Electronarcosis... not as shocking as you may think

When people think of using electricity on fish, the usual first reaction is that it can’t be a good thing. There are volumes of scientific literature investigating the effects of electricity on fish behavior, physiology, reproduction, survival, etc. Most of them discuss the pros and cons of using electricity to capture fish – electrofishing. You may have heard of it… people have been using electrofishing since the early part of the 20th century. It has merit, if done correctly. But, that is a discussion for another day.

Did you know that you can also use electricity to put fish to sleep? It is an extremely effective method of putting a fish into a state of narcosis – electronarcosis. You use constant DC voltage… the same type of power found in your car battery. In fact, we hook up a power supply to a car battery! We just put the fish in a cooler full of water with aluminum electrodes on each end that are hooked up to the power supply, turn up the power to around 40 volts, but only about 0.1 amp, and the fish “falls asleep”. What is really happening is that the electrical field is inhibiting any communication between the brain and the rest of the fish’s body, resulting in a completely relaxed fish presumably feeling no pain.

Why would you want to do this? As fish biologists, we handle fish all the time to identify them, measure them, tag them, collect tissue samples from them, or for any number of other reasons. Some of the activities can result in elevated stress levels from all of the handling. So, we use anesthetics to relax the fish, reducing stress and decreasing related impacts such as changes in behavior, growth, or reproductive potential. Historically, one of the most common anesthetics has been a chemical called MS-222. It has a really long name and all kinds of research associated with it… Google it! Most notably, it is one of the few chemical anesthetics approved by the Food and Drug Administration for use on fish that could potentially be harvested for consumption. But, since it has some nasty side effects (such as being a possible carcinogen), if it is used on fish that could potentially be harvested for consumption, those fish must be held for 21 days prior to release to ensure the chemical is out of the fish’s system. This requirement presents problems with adult salmon and steelhead in the Pacific Northwest. Because these fish could potentially be harvested, biologists can’t use MS-222 on them. The alternative has been using no anesthetic on them, probably increasing handling stress in the fish, with unknown consequences.

We finally have a solution to this problem… ELECTRONARCOSIS!

Using this approach, biologists can now release the fish immediately after being anesthetized… literally. With MS-222 or other chemical anesthetics, it takes a while (sometimes 15-30 minutes) for a fish to recover from the anesthetic. With electronarcosis, as soon as you turn the power off, the fish is upright, swimming and ready for release within 10 seconds.

We have been using this on bull trout to surgically implant radio tags (again… a story for another day). Check out the video. When you see my hands go across the screen at the beginning and end, I am turning the power on (beginning) and off (end). There is enough of an electric field to put the fish to sleep, but not bother me the entire time my hands are in the water. These fish go under immediately, are relaxed throughout, are gilling (breathing) regularly, show no signs of pain at any time, and recover from the anesthetic immediately. They would be ready for release if we hadn’t just conducted major surgery on them! So, we hold them for a couple of minutes, and since we have been able to track them subsequent to tagging, we can confirm no delayed mortality.

It is pretty amazing what you can do with technology these days!