What Is Rotenone?
If a pond has been neglected for many years, or requires complete renovation, the only option may be cleaning the slate and restocking. When such projects arise, the first procedure is rotenone. Rote….what?
Such an example occurred in south Fort Worth. This property is the future home for a children’s home/academy. Previous use was a golf course. It has four, shallow ponds formerly maintained as retention ponds to irrigate the course. School officials want to develop them for educational projects. On special occasions, they will reward student’s hard work with a fun fishing tournament and fish fry. While touring each site, the property manager revealed several had been exposed to flooding from an adjacent creek. They contained numerous, stunted bullhead or mudcat. That revelation left no option. They must be rotenoned if we hoped to achieve optimum success with future goals for channel catfish, bass, and big bluegill.
Agricultural Extension Specialist Forrest Wynne and Extension Fisheries Specialist Michael Masser explain such undesirable species create complications that include:
- Preying on desired fish.
- Overpopulating the pond.
- Competing for food and spawning habitat.
- Water quality deterioration.
- Transmitting disease to other fish.
Although birds and similar sources are blamed for unwanted fish, in most cases, introduction is from above-described flood events or stocking by well-intending friends. Physical methods for removing unwanted fish include water draw-down, seining, or electrofishing. Those methods may be partially successful, but the most effective plan is completely draining or applying approved fish toxicants. Chlorine, rotenone, and antimycin A are the only toxicants currently approved by the Environmental Protection Agency. Chlorine is a non-restricted, general-use pesticide used as a toxicant and algaecide. Rotenone is derived from roots and stems of certain tropical and subtropical plants. Rotenone kills fish by inhibiting cellular respiration and the ability to use dissolved oxygen.
Rotenone will remove fish only when the correct concentration is applied. First procedure in determining proper amounts is calculating pond surface area and average depth. It is most effective when water temperature is cool, approximately 45 to 75-degreesF. The area should be free of aquatic plants and dense algae blooms. Water should have low dissolved oxygen, low turbidity, and low alkalinity. Rotenone is more toxic to fish in warm water, but it dissipates more quickly then and may not kill all fish present. When possible, reduce water levels. This lessens the amount of rotenone needed, thus reduces chemical costs. All areas holding water must be treated. Even footprints may hold fish larvae.
Rotenone will detoxify in one to four weeks depending on the amount applied, water temperature, and related environmental factors. The water column can be tested for residual levels by placing fathead minnows in a minnow bucket suspended at the surface. If minnows survive 48-hours, the pond should be ready for restocking.
Products containing rotenone are restricted-use pesticides. Restricted-use pesticides may be applied only by a certified, private applicator on his or her own property, or by a licensed commercial pesticide applicator. It must be applied only following label instructions. Rotenone should not be allowed to enter public waters. A land owner may be held liable if fish are killed in adjacent non-treated waters.
If considering rotenone use, please consult a professional applicator for best results. In large ponds, fish may survive untreated pockets if the entire water column is not thoroughly saturated.