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Characins

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The vast number of small-sized fish species makes the group of fishes we commonly term characins one of the most popular for home aquaria. Characins - or more correctly characids - belong to the scientific order Characiformes. The name is derived from the Greek charax [a marine fish] plus the Latin forma [=shape]. This is a fairly recent taxonomic revision; previously these fish were all considered to be within a single Family, Characidae, included within the order Cypriniformes.

The oldest characid fossil record comes from the late Jurassic period, more than 145 million years ago. Several ichthyologists now view the characins as representing the oldest and most ancient of freshwater fishes, and Boulenger considered them the ancestors of the naked catfish, barbs, eels and Knifefish.

The ancestor of all modern Characiformes appeared when the two southern continents of Africa and South America were part of the supercontinent called Gondwana (Lundberg 1993; Orti­ and Meyer 1997). The breakup of the two continents allowed the characins in what became South America to take full advantage of the potential [=empty or not fully-exploited] ecological niches, and with the exception of the marsupials in Australia, the characids underwent explosive radiation unlike any other in all the vertebrates. The diversification of the cichlid fishes in the African rift lakes is a more recent though much smaller-scaled example.

The divergence in ecological specialization among the characids is truly remarkable. With respect to feeding, many are predatory, several are herbivore, some survive by eating fish fins and scales, some are mud-eaters, and some sift plankton from the water; in other respects, some "hop" on the substrate, some leap from the water and glide, some jump out of the water and spawn on terrestrial vegetation, some swim with their head vertically downward, some are capable of air-breathing, and some exhibit nesting behaviours and parental care. No other order of fish possesses such diversity.

There are currently more than 1674 described species in approximately 270 genera within 19 Families (Nelson, 2006). Roughly 20% of the characin families with approximately 200 species occur in Africa; the remainder are in South America with a few having made their way into Central America, Mexico and southern Texas no later than 5 million years ago. The taxonomy of the characids is still changing and will continue to do so for many years due to increasing study of fish populations. For instance, there are currently some 304 species of aquarium fish in the two genera Hemigrammus and Hyphessobrycon, and all of these are now considered to be incertes sedes [meaning "of uncertain placement"].  Mirande (2009) has proposed a temporary revision of species into clades pending further phylogenetic study; those in Hemigrammus and Hyphessobrycon that have not been assigned to new genera are now deemed in the Hemigrammus clade of Characidae retaining the respective genus names for the present.

For the aquarist, what makes a fish a characid?

  • Externally, many but not all species possess an adipose fin, a small fleshy fin positioned on the dorsal ridge between the dorsal and caudal fins; in some of the pencilfishes this fin may be present or absent within the same species. Other fish groups sometimes have this fin, such as most of the catfishes and the salmonids, neither of which are related to the characins.
  • When a characin is injured, it releases an alarm pheromone called Schreckstoff into the water that triggers an escape response in other members of the species. Other species do not respond to the presence of the pheromones. This chemical warning system may explain their heightened sensitivity to medications and fluctuating water conditions in the aquarium.
  • The presence of a moveable upper jaw confers a feeding advantage to Characiformes. In some species, the jaw is protrusible, enabling the fishes to use suction pressure to capture prey.
  • All characins are egg-layers and except for the species within the Mimagoniates which have internal fertilization, all use external fertilization.
  • But perhaps most importantly, all possess the Weberian apparatus, a modification and fusing of the anterior-most 4-5 vertebrae containing a series of ossicles (movable bony parts) and ligaments that connects the swim bladder to the inner ear. Some other fish groups contain rudimentary signs of this, but in the characids (and other ostariophysians) it is fully developed. This greatly heightens their sense of hearing and may partially account for the characids' instinctive ability to sense danger before it occurs.
All aquarium species of characins are shoaling fish, meaning they live together in groups; this may be for defence against predators, but many species have an interactive social structure within the group. Depending upon the size of the aquarium, most species should be in a group of at least six and preferably eight or more. Keeping these fish individually or in pairs frequently causes significant stress which leads to health problems and a shortened lifespan.  There is also clear scientific evidence of increased or heightened aggression, even within "peaceful" species, when the group is less in size. 

All characins are highly sensitive to water parameters and conditions; the water quality should be stable, and use of medications should be avoided unless absolutely essential. Salt should never be used in an aquarium with characids; with one or two exceptions, all species suffer stress with levels above 100 ppm [= .38 of one gram, or 1/6 of a level teaspoon, per gallon] and many cannot tolerate more than 60 ppm (Weitzman et al., 1996).

Several families within the characids provide suitable aquarium fishes, but there are three that have become very popular with home aquarists. The largest group are the tetra; this common name is an abbreviation of Tetragonopterinae, one of many families of characids but one that ironically is not closely related to most of the tetra species.  The name derives from the Greek tetra (=four), gonia (=angle) and pteron (=wing). The second largest group is the pencilfishes, so called because of their long narrow profile; scientifically these are within the Nannostomini tribe of the subfamily Pyrrhulininae in the family Lebiasinidae. Third are the hatchetfishes, so named from their distinctive hatchet-shape keel, scientifically in the Gasteropelicidae family. Specific traits of these fishes are included in their respective profile.

References:

Mirande, J. Marcos (2009), "Weighted parsimony phylogeny of the family Characidae (Teleostei: Characiformes)," Cladistics Volume 25, No. 6 (July 2009).

Nelson, Joseph S. (2006), Fishes of the World, 4th edition.

Weitzman, Stanley, Lisa Palmer, John R. Burns and Naercio A. Menezes (1996), "Breeding and Rearing Mimagoniates Species, Internally Fertilized Tetras," Tropical Fish Hobbyist Vol. 44, No. 12 (August 1996). 

Banded Leporinus
(Leporinus fasciatus)
Barred Pencilfish
(Nannostomus espei)
Black Darter Tetra
(Poecilocharax weitzmani)
Black Neon Tetra
(Hyphessobrycon herbertaxelrodi)
Black Phantom Tetra
(Hyphessobrycon megalopterus)
Black Widow Tetra
(Gymnocorymbus ternetzi)
Black-Winged Hatchetfish
(Carnegiella marthae )
Blackbanded Pyrrhulina
(Copella nigrofasciata)
Bleeding Heart Tetra
(Hyphessobrycon erythrostigma)
Blind Cave Tetra
(Astyanax mexicanus)
Bloodfin Tetra
(Aphyocharax anisitsi)
Brilliant Rummy Nose Tetra
(Hemigrammus bleheri)
Buenos Aires Tetra
(Hyphessobrycon anisitsi)
Cardinal Tetra
(Paracheirodon axelrodi)
Cochu
(Boehlkea fredcochui)
Colombian Tetra
(Hyphessobrycon columbianus)
Congo Tetra
(Phenacogrammus interruptus)
Coral Red Pencilfish
(Nannostomus mortenthaleri)
Costello or January Tetra
(Hemigrammus hyanuary)
Darter Characin
(Characidium fasciatum)
Dawn Tetra
(Aphyocharax paraguayensis)
Diamond Tetra
(Moenkhausia pittieri)
Diptail Pencilfish
(Nannostomus eques)
Dwarf Hatchetfish
(Carnegiella schereri)
Dwarf Pencilfish
(Nannostomus marginatus)
Eleanor's Pyrrhulina
(Pyrrhulina eleanorae)
Ember Tetra
(Hyphessobrycon amandae)
Emperor Tetra
(Nematobrycon palmeri)
False Penguin Tetra
(Thayeria boehlkei)
False Rummy Nose Tetra
(Petitella georgiae)
Flame Tetra
(Hyphessobrycon flammeus)
Glowlight Tetra
(Hemigrammus erythrozonus)
Golden Pencilfish
(Nannostomus beckfordi)
Golden Tetra
(Hemigrammus rodwayi)
Green Neon Tetra
(Paracheirodon simulans)
Harrisons Pencilfish
(Nannostomus harrisoni)
Head and Tail Light Tetra
(Hemigrammus ocellifer)
Kerri Tetra
(Inpaichthys kerri)
Lemon Tetra
(Hyphessobrycon pulchripinnis)
Loreto Tetra
(Hyphessobrycon loretoensis)
Marble Hatchetfish
(Carnegiella strigata)
Neon Tetra
(Paracheirodon innesi)
One Lined Pencilfish
(Nannostomus unifasciatus)
Penguin Tetra
(Thayeria obliqua)
Pretty Tetra
(Hemigrammus pulcher)
Pristella Tetra
(Pristella maxillaris)
Purple Dwarf Pencilfish
(Nannostomus rubrocaudatus)
Purple Tetra
(Hyphessobrycon metae)
Pygmy Hatchetfish
(Carnegiella myersi)
Rainbow Emperor Tetra
(Nematobrycon lacortei)
Red Eye Tetra
(Moenkhausia sanctaefilomenae)
Red Phantom Tetra
(Hyphessobrycon sweglesi)
Roberts Tetra
(Hyphessobrycon bentosi)
Rosy Tetra
(Hyphessobrycon rosaceus)
Serpae Tetra
(Hyphessobrycon eques)
Silver Dollar
(Metynnis hