The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water, these mostly nocturnal fish are capable of producing electric fields to detect prey, for navigation, communication, and, in the case of the electric eel, attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish, the glass knifefish, and the banded knifefish.
Fish anatomy is the study of the form or morphology of fish. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in living 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.
Electroreception and electrogenesis are the closely related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stun prey. The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. In passive electrolocation, objects such as prey are detected by sensing the electric fields they create. In active electrolocation, fish generate a weak electric field and sense the different distortions of that field created by objects that conduct or resist electricity. Active electrolocation is practised by two groups of weakly electric fish, the Gymnotiformes (knifefishes) and the Mormyridae (elephantfishes), and by Gymnarchus niloticus, the African knifefish. An electric fish generates an electric field using an electric organ, modified from muscles in its tail. The field is called weak if it is only enough to detect prey, and strong if it is powerful enough to stun or kill. The field may be in brief pulses, as in the elephantfishes, or a continuous wave, as in the knifefishes. Some strongly electric fish, such as the electric eel, locate prey by generating a weak electric field, and then discharge their electric organs strongly to stun the prey; other strongly electric fish, such as the electric ray, electrolocate passively. The stargazers are unique in being strongly electric but not using electrolocation.
Ampullae of Lorenzini are electroreceptors, sense organs able to detect electric fields. They form a network of mucus-filled pores in the skin of cartilaginous fish and of basal bony fishes such as reedfish, sturgeon, and lungfish. They are associated with and evolved from the mechanosensory lateral line organs of early vertebrates. Most bony fishes and terrestrial vertebrates have lost their ampullae of Lorenzini.
The Mormyridae, sometimes called "elephantfish", are a superfamily of weakly electric fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order, with around 200 species. Members of the family can be popular, if challenging, aquarium species. These fish have a large brain size and unusually high intelligence.
Peters's elephant-nose fish is an African freshwater elephantfish in the genus Gnathonemus. Other names in English include elephantnose fish, long-nosed elephant fish, and Ubangi mormyrid, after the Ubangi River. The Latin name petersii is probably for the German naturalist Wilhelm Peters. The fish uses electrolocation to find prey, and has the largest brain-to-body oxygen use ratio of all known vertebrates.
A fish is an aquatic, craniate, gill-bearing animal that lacks limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the class Actinopterygii, with around 99% of those being teleosts.
In biology, the electric organ is an organ that an electric fish uses to create an electric field. Electric organs are derived from modified muscle or in some cases nerve tissue, and have evolved at least six times among the elasmobranchs and teleosts. These fish use their electric discharges for navigation, communication, mating, defence, and in strongly electric fish also for the incapacitation of prey.
Gymnarchus niloticus – commonly known as the aba, aba aba, frankfish, freshwater rat-tail, poisson-cheval, or African knifefish – is an electric fish, and the only species in the genus Gymnarchus and the family Gymnarchidae within the order Osteoglossiformes. It is found in swamps, lakes and rivers in the Nile, Turkana, Chad, Niger, Volta, Senegal, and Gambia basins.
Marcusenius is a genus of the elephantfish group native to Africa. Its members are highly diverse in size, with the smallest species reaching less than 15 cm (6 in) and the largest more than 1 m (3.3 ft).
Mormyrus is a genus of ray-finned fish in the family Mormyridae. They are weakly electric, enabling them to navigate, to find their prey, and to communicate with other electric fish.
A Knollenorgan is an electroreceptor in the skin of weakly electric fish of the family Mormyridae (Elephantfish) from Africa. The structure was first described by Viktor Franz (1921), a German anatomist unaware of its function. They are named after "Knolle", German for "tuberous root" which describes their structure.
In physiology, an efference copy or efferent copy is an internal copy of an outflowing (efferent), movement-producing signal generated by an organism's motor system. It can be collated with the (reafferent) sensory input that results from the agent's movement, enabling a comparison of actual movement with desired movement, and a shielding of perception from particular self-induced effects on the sensory input to achieve perceptual stability. Together with internal models, efference copies can serve to enable the brain to predict the effects of an action.
In neuroethology and the study of learning, anti-Hebbian learning describes a particular class of learning rule by which synaptic plasticity can be controlled. These rules are based on a reversal of Hebb's postulate, and therefore can be simplistically understood as dictating reduction of the strength of synaptic connectivity between neurons following a scenario in which a neuron directly contributes to production of an action potential in another neuron.
The Cornish jack, Mormyrops anguilloides, is a species of weakly electric fish in the family Mormyridae, native to quiet waters in much of Sub-Saharan Africa. The largest species in its family, the Cornish jack is a nocturnal group hunter of smaller fishes, using electricity to locate its prey and communicate with other members of its group. It is a commercial game fish valued for its size and taste.
Paramormyrops is a genus of elephantfish in the family Mormyridae from Africa.
The following outline is provided as an overview of and topical guide to fish:
The expensive tissue hypothesis (ETH) relates brain and gut size in evolution. It suggests that in order for an organism to evolve a large brain without a significant increase in basal metabolic rate, the organism must use less energy on other expensive tissues; the paper introducing the ETH suggests that in humans, this was achieved by eating an easy-to-digest diet and evolving a smaller, less energy intensive gut. The ETH has inspired many research projects to test its validity in primates and other organisms.
The Mormyroidea are a superfamily of fresh water fishes endemic to Africa that, together with the families Hiodontidae, Osteoglossidae, Pantodontidae and Notopteridae, represents one of the main groups of living Osteoglossiformes. They stand out for their use of weak electric fields, which they use to orient themselves, reproduce, feed, and communicate.
