Black Box Techniques
Chapter VII. Electrical Sensitivity of Fish
Research into the behavior of fish in the presence of electricity started over one hundred years ago. Scientists and biologists have long been fascinated by the ability of some fish to use electricity and magnetism to navigate and find prey. Even though a lot has been learned, in many ways the field is still in its infancy. It is known that all fish have some reaction to electric stimulus in the water; but exactly how fishermen should take advantage of this, remains a mystery with most species. Let's start with a summary of what is known.
Fish use electricity in varying ways.
As early as 1917 scientific studies had revealed that a number of animals including fish, demonstrated responses to the presence of tiny electric fields in their environment. Some of the earliest work was done on catfish which turned out to be very electrically sensitive. Scientists, PARKER and VAN HEUSEN, tested blindfolded catfish in an aquarium. When glass or inert rods were inserted into the tank, there were no reactions. However, when metal rods were inserted, there were immediate reactions. With some metals, the catfish would swim to the rods and with other metals they would swim away. The reactions came from galvanic reactions between the metals and the water. Later the same scientists created the same reactions with induced electricity instead of the rods.
By the 1950's hundreds of fish were classified and ranked by their degree of response to an anode (electrical) reaction. It was learned that many fish have the capability to sense the electrical impulses given off by other fish and some can even sense the tiny voltage gradients created by ocean currents and river water movements in the presence of the earth's magnetic field. All fish have a reaction to an electrical field but it differs. Some fish are attracted to the field, some are frightened by it and attempt to hide and a third group appears to be immobilized by it. Interestingly, however, all of these groups react towards the positive charge and away from the negative. Even fish that are frightened and attempt to hide, will move in the direction of the positive anode.
In 1982 a study by Mr. L. A. Balayev of the Moscow All-Union Research Institute for Sea Fisheries concluded in part:
Fish are divided into three groups: those with an anode reaction, those without and those in the intermediate group.
Irrespective of the presence or absence of anode reaction, all species of fish distinguish the anode (+) from the cathode (-) and prefer the anode.
The anode reaction occurs in two stages: (1) distinction by the fish of the polarity of the current, (2) movement towards the anode or absence of movement depending on the ecological stereotype of behavior of the fish.
The presence of an anode reaction is characteristic of active and agile species. Fish that are not very active respond to the action of the (electric) current by hiding.
Some fish are unique in that they have special cells on their body surface that are electro receptors. These nerve cells have the specific capability of reading electric signals. Sharks, rays, sturgeon and catfish are some of the better known species of this type. Not only are they attracted by an anode reaction but they will use their electro receptors to find prey hidden or buried in the mud or sand. They can sense the electrical nerve discharges of their target.
Following are some of the scientific conclusions relating to game fish.
In the rankings of electro sensor capabilities of all fish, sharks and rays are at the absolute top of the list. Dr. Theodore Bullock of the Scribbs Institute of Oceanography, is one of the foremost world experts on Electro reception. His book Electroreception was published in 1986. Bullock ranks sharks as probably 1000 times more sensitive than any other fish. He indicates that sharks and rays have the documented capability to navigate solely using the earth's magnetic field as their guide. In the June 1991 issue of National Geographic, researcher Adrian Kalmijn noted that "a shark recognizes an electric field in the order of five-billionth of a volt per centimeter." Kalmijn offers this perspective. "Plant electrodes 2000 miles apart on the ocean floor and power them with a 1.5 volt flashlight battery. That is a very weak electric field. But every shark in between those electrodes will know what you are up to."
An interesting series of tests on sharks were run by a scientist named KALMIJN in 1971. He successfully demonstrated that sharks and rays use electro sensors to find prey buried in sand. He buried live flatfish. When sharks were stimulated to feed, they would go to the exact spot in the sand and dig out the flatfish. Kalmijn then substituted a charged wire electrode for the flatfish. The sharks would tenaciously dig to the electrode and return time and time again even though they found no prey.
Salmon do not have electro sensor cells but they have been found to be one of the species strongly attracted to an anode reaction. Research at the University of British Columbia demonstrated that salmon can distinguish the earth's magnetic field. When baby salmon in test tanks were subject to magnetic fields imposed outside the tanks, the majority of the fish would orient themselves to one side of the tank. It is believed salmon use this sense in their migration patterns. Many years ago the U.S. Fish and Wildlife Service learned that they have to be very careful with galvanic reactions (electrolysis) around culverts and salmon hatcheries.
In many instances salmon must swim through culverts or other metal structures in their upstream migration. If the dissimilar metals are used such that a negative galvanic reaction is present, the salmon will refuse to enter the culvert or structure. The Fish and Wildlife service carefully neutralizes these structures to ensure salmon passage.
In 1979 Daniel Kenichi Nomura completed his masters thesis at the University of B.C. by running controlled voltage tests aboard boats of commercial salmon trollers. For King salmon, Normura demonstrated that troll success "was higher for the positive 0.5 volts condition and not significantly different for the positive 1.0 volts condition, with respect to the paired control conditions of zero volts." The same tests for sockeye salmon showed the best attraction voltage for this fish was 1.0 volts. Nomura also attempted to prove or disprove the theory that optimum voltage has a bearing on the size of salmon caught but his results were inconclusive.
Catfish also possess electro receptor cells. Like sturgeon and sharks they use this capability to find prey in the muddy murky waters they habitate. Many cat fishermen know the old trick of throwing flashlight batteries into the water to catch catfish. The electrical charge attracts them.
Sturgeon are another species that possess special electro receptor cells. There is a row of these cells along the sturgeons snout. They use this capability to detect tiny electrical discharges from clams, mussels and other invertebrates buried in the mud or sand. Fishermen who can duplicate these nerve discharges in their bait using the Black Box technology have a fishing advantage.
Kokanee are one of the most sensitive salmon to electric voltage. Kokanee are the landlocked cousins of the sockeye salmon. With a voltage of usually .600 volts, kokanee will congregate around a downrigger wire and will follow along as you troll. Most kokanee experts rely on the Black Box to improve their catch.
Studies on trout have linked their response to electrical fields to metabolism. Active fish like trout have a higher rate of metabolism and demonstrate more electrical sensitivity. Research has shown that the best Black Box setting for most trout is .65 volts.
Laketrout have also demonstrated the capability of sensing weak electrical fields in the water. The Black Box has proven very effective in attracting them. A setting of .600 to .650 is recommended.
Salmon, trout and many other fish have what is called a lateral line down their sides. In this line there are hairlike nerve cells that can detect vibrations and weak electric fields. The same kind of cells appear on the head of the fish.
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