Electroreception is the biological ability to sense electrical fields and impulses. Although very uncommon in mammals, electroreception is a common ability in many fish species. Since air is a very poor medium for electricity, electroreception is a trait found primarily in water; both freshwater and saltwater.

Since electrical impulses cause muscle contraction, every muscle movement produces an electrical discharge. This is particularly useful for predators, such as sharks, who are seeking prey. Normal movement causes low levels of impulses, while a wounded fish would cause large levels of impulses. Because sharks are among the most sensitive to electrical impulses, they are also among the greatest predators of the ocean. Through the darkness of the depths of the ocean or the cover of murky water, sharks can easily find their prey. Aside from enabling a fish to find its prey, electroreception is beneficial in a variety of other ways. It allows fish to evade predators, communicate with other fish, navigate at night or during other moments of low visibility, find objects in the water, and it aids in reproduction. Electrical currents caused by the earth’s magnetic fields can also act as a biological compass for animals that possess this incredible ability.

Some downriggers offer the ability to use positive ions to create electrical fields in the water. This is referred to by the Cannon line as “positive ion control”. This process involves a voltage difference between the downrigger wire and the boat that causes an electric field. The size of this field is somewhat dependent on the size of the boat and the materials of which it is made. Some fish are attracted to a small positive charge, while a strong positive or negative charge will repel them. Positive ion control can be extremely useful when targeting these types of fish. Catfish, trout, salmon, and bass are among the species of game fish attracted by positive ion control. Since different voltage levels tend to attract different types of fish, it is important to know what species is being targeted. When used correctly, positive ion control offers a competitive edge to both the serious and the occasional fisherman.