem by significantly reducing the fish population. If a fire ant kill is suspected, examination of the fish’s stomach will confirm the problem.
If a fish kills occurs in your pond, contact your district fisheries biologist for advice and possible assistance. The telephone number for your district fisheries biologist is available from the Wildlife & Freshwater Fisheries Division offices by calling (334) 242-3471 or by finding the information at our Web site at http://www.dcnr.state.al.us/agfd.
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