Electric Knifefish, Hypopomidae, are small freshwater fish found in
still and slow moving waterways in South America. They are members of the Order
Gymnotiformes, which also includes the Electric Eel, Electrophorus electricus, and like it are capable of generating
electrical pulses within their bodies, but unlike the Eel are not capable of
producing a pulse of sufficient intensity to be used for capturing prey or
defending against predators, though they are able to use it for sening and
exploring their environment, and communicating with other members of the same
species.
In a paper published in the journal ZooKeys on 28 August 2013, John Sullivan
of the Cornell University Museum of Vertebrates, Jansen Zuanon of the InstitutoNacional de Pesquisas da Amazônia, and Cristina Cox Fernandes, also of the Instituto
Nacional de Pesquisas da Amazônia and of the Biology Department at the Universityof Massachusetts, describe two new species of Electric Knifefish from the
Amazon river system.
Both the new species are placed in the genus Brachyhypopomus, which is distinguished by having notably shorted
snouts than other members of the Family Hypopomidae, but whereas other members
of the genus, and indeed family, are toothless, the two new species were found
to have small, needle-like teeth on their premaxillae (the bone that forms the
front part of the upper jaw). For this reason Sulivan et al. erect a new subgenus, Odontohypopomus
(‘Tootherd Knifefish’), in which both the new species are placed.
The first new species is named Brachyhypopomus
(Odontohypopomus) walteri, in honour of Walter
Heiligenberg (1938–1994) of the Scripps Institute of Oceanography, for his work
on the neurophysiology and behaviour of electric Fish. The species was found in
‘floating meadow’ ecosystems along the Amazon and Solimões River systems, from
the Río Napo drainagealong edge of Lago Anangucocha in Ecuador to the mouth of
the Amazon River.
Specimen of Brachyhypopomus
walteri, (total length 163 mm, length to end of anal fin 126 mm), sex
undetermined,Paraná do Paracuúba, Amazonas, Brazil. Preserved whole specimen
shown above close-up view of specimen immediately post-mortem. Scale bars equal
1 cm. Sullivan et al. (2013).
Adult specimens of Brachyhypopomus
(Odontohypopomus) walteri examined range from 116 mm to 175
mm in length. They are yellow in colour and semi-transparent, with their gills
appearing cherry red through the body wall, while the gut is dark and the swim
bladder light. Many specimens had banding on their sides, which varied in both
darkness and extent; in some specimens this was restricted to the dorsal side,
in others the banding was also present on the underside, although narrower.
The second new species is named Brachyhypopomus
(Odontohypopomus) bennetti, in honour of Michael Bennett
of the Albert Einstein College of Medicine at Yeshiva University, for his work
on electric fish neurophysiology. This species was also found in ‘floating
meadow’ ecosystems, from Colombia, Ecuador and Peru in the west to the mouth of
the Amazon in the east.
Specimen of Brachyhypopomus
bennetti, (total length 215 mm, length to end of anal fin 171 mm),
female,Paraná do Paracuúba, Amazonas, Brazil. Preserved whole specimen shown
above close-up view of specimenimmediately post-mortem. Scale bars equals 1 cm.
Sullivan et al. (2013).
Adult specimens of this species examined ranged from 98 mm to 215 mm
in length. They were yellowish tan in colour, but not transparent, with similar
banding to Brachyhypopomus (Odontohypopomus) walteri.
The two new species are very similar, and inhabit essentially the
same environment. However one important way in which they do differ is in the
electrical organ of Brachyhypopomus (Odontohypopomus) bennetti, which is considerably larger than that of Brachyhypopomus (Odontohypopomus) walteri,
or indeed most Knifefish, and produces a monophasic electrical pulse (a short
burst of positive charge) rather than a diphasic electrical pulse (a short
burst of positive charge followed by a short phase of negative charge) as seen
in most Gymnotiforme Fish.
Effect of loss of caudal portion of body by predation
on electric organ discharge (EOD)waveform in three species of Brachyhypopomus. Undamaged individuals
indicated by black dots and blackEOD trace, those with regenerating caudal body
following substantial injury with red (A) Brachyhypopomus pinnicaudatus specimens
93-20 (above) and 93-25 (below) (B) Brachyhypopomus walterispecimens
93-188/2 (above) and 93-187-1(below). Damaged specimen 93-140 (blue trace) not
shown (C) Brachyhypopomus bennetti
specimens 93-37/1 (above) and 93-37/3 (below). EODs shown with head positivity
upwards and amplitude-normalized. Sullivan et
al. (2013).
It has previously been speculated that variations in the electrical
emissions of Gymnotiforme Fish may reflect variations in water conductivity,
but the two species of Odontohypopomus
live alongside one-another, so this seems unlikely to be the case in this instance.
A monophasic pulse has only been recorded in two other species of Gymnotiformes,
one of which is the Electric Eel, Electrophorus
electricus, which occurs in the same floating meadows as the two Odontohypopomus species, and which is
predatory in nature. Sullivan et al.
suggest that Brachyhypopomus (Odontohypopomus) bennetti may be able to use its monophasic pulse to fool Electric
Eels, or other predators which avoid dangerous Electric Eels but consume
Knifefish.
The habitat of Brachyhypopomus
(Odontohypopomus) walteri and Brachyhypopomus (Odontohypopomus)
bennetti. Paraná do Paracuúba, south
of Manaus, Brazil, approximately 03°12.6'S, 59°59.4'W. Sullivan et al. (2013).
However Sullivan et al. also
note that Knifefish frequently lose their tails due to predation and that this
causes their electrical pulses, in particular the second, negative, phase of
their pulses, to become much weaker. They also not that the electrical pulses
of Brachyhypopomus
(Odontohypopomus) bennettiis not affected by the lose of
its tail, and suggest that the monophasic pulse might be an adaptation that
lets the Knifefish endure such attacks with less loss of electrical pulse
function.
See also…
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known species, of which 18 are found in the Peruvian Amazon Basin. They are
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females and typically being more brightly coloured.
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freshwater Fish from a location in the Río Chubut area of Argentine
Patagonia, which he believed to have originated in the Cretaceous in a
paper in the journal Physis. Since this time the date estimates of this
locality has altered somewhat, and they are now believed to be...
Armoured Catfish (Loricariidae) are distinctive Catfish (Siluriformes) with bodies covered in bony armoured plates found only in South America. They are a diverse group, with a high number of species, many of which have very limited distributions, and several new...
A freshwater Coccolepidid Fish from the Late Jurassic of Patagonia. In 1943 palaeontologist Alejandro Bordas described a number of fossil
freshwater Fish from a location in the Río Chubut area of Argentine
Patagonia, which he believed to have originated in the Cretaceous in a
paper in the journal Physis. Since this time the date estimates of this
locality has altered somewhat, and they are now believed to be...
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