Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Rotenone

Will Rotenone also kill fry? What if it is applied a day or so before eggs hatch? Is there a chance that they could survive? Assuming it is applied correctly what percentage of the fish will die? Just curious.

Mike

There is a very good article all about rotenone in the current isssue of Pond Boss magazine. Try to read it.
Rotenone will last several days to weeks depending on several variables such as water temp, suspended solids, water chemistry, and amount of plankton in the water. It will definately kill fish fry and at lower concentrations than it would have killed larger fish of the same species. I would also bet that rotenone will kill or stop development of fish eggs due to its affects on the oxygen carrying / diffusion capacity or transfer of oxygen to the blood. Developing fish fry have circulating blood; they just don't get the oxygen from gills at this stage.

Used PROPERLY and at the correct concentration it will kill all fish present.

Green head: I agree with Bill. That rotenone article in the last issue of Pond Boss is very well done. After reading that, you should easily be able to renovate a pond fish community. I especially liked the fact that Mr. Latona talked about a 3 ppm concentration for many fishes, rather than using 1 or 2 ppm. Nothing is worse than going to all the time and trouble to renovate a pond, and then having some fish survive. Plus, it's usually the undesirable fish, such as bullheads or carp, that survive the partial kill. The same thing is true for muddy water and water with a lot of decomposing organic material (such as plants); these situations require more rotenone (as Mr. Latona indicated).

Bill: I have always been taught, and now tell my students, that rotenone will not kill fish eggs. The most common example I have heard is common carp -- if you have a early summer rotenone operation just after the carp have spawned, the water detoxifies in just a few days when temps get into the 70s F. So, the eggs may hatch after the toxicity is too low to kill the newly hatched carp fry.

Now, having said this, I don't actually have any personal experience where eggs actually did survive. We try to avoid rotenone operations near spawning times just for this reason. Perhaps some other contributor can chime in, if they have more information or personal experience.

The other "tidbit" that I was always taught, and continue to pass on is: don't let pigs near the water where you have applied rotenone. While most mammals are not affected by rotenone at the recommended dosages, pigs are supposedly very sensitive to it. Again, I have never let a pig into any treated water to "test" this piece of information! :-)

Dave

Well I lost that bet about rotenone killing fish eggs. It is a good thing I did not have the stakes very high. I had a 50% chance of winning. Just my luck! LOL.

Hey, Bill. I don't think you lost a bet. The truth, as usual, is likely somewhere in the middle.

After I wrote my reply yesterday, I did a quick search to see if I could find any papers on the effects of rotenone on eggs.

I didn't find much, and the only one I found was for trout and salmon.

For brook trout and chinook salmon, it took more than 3 ppm to kill 50% of the eggs after 96 hours in the treatment. However, lake trout were quite sensitive, and once rotenone got over 1 ppm, half the eggs would die in 96 hours.

The amount to kill the small fingerlings was VERY low. After 96 hours, half of the chinook salmon, brook trout, and lake trout would be dead at rotenone levels of 0.05 (salmon and brookie) and 0.03 (lake trout) ppm.

So, we can probably conclude that enough rotenone will kill at least some fish eggs, and that eggs seem to be a lot harder to kill than newly hatched fish. However, I didn't find any information on any of the warmwater fishes. Regardless, it's probably best not to count on the rotenone to kill fish eggs.

Once again, if any of the pond management experts have any furhter information, we'd sure like to hear from you.

Dave

Found a couple more references on the rotenone/fish egg topic.

On the Prentiss web site (they sell rotenone), I found the following.

http://www.prentiss.com/Products/fishman.htm

"Are fish eggs affected by Rotenone treatments?

Most fish eggs are 10-100 times more resistant the fish."

Then, I found the following on the Oregon Department of Fish and Wildlife web site.

http://www.dfw.state.or.us/ODFWhtml/InfoCntrFish/DiamondLake/Rotenone.html

Q. Are fish eggs affected by rotenone?

A. Research indicates that fish eggs are much more resistant to rotenone treatments than larval or adult stages. For example, newly fertilized rainbow trout eggs were 41 to 106 times more resistant; salmon eggs are 10 times more resistant than the fish and carp eggs are 50 times more resistant.

So, rotenone does kill fish eggs, but typically at much higher levels than we use for killing fish. At the current costs of rotenone, which are very high, I doubt that many people would want to go to sufficient treatment levels to kill fish.

Whew, Bill: once these questions start, they always get interesting, don't they??

Dave

Thanks guys. I appreciate your responses. Here's another question. When a pond experiences a kill in the summer due to lack of oxygen and virtually all the fish die why/how do the juvenile fish survive?