''Sternarchogiton labiatus'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of weakly electric knifefish in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Apteronotidae The ghost knifefishes are a family, Apteronotidae, of ray-finned fishes in the order Gymnotiformes. These fish are native to Panama and South America. They inhabit a wide range of freshwater habitats, but more than half the species in the family ...

. Its species name ''labiatus'' comes from the Latin ''labium'', meaning "lip", referring to a distinctive three-lobed structure on its lower lips. ''S. labiatus'' is only known from the Tefé River, at a depth of , and from the lower Rio Negro, in the Amazon River basin. They have been captured from both

whitewater Whitewater forms in a rapid context, in particular, when a river's gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that froths, making the water appear opaque and ...

and blackwater habitats. ''S. labiatus'' has a laterally compressed, knife-shaped body with a nearly straight dorsal profile and a long

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

. The head is laterally compressed, with a curved dorsal profile and small eyes that are covered by a thin membrane. The mouth is terminal, with a three-lobed rigid structure consisting of a pair of smooth, hard, bulbous swellings along the lower lip and a medial spur that projects down and forward. The lower jaw is longer than deep, bearing two rows of conical teeth numbering 17 plus 4 replacements each. There are upper and lower pharyngeal tooth plates with 5-6 and 8-9 teeth respectively. There is no

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

in the

cranium The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

or the three-lobed structure. The

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

s are broad and pointed, with 12-14

ray Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (g ...

s. The anal fin rays number 156-168. The

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, r ...

is compressed and moderately long, with a small lanceolate

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

containing 15-16 rays. The coloration is dark brown, becoming darker on the back and head. Brown chromatophores are lightly speckled on the

pterygiophore A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

s (supporting bones) of the anal fin. The pectoral fins are

hyaline A hyaline substance is one with a glassy appearance. The word is derived from el, ὑάλινος, translit=hyálinos, lit=transparent, and el, ὕαλος, translit=hýalos, lit=crystal, glass, label=none. Histopathology Hyaline cartilage is ...

with dark tips, the anal fin is

with a scattering of light brown chromatophores and a slightly darkened margin, and the caudal fin is very dark brown to black. ''S. labiatus'' grows to about . The structure on the lower lip of ''S. labiatus'' has been speculated to function in electroreception for locating

prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

. Like other apteronotids, these fish generate a continuous weak

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

for the purposes of electrolocation and

communication Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...

. The

electric organ discharge An electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it">Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired ...

(EOD) of ''S. labiatus'' has a

fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'', is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. In ...

of 1160-1587 Hz and two phases; there is no known sexual dimorphism in

waveform In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electronic ...

or frequency.

Reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...

is believed to occur after the onset of the rising water period in October.

References

Apteronotidae Weakly electric fish Fish of the Amazon basin Knifefish of Brazil Endemic fish of Brazil Fish described in 2007 {{Gymnotiformes-stub