Receptor Organs Filter Background Noise

Biological Strategy

Elephant fishes

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Sense Electricity/Magnetism From the Environment

Some living systems use electric or magnetic signals as a way to receive information from their environment. Magnetic and electric fields can help such living systems determine direction, altitude, or location, and electric fields also help living systems find other living systems. Detecting and interpreting electrical and magnetic signals requires specialized techniques. For example, mud-dwelling bacteria use crystals composed of magnetite to sense geomagnetism, which helps orient the bacteria to burrow deeper into the mud.

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Differentiate Signal From Noise

The environment surrounding any living system is full of signals, such as smells, sounds, electricity, magnetism, and more. Too many signals at once can be overwhelming, making it difficult to locate and react to any particular signal. To address this, living systems must differentiate among all signals, or “noise,” so they can focus on those they really need. During mating season, for example, male frogs gather close together in large groups to call for females. Despite their overwhelming, collective noise, females are able to find a particular male whose call is attractive to her. This is because the males use desynchronized calling, enabling individual recognition.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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Receptor organs in the skin of weakly electric fishes filter out background noise and enable communication using cells as capacitors.

Weakly electric fishes can both generate and sense electric fields. Changes in the electric field around the fish provide information on its surroundings, including whether there are prey, predators, or potential mates nearby. Being able to perceive their surroundings with an electric sense is helpful for these fishes that are typically active at night and live in murky streams and rivers.

A weakly electric fish can sense low and high frequency signals. The Earth’s electromagnetic field and all living organisms moving in the water contribute to a constant, very low frequency electrical field. Weakly electric fishes, however, can actively generate high frequency electric signals using specialized electric organs. These high frequency signals often vary in rate and intensity, and they are used for navigation and communication.

To detect information from the high frequency signals while filtering out the low frequency background signals, weakly electric fish use special electro-sensitive organs called tuberous receptor organs. The organ consists of a small chamber connected to the surface of the skin with a pore. Electro-sensitive cells sit at the base of the chamber. The tube leading from the surface pore to the receptor cells is partially blocked by skin cells, which appear to function like a capacitor: they offer a high resistance to constant low frequency electrical signals, but little resistance to varying high frequency signals. The folding pattern of the lining inside the tuberous organ further reduces resistance to high frequency signals. The result is that high frequency signals easily pass through to the receptor cells.

Tuberous receptor organs are especially sensitive or “tuned” to the peak frequency of signals coming from other weakly electric fishes. This enables weakly electric fish to focus in on detailed electrical communications from other electric fishes.

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Electric Signals Detect Prey

Elephantnose fish

The elongated chin on the elephantnose fish helps it hunt in murky water by sensing electric signals.

Last Updated March 24, 2020

References

“The [tuberous receptor] organs themselves consist of a roughly spherical chamber located in the epidermis…This chamber is connected to the external environment by a short canal that perforates the epidermis…the canals of tuberous organs are composed of a plug of loosely packed epithelial cells. This epithelial plug creates a capacitance in series with the receptor cells, which acts to filter out low stimulus frequencies (Bennett, 1965). Further, the walls of the canal and chamber consist of numerous layers of epithelial cells. These many epithelial layers cause the wall to have relatively low capacitance, so that there is reduced shunting of high frequencies (Bennett, 1971a).” (Tricas and Carlson 2012:716-717)

Book section

Electroreceptors and Magnetoreceptors

In: Sperelakis N, editor. Cell Physiology Source Book. 4th Edition. Waltham (MA): Academic Press. P. 705-725. | 01/01/2012 | Tricas TC, Carlson BA

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