Gymnotiformes
South American knifefish Temporal range: [1]
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Apteronotus albifrons
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
(unranked): | Otophysi
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Order: | Gymnotiformes |
Type species | |
The Gymnotiformes
Description
Anatomy and locomotion
Aside from the electric eel (Electrophorus electricus), Gymnotiformes are slender fish with narrow bodies and tapering tails, hence the common name of "knifefishes". They have neither
The knifefish has approximately one hundred and fifty fin rays along its ribbon-fin. These individual fin rays can be curved nearly twice the maximum recorded curvature for ray-finned fish fin rays during locomotion. These fin rays are curved into the direction of motion, indicating that the knifefish has active control of the fin ray curvature, and that this curvature is not the result of passive bending due to fluid loading.[4]
Different wave patterns produced along the length of the elongated anal fin allow for various forms of thrust. The wave motion of the fin resembles traveling sinusoidal waves. A forward traveling wave can be associated with forward motion, while a wave in the reverse direction produces thrust in the opposite direction.[5] This undulating motion of the fin produced a system of linked vortex tubes that were produced along the bottom edge of the fin. A jet was produced at an angle to the fin that was directly related to the vortex tubes, and this jet provides propulsion that moves the fish forward.[6] The wave motion of the fin is similar to that of other marine creatures, such as the undulation of the body of an eel, however the wake vortex produced by the knifefish was found to be a reverse Kármán vortex. This type of vortex is also produced by some fish, such as trout, through the oscillations of their caudal fins.[7] The speed at which the fish moved through the water had no correlation to the amplitude of its undulations, however it was directly related to the frequency of the waves generated.[8]
Studies have shown that the natural angle between the body of the knifefish and its fin is essential for efficient forward motion, for if the anal fin was located directly underneath, then an upwards force would be generated with forward thrust, which would require an additional downwards force in order to maintain neutral buoyancy.[7] A combination of forward and reverse wave patterns, which meet towards the center of the anal fin, produce a heave force allowing for hovering, or upwards movement.[5]
The ghost knifefish can vary the undulation of the waves, as well as the angle of attack of the fin to achieve various directional changes. The pectoral fins of these fishes can help to control roll and pitch control.[9] By rolling they can generate a vertical thrust to quickly, and efficiently, ambush their prey.[7] The forward movement is determined exclusively by the ribbon fins and the contribution of the pectoral fins for forward movement was negligible.[10] The body is kept relatively rigid and there is very little motion of the center of mass motion during locomotion compared to the body size of the fish.[8]
The caudal fin is absent, or in the apteronotids, greatly reduced. The gill opening is restricted. The anal opening is under the head or the pectoral fins.[11]
Electroreception and electrogenesis
These fish possess
The electric organs of most Gymnotiformes produce tiny discharges of just a few
Taxonomy
There are currently about 250 valid gymnotiform species in 34 genera and five families, with many additional species
Order Gymnotiformes
- Suborder Gymnotoidei
- Family Gymnotidae(banded knifefishes and electric eels)
- Family
- Suborder Sternopygoidei
- Superfamily Rhamphichthyoidea
- Family Rhamphichthyidae (sand knifefishes)
- Family Hypopomidae (bluntnose knifefishes)
- Superfamily Apteronotoidea
- Family Sternopygidae(glass and rat-tail knifefishes)
- Family Apteronotidae(ghost knifefishes)
- Family
- Superfamily Rhamphichthyoidea
Phylogeny
Most gymnotiforms are weakly electric, capable of active
Actively electrolocating fish are marked on the phylogenetic tree with a small yellow lightning flash . Fish able to deliver electric shocks are marked with a red lightning flash . There are other electric fishes in other families (not shown).[13][24][25]
Otophysi
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Distribution and habitat
Gymnotiform fishes inhabit freshwater rivers and streams throughout the humid
Evolution
Gymnotiformes are among the more derived members of
Gymnotiformes has no extant species in
Approximately 150 Mya, the ancestor to modern-day Gymnotiformes and Siluriformes were estimated to have convergently evolved ampullary receptors, allowing for passive electroreceptive capabilities.[27] As this characteristic occurred after the prior loss of electroreception among the subclass Neopterygii[28] after having been present in the common ancestor of vertebrates, the ampullary receptors of Gymnotiformes are not homologous with those of other jawed non-teleost species, such as chondricthyans.[29]
Gymnotiformes and Mormyridae have developed their electric organs and electrosensory systems (ESSs) through convergent evolution.[30] As Arnegard et al. (2005) and Albert and Crampton (2005) show,[31][32] their last common ancestor was roughly 140 to 208 Mya, and at this time they did not possess ESSs. Each species of Mormyrus (family: Mormyridae) and Gymnotus (family: Gymnotidae) have evolved a unique waveform that allows the individual fish to identify between species, genders, individuals and even between mates with better fitness levels.[33] The differences include the direction of the initial phase of the wave (positive or negative, which correlates to the direction of the current through the electrocytes in the electric organ), the amplitude of the wave, the frequency of the wave, and the number of phases of the wave.
