Wiktor Wise
Sharks are cartilaginous fish that possess electroreceptive ampullae of Lorenzini, which are organs that allow them to detect electric fields. This ability is known as electroreception, and it is used by sharks in the final stages of their attacks to locate their prey. Electric fish, on the other hand, are a diverse group of aquatic or amphibious animals that can generate electric fields, which they use for sensing their surroundings, communicating, and sometimes for stunning prey. Electric fish include both oceanic and freshwater species, and among them are the neotropical knifefishes, also known as South American knifefishes, which are capable of electrolocation. So, while sharks possess electroreceptive abilities, they are not neotropical electric fish.
| Characteristics | Values |
|---|---|
| Sharks | Cartilaginous fishes |
| Neotropical electric fish | Electric eel, South American knifefishes, Gymnotiformes |
| Sharks' electrolocation ability | Most electrically sensitive animals, responding to direct current fields as low as 5 nV/cm |
| Electric fish electrolocation ability | Produce weak electric fields to locate prey, for defence, or to stun prey |
| Electric eel | Nocturnal, air-breathing, poor vision, hearing |
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What You'll Learn
Sharks are not electric fish
Sharks are cartilaginous fishes, and while they possess electroreceptive capabilities, they do not generate electric fields. Instead, sharks rely on electrolocation using their ampullae of Lorenzini, which are electroreceptive organs that evolved early in the history of vertebrates and are found in both cartilaginous and bony fishes. Sharks are the most electrically sensitive animals known, responding to direct current fields as low as 5 nV/cm. This allows them to detect the electric fields generated by the muscle movements of their prey.
Electric fish, on the other hand, are capable of generating electric fields for electrolocation, communication, and sometimes for predation and defence. The electric organ in electric fish can be derived from muscle tissue or nerve tissue. In marine fish, the electric organ consists of many electrocytes in parallel, resulting in low voltage, high current electric discharges. In freshwater fish, the electric organ has numerous cells in series, leading to high voltage, low current discharges.
The Gymnotiformes, also known as the South American or Neotropical knifefishes, are an example of electric fish. They include strongly electric species like the Electrophorus electricus (electric eel) and many other weakly electric species. These fish possess specialised electric organs that release electric discharges for electrolocation, communication, and sometimes for predation and defence.
While sharks are not electric fish, they have remarkable electroreceptive abilities that allow them to sense and respond to extremely low electric fields, showcasing their unique adaptation to the aquatic environment.
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Sharks have electroreceptive ampullae of Lorenzini
Ampullae of Lorenzini are present in both cartilaginous fishes (sharks, rays, and chimaeras) and bony fishes (coelacanths and sturgeons). They are modified parts of the lateral line system and are primarily sensitive to electrical fields. They form a series of tube-like structures beneath the skin, with the tubes radiating out in many directions. These tubes are filled with a collagen jelly, a hydrogel that has one of the highest proton conductivity capabilities of any biological material. The ampullae of Lorenzini detect electric fields in the water by measuring the potential difference between the voltage at the skin pore and the voltage at the base of the electroreceptor cells.
The function of the ampullae of Lorenzini was discovered in 1678 by the Italian physician Stefano Lorenzini, who found them while dissecting sharks. However, their electroreceptive capabilities were not established until 1960, when R.W. Murray conducted behavioural and physiological studies. These studies showed that the receptor cells at the base of the ampullae respond to mechanical stimulation, temperature changes, salinity changes, and electric fields.
The electroreceptive capabilities of sharks are extremely sensitive, with a threshold of sensitivity as low as 5 nV/cm. This allows them to detect the weak electric fields produced by the muscle contractions of their prey. Sharks rely on electrolocation using their ampullae of Lorenzini in the final stages of their attacks, as demonstrated by the robust feeding response elicited by electric fields similar to those of their prey.
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Electric fish produce weak electric fields
Electric fish can also use these weak electric fields for communication. They can modulate the electrical waveform they generate to attract mates and engage in territorial displays. For example, male electric fish can sing electric courtship songs to females, and males of certain species may produce a continuous electric "hum" to attract females.
In addition, electric fish can use weak electric fields for defence against predators. This is known as signal cloaking, where the fish produces broad-frequency electric fields close to its body that merge over space to cancel out the low-frequency spectrum at a distance, making it harder for predators to detect.
Two groups of weakly electric fish that use active electrolocation are the order Gymnotiformes (neotropical knifefishes) and the family Mormyridae (African elephantfishes). These fish are capable of generating small electrical pulses or producing a quasi-sinusoidal discharge from their electric organs.
Sharks are not considered neotropical electric fish, but they do possess electroreceptive ampullae of Lorenzini, which are ancient electroreceptors found in cartilaginous fishes. These organs allow sharks to detect electric fields, particularly in the final stages of their attacks on prey. While sharks themselves do not produce weak electric fields, they are capable of detecting the weak electric fields produced by other electric fish.
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Electric eels are not true eels
Electric eels were first described by Carl Linnaeus in 1766, based on early field research conducted in South America. In 1864, Theodore Gill moved the electric eel to its own genus, Electrophorus, derived from the Greek words "ḗlektron" and "phérō", meaning "electricity bearer". Electric eels have poor vision and are mostly nocturnal, hunting and navigating primarily using electrolocation. They are also air-breathing, needing to surface every ten minutes to breathe, unlike true eels which can breathe underwater using gills.
Electric eels have three electric organs that contain cells called electrocytes, which create an electrical current of up to 600-860 volts when the eel senses prey or feels threatened. This ability to generate electricity is what gives electric eels their name, as they can stun their prey with powerful electric shocks. The electric eel's ability to produce electricity was first studied in 1775, and this research contributed to the invention of the electric battery in 1800.
The electric eel is a unique and fascinating creature, wrongly named due to its eel-shaped body. However, it is not a true eel but rather a member of the knifefish family, with its own distinct characteristics and abilities. Electric eels showcase the incredible adaptations that certain fish have evolved to navigate and hunt in their specific environments, highlighting the diversity and complexity of the natural world.
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Electric fish are found in both oceanic and freshwater habitats
Electric fish species that live in habitats with few obstructions, such as some bottom-living fish, display electric features less prominently. Electric fish that inhabit environments with many obstacles, such as caves, murky water, or night-time conditions, rely more on electrolocation.
In passive electrolocation, electric fish detect the electric fields created by the muscle movements of their prey. In active electrolocation, electric fish generate a weak electric field to distinguish between conducting and non-conducting objects in their surroundings. Active electrolocation is practised by two groups of weakly electric fish: the order Gymnotiformes (neotropical knifefishes) and the family Mormyridae (elephantfishes), and by the monotypic genus Gymnarchus (African knifefish).
The amplitude of the electrical output from electric fish can range from 10 to 860 volts with a current of up to 1 ampere, depending on the surroundings, such as the varying conductances of salt and freshwater. Strongly electric marine fish give low-voltage, high-current electric discharges. In saltwater, a small voltage can drive a large current due to the low internal resistance of the electric organ. In contrast, freshwater fish have high-voltage, low-current discharges because the power is limited by the voltage needed to drive the current through the high resistance of the medium.
While sharks are not considered electric fish, they are highly electrically sensitive and rely on electroreception using their ampullae of Lorenzini to locate prey. Sharks are euryhaline, meaning they can regulate their bodies to adapt to a wide range of salinities and are found in both oceanic and freshwater habitats.
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Frequently asked questions
A neotropical electric fish is any fish that can generate electric fields, whether to sense things around them, for defence, or to stun prey. They are known for their ability to produce electricity within their bodies.
No, a shark is not a neotropical electric fish. Sharks are cartilaginous fishes that rely on electroreception using their ampullae of Lorenzini to locate prey. They are, however, the most electrically sensitive animals known.
Some examples of neotropical electric fish include the electric eel, bluntnose knifefish, and the African elephantfish.
They use electricity to navigate, find food, and defend themselves. They produce weak electric fields to image their surroundings, especially in dark or murky waters. They can also use electricity to stun their prey.
