Электрические рыбы Южной Америки: новые виды и особенности

South American electric fish

Electrophorus electricus is the best known species of electric eel. It is a South American electric fish. Until the discovery of two additional species in 2019, the genus was classified as the monotypic, with this species the only one in the genus. Despite the name, it is not an eel, but rather a knifefish. It is considered as a freshwater teleost which contains an electrogenic tissue that produces electric discharges.

The species has been reclassified several times. When originally described by Carl Linnaeus in 1766, he used the name Gymnotus electricus, placing it in the same genus as Gymnotus carapo (banded knifefish) which he had described several years earlier. It was only about a century later, in 1864, that the electric eel was moved to its own genus Electrophorus by Theodore Gill. In September 2019, David de Santana et al. suggested the division of the genus into three species based on DNA divergence, ecology and habitat, anatomy and physiology, and electrical ability: E. electricus, E. voltai sp. nov., and E. varii sp. nov. The study found E. electricus to be the sister species to E. voltai, with both species diverging during the Pliocene. Their coloration is dark gray brown on the back and yellow or orange on the belly. Mature females have a darker abdomen. They have no scales. The mouth is square and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and maintains the fish's buoyancy. E. electricus has a vascularized respiratory system with gas exchange occurring through epithelial tissue in its buccal cavity. As obligate air breathers, E. electricus must rise to the surface every ten minutes or so to inhale before returning to the bottom. Nearly eighty percent of the oxygen used by the fish is obtained in this way.

E. electricus has three pairs of abdominal organs that produce electricity: the main organ, Hunter's organ, and Sachs' organ. These organs occupy a large part of its body, and give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up so a current of ions can flow through them and stacked so each one adds to a potential difference. The three electrical organs are developed from muscle and exhibit several biochemical properties and morphological features of the muscle sarcolemma; they are found symmetrically along both sides of the eel. Electric eels use electricity in multiple ways. Low voltages are used to sense the surrounding environment. High voltages are used to detect prey and, separately, stun them, at which point the electric eel applies a suction feeding bite. Sachs' organ is associated with electrolocation. Inside the organ are many muscle like cells, called electrocytes. Each cell produces 0.15 V, the cells being stacked in series to enable the organ to generate nearly 10 V at around 25 Hz in frequency. These signals are emitted by the main organ; Hunter's organ can emit signals at rates of several hundred hertz. There are several physiological differences among the three electric organs, which allow them to have very different functions. The main electrical organ and the strong voltage section of Hunter's organ are rich in calmodulin, a protein that is involved in high voltage production. Additionally, the three organs have varying amounts of Na+/K+ ATPase, which is a Na+/K+ ion pump that is crucial in the formation of voltage. The main and Hunter’s organs have a high expression of this protein, giving it a high sensitivity to changes in ion concentration, whereas Sachs' organ has a low expression of this protein. The typical output is sufficient to stun or deter virtually any animal. The eels can vary the intensity of the electric discharge, using lower discharges for hunting and higher intensities for stunning prey or defending themselves. They can also concentrate the discharge by curling up and making contact at two points along its body. When agitated, they can produce these intermittent electric shocks over at least an hour without tiring. E. electricus also possesses high frequency–sensitive tuberous receptors, which are distributed in patches over its body. This feature is apparently useful for hunting other Gymnotiformes. The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate. Despite being the first described species in the genus and thus the most famous example, E. electricus actually has the weakest maximum voltage of the three species in the genus, at only 480 volts (as opposed to 572 volts in E. varii and 860 volts in E. voltai).

E. electricus feeds on invertebrates, although adult eels may also consume fish and small mammals, such as rats. First born hatchlings eat other eggs and embryos from later clutches. by about .