One significant force driving this evolution is predation.[34] The most common predators of Gymnotiformes include the closely related Siluriformes (catfish), as well as predation within families (E. electricus is one of the largest predators of Gymnotus). These predators sense electric fields, but only at low frequencies, thus certain species of Gymnotiformes, such as those in Gymnotus, have shifted the frequency of their signals so they can be effectively invisible.[34][35][36]
Sexual selection is another driving force with an unusual influence, in that females exhibit preference for males with low-frequency signals (which are more easily detected by predators),[34] but most males exhibit this frequency only intermittently. Females prefer males with low-frequency signals because they indicate a higher fitness of the male.[37] Since these low-frequency signals are more conspicuous to predators, the emitting of such signals by males shows that they are capable of evading predation.[37] Therefore, the production of low-frequency signals is under competing evolutionary forces: it is selected against due to the eavesdropping of electric predators, but is favored by sexual selection due to its attractiveness to females. Females also prefer males with longer pulses,[33] also energetically expensive, and large tail lengths. These signs indicate some ability to exploit resources,[34] thus indicating better lifetime reproductive success.
Genetic drift is also a factor contributing to the diversity of electric signals observed in Gymnotiformes.[38] Reduced gene flow due to geographical barriers has led to vast differences signal morphology in different streams and drainages.[38]
See also
- Electric fish
- Gymnarchus, the African knife-fish (Mormyroidea)
References
- ^ Froese, Rainer, and Daniel Pauly, eds. (2007). "Gymnotiformes" in FishBase. Apr 2007 version.
- ISBN 978-0691170749.
- ^ ISBN 0-12-547665-5.
- PMID 25043841.
- ^ S2CID 10911068.
- S2CID 2656865.
- ^ S2CID 14992273.
- ^ PMID 24925455.
- .
- PMID 24039242.
- OCLC 248781367.
- ^ Crampton, W.G.R. and J.S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. Pp. 641-725 in Communication in Fishes. F. Ladich, S.P. Collin, P. Moller & B.G Kapoor (eds.). Science Publishers Inc., Enfield, NH.
- ^ S2CID 15603518.
- PMID 20980295.
- ^ a b Albert, J. S., and W. G. R. Crampton. 2005. Electroreception and electrogenesis. Pp. 431-472 in The Physiology of Fishes, 3rd Edition. D. H. Evans and J. B. Claiborne (eds.). CRC Press.
- ^ Eschmeyer, W. N., & Fong, J. D. (2016). Catalog of fishes: Species by family/subfamily.[page needed]
- ^ .
- ^ Albert, J. S. and W. G. R. Crampton. 2005. Diversity and phylogeny of Neotropical electric fishes (Gymnotiformes). Pp. 360-409 in Electroreception. T. H. Bullock, C. D. Hopkins, A. N. Popper, and R. R. Fay (eds.). Springer Handbook of Auditory Research, Volume 21 (R. R. Fay and A. N. Popper, eds). Springer-Verlag, Berlin.
- .
- S2CID 16535732.
- ISBN 978-1118342336.[page needed]
- PMID 31506444.
- PMID 33473497.
- PMID 22606250.
- PMID 22606250.
- S2CID 35007130.
- S2CID 73442571.
- PMID 23761476.
- S2CID 73442571.
- S2CID 39794542.
- ^ Albert, J. S., and W. G. R. Crampton. 2006. Electroreception and electrogenesis. Pp. 429-470 in P. L. Lutz, ed. The Physiology of Fishes. CRC Press, Boca Raton, FL.
- S2CID 14178144.
- ^ S2CID 16787431.
- ^ PMID 10210663.
- S2CID 204994529.
- S2CID 6240530.
- ^ S2CID 195856052.
- ^ S2CID 1064883.