I have a 1 acre pond in Lebanon Ohio. It is about 12' deep with tapered...

Asked October 3, 2019, 4:26 PM EDT

I have a 1 acre pond in Lebanon Ohio. It is about 12' deep with tapered sides. I run a pump most of the time. The pond is always clear maybe a few weeks of algae a year. Never any smell. A few years ago I bought 40 12" paddlefish. Put them in and never saw them again. I often would look and wonder if my $400 investment was still in there. Three years went by and the pond got filled with green algae. I put in some copper crystals. Three days later 17 large Pfish floated up dead. They were 3 and 4 feet long. One was so big it was longer than the tailgate of my truck. It was a very confusing day. I was happy the fish will thrive in my pond but very mad at myself for needlessly killing such a beautiful peaceful creature. I want to try it again but i'm afraid of the algae. It has been several years and every year I long for the fish. What can I put in to kill the algae with out killing those wonderful fish. I do have cats, bass and grass carp all live together fine. All i care about is the Paddle fish. So what will kill the algae with out killing the paddle fish. Any help your can tell me would be greatly appreciated. Thanks


2 Responses

1) Paddlefish aren't a recommended species of fish for ponds in Ohio. I'm a little surprised they lived that long. I wouldn't add more back into the pond.

2) When you kill large quantities of vegetation in a pond, the dying vegetation can consume large quantities of oxygen. So, if you killed too much at one time, then problems for fish could occur, particularly large fish because they need more oxygen.

3) During hot weather, oxygen levels are low. Killing weeds when temperatures are high can make the problem worse.

4) When pond temperatures are high and we get cold summer rains, then a pond can "turn over", which means that the oxygenated areas in the pond flip. The bottom of the pond (where the paddlefish live) might have lost all of it's oxygen and thus the big fish suffocated.

5) Copper sulfate is the best chemical alternative if used properly.

Your fish may have died because of killing the algae, but I'm more inclined to believe it was a combination of multiple factors that led to a pond turnover.

Greg Meyer

Greetings Anonymous,

Greg's answer above is good (and much more eloquently concise than I'm capable of), but I did want to add some info related to paddlefish specifically.

Paddlefish, of course, are large, open-water filter feeders. They need productive water that produces high densities of plankton to thrive. Aquaculture (farming) of paddlefish is actually relatively common in reservoirs and larger ponds. However, paddlefish aren't often stocked to smaller recreational ponds and are rarely stocked for aquaculture purposes to ponds of less than 5 acres or so. If curious, see Mims (2001): http://citeseerx.ist.psu.edu/viewdoc/download?doi=

Following label recommendations, copper is the most commonly applied algaecide. While some fishes are sensitive to copper (e.g., trouts, minnows like grass carp, etc.), paddlefish is not among them. In fact, copper is specifically recommended for algae treatment in paddlefish ponds by the textbook Paddlefish Aquaculture (Mims and Shelton, eds. 2015).

However, paddlefish are highly susceptible to low-oxygen conditions. As Greg alludes, the more likely scenario is that copper killed enough algae in your pond to slow oxygen production via reduced photosynthesis and the rate of oxygen consumption as the algae decomposed in warm water. Resultant low-oxygen stress manifested first as paddlefish mortality simply because they're more sensitive to low-oxygen conditions than more common pond species. The results likely would have been similar with the effective application of any algaecide/herbicide.