Removal of Unwanted and Overpopulated Species of Fish is part three of seven in the Management of Recreational Fish Ponds series.
Fish populations in poorly managed ponds usually become out of balance and may become contaminated with unwanted fish species. Typically, Alabama ponds become crowded with small or stunted bass or bream populations or become populated with species like green sunfish, bullhead catfish, shiners, or other unwanted species. The best management option in these situations may be to destroy all fish in the pond and start over but have your pond checked by a qualified fisheries biologist first. Removing or killing the fish population usually is much easier and less expensive if the pond can be drained dry or partially drained and the fish concentrated. Fish will survive in very small pools or puddles away from the main body of water. To get a complete kill you must treat all puddles, even those in the watershed, no matter how small!
Rotenone is a registered aquatic chemical that is used to kill fish. In Alabama, rotenone for pond renovation can be purchased from most farm supply or feed-and-seed stores by anyone with a pesticide applicator permit. Rotenone has been classified as a RESTRICTED USE pesticide.
Rotenone comes in liquid or powder formulations, at a concentration of 5 percent active ingredient. Rotenone should be applied at a rate of 2 to 3 ppm (2.7 pound/acre-foot of granular = 1 ppm), 5.4 to 8.1 pounds per acre-foot of actual product. The volume of water in the pond (in acre-feet), or that remaining after draw-down, must be estimated so this concentration of rotenone can be calculated. One gallon of the liquid rotenone formulation (5 percent) is sufficient to treat approximately 3 acre-feet of water at 1 ppm or 1 acre-foot at 3 ppm. The acre-feet in a particular pond can be calculated by multiplying the surface area in acres times the average depth in feet. For example, a 2-acre pond with an average depth of 6 feet would have 12 acre-feet and would require 4 gallons of the liquid 5 percent formulation to treat at a concentration of 1 ppm; 8 gallons for 2 ppm, etc.
Powdered rotenone should be mixed into a “soupy” consistency with water (about 2 gallons per pound of powder). Liquid rotenone also should be diluted with water at a rate of about 10 gallons of water to 1 gallon of rotenone. Apply rotenone evenly over the pond using buckets, sprayers, or pumps. If the pond is greater than 4 feet deep, use a hose to pump rotenone into deep sections of the pond. Rotenone applied properly and at recommended rates will not harm most livestock, even if they drink the water. Pigs, however, might be affected by the rotenone formulation, and ducks and geese may suffer if they gorge themselves on dead or dying fish. Caution: make sure no water containing rotenone runs off your property to kill fish elsewhere!
Rotenone is usually applied in the fall when water temperature is between 65º and 75º F. If applying at other times of the year, you must take special precautions. Contact a district fisheries biologist or county Extension office for additional information on purchasing and applying rotenone.
Rotenone will dissipate within 3 to 10 days, depending on weather conditions. Generally it is safe to restock 2 to 3 weeks after applying rotenone. To check for the presence of rotenone, place a few small bream in a minnow bucket and float it in the pond.
If the fish are still alive after 24 hours it is safe to restock. In very cold weather rotenone may be toxic for as long as a month.
Management of Recreational Fish Ponds Series