Evolution and Phylogeny
– All fish and vertebrates use electrical signals in their nerves and muscles.
– Cartilaginous fishes and some basal groups use passive electrolocation.
– Knifefishes and elephantfishes actively electrolocate using weak electric fields.
– Electroreception is an ancestral trait in vertebrates.
– Ampullary electroreception evolved from mechanical sensors in lateral line organs.
Weakly Electric Fish
– Weakly electric fish generate a discharge of less than one volt.
– They use electric fields for navigation, electrolocation, and communication.
– Major groups of weakly electric fish include Osteoglossiformes and Gymnotiformes.
– Mormyridae and African knifefish are examples of weakly electric fish.
– These groups have convergently evolved similar behavior and abilities.
Strongly Electric Fish
– Strongly electric fish have an electric organ discharge powerful enough to stun prey.
– Examples include electric eels, electric catfishes, electric rays, and stargazers.
– Electric eels can deliver substantial electric power and exceed pain thresholds.
– Strongly electric fish can leap out of the water to electrify predators directly.
– Amplitude of electrical output can range from 10 to 860 volts with a current of up to 1 ampere.
Electric Organ Anatomy
– Electric organs vary widely among electric fish groups.
– They evolved from excitable, electrically active tissues.
– Electric eels have three electric organs, with the main organ providing high voltage.
– Anatomy of electric organs is adapted to match the impedance of the environment.
– Electric organs are specialized for producing strong electric fields for various functions.
Physiology and Behavior
– Electric organs are made up of electrocytes.
– Electrocytes create and store electrical energy.
– Sodium channels in the anterior ends of electrocytes react to stimuli from the nervous system.
– Sodium-potassium pumps are present in the posterior ends of electrocytes.
– Neurons release acetylcholine, triggering sodium ions to flow into the electrocytes.
– Electric organ discharges (EODs) vary with time for electrolocation.
– EODs can be in the form of pulses or waves.
– Electric fishes use EODs for communication, hunting, or defense.
– The electric signals are often simple and stereotyped.
– Weakly electric fish can communicate by modulating their electrical waveform.
– Modulating the waveform can be used to attract mates or in territorial displays.
– Electrical waveforms may differ between males and females.
– Electric catfish use electric discharges to ward off other species.
– Ritualized fights with open-mouth displays and bites are used against their own species.
– Electric fish experience interference when their electric fields overlap.
– Jamming avoidance response occurs when fish are exposed to a slow beat.
– Fish adjust their frequency to avoid interference with neighboring fish.
– Electric fish have evolved jamming avoidance responses to overcome interference from conspecifics.
– High-frequency electric fields can degrade electrosensory inputs, affecting the jamming avoidance response.
– Electric fish use electric signals for communication and social interactions.
– Waveform discrimination and phase sensitivity play a role in electric communication.
– Predation enhances complexity in the evolution of electric fish signals. Source: https://en.wikipedia.org/wiki/Electric_fish
An electric fish is any fish that can generate electric fields. Most electric fish are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family (Uranoscopidae). Electric fish, although a small minority of all fishes, include both oceanic and freshwater species, and both cartilaginous and bony fishes.
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Electric fish produce their electrical fields from an electric organ. This is made up of electrocytes, modified muscle or nerve cells, specialized for producing strong electric fields, used to locate prey, for defence against predators, and for signalling, such as in courtship. Electric organ discharges are two types, pulse and wave, and vary both by species and by function.
Electric fish have evolved many specialised behaviours. The predatory African sharptooth catfish eavesdrops on its weakly electric mormyrid prey to locate it when hunting, driving the prey fish to develop electric signals that are harder to detect. Bluntnose knifefishes produce an electric discharge pattern similar to the electrolocation pattern of the dangerous electric eel, probably a form of Batesian mimicry to dissuade predators. Glass knifefish that are using similar frequencies move their frequencies up or down in a jamming avoidance response; African knifefish have convergently evolved a nearly identical mechanism.
