By Steven Bardin M.S.
Imagine you purchased the perfect largemouth bass lake. Its 20 acres has standing timber along one bank, a rock ledge on the opposite bank, just the right amount of lily pads growing next to the boat ramp, and a large floating dock. It looks pristine and and you are ready to fish. Your first cast gets hit immediately as the lure splashes into the water. You retrieve a 7 inch green sunfish. The next cast same thing but this time its an 8 inch crappie on the end of the line. You fish all day and catch small bass, crappie, and green sunfish. As you load the boat and head to the house you think what in the world is going on in this lake, where are all the big fish, and most importantly what do I do next?
Most likely your next step would be to call your favorite fisheries professional, discuss your day, and schedule an electrofishing survey. Weeks later during the survey your fears are confirmed and there are way to many crappie, green sunfish, and largemouth bass in the lake. Also, you find that your entire forage fish population is based on larger gizzard shad. Just when you think it could not get any worse you notice a few small black catfish that turn out to be mudcat. At this point you know and the fisheries biologist knows this is bad. After the survey the biologist tells you about the different fish species and what they all mean to the fishery. He then says the words you fear most ” You should start over”. Basically the biologist is telling you that the lake has many fish species which make achieving your goal difficult. Combined they make it nearly impossible. You may with time, tons of effort, and a large budget make small improvements but the only way to reach your goal is to start over.
This is where rotenone enters the story. Rotenone is a piscicide and a naturally occurring compound that can be found in several plants stems, seeds, and roots. This chemical has been used for centuries to poison fish. It effects cellular respiration and quickly causes fish to loose the ability to absorb oxygen into their cells. Rotenone is not species specific and will effect all fish present in the lake.
Considering the facts that rotenone restricts cellular ability to absorb oxygen and dissolved oxygen is lowest in warm water it is most often recommended to apply the chemical during hot summer days. Many fish species will have lower oxygen tolerances and therefore a slightly higher tolerance to rotenone concentrations. Rotenone is applied by mixing the chemical with water and distributing it at multiple depths to cover the entire water body evenly. The amount of rotenone to be used is based on the acre-ft of water currently in the lake. Many times lake owners will pump water levels down to save on time to apply and chemical needed. Depending on the concentration of rotenone used fish can be restocked into the water body within 4-6 weeks and you can get back to achieving your goals with a fresh start.