I recently worked with a company who performs ecology experiments in streams and lakes. They came to me needing an underwater electrical fence to keep fish, crawdads, etc out of certain areas of the stream to see what the impact would be if said critters didnt exist. Thus, the Fish Zapper was born!
The fish zapper, more boringly referred to as the under water ex-closure, delivers a 20 – 100uS wide 500 volt pulse to two concentric rings that form the electrodes at a rate of 1 – 20 Hz. We found out rather quickly that running an electric current through underwater electrodes will corrode and destroy them due to the electrolysis of water. A DC current of a few hundred mA will completely dissolve a 12 gauge aluminum or copper electrode in about a day. To combat this problem, we used a low duty cycle pulsed system and stainless steel rings. We had a Mechanical Engineering intern who designed the ring system, and more info can be found about it
The zapper circuit was comprised of a fly back voltage regulator to generate 500 VDC from a 12 volt input, and store it on the big blue capacitor in the photo below. A 555 timer circuit was used to generate the 100uS wide, 20Hz pulses that was used to trigger a Mosfet which would dump the 500V into the electrodes of the fish zapper.
So far the zapper has been tested on crawdads, and it definitely repels them. Sticking ones hand in the water will give a tingle, with pain increasing as you get closer to the electrodes.
Test subject A 3 Zero (pictured below) was the original and most beloved test subject in all of the lab. He dedicated his life to this project, endured starvation, electroshock, and had to constantly battle with the larger, nastier species of crawdad that we obtained from a Cajun restaurant. He died alone in his tank from unknown causes on July 23, 2013. Memorial services were held at the garbage can out back, and a permanent memorial was erected under the pine tree in the west parking lot.
R.I.P Test Subject A 3 Zero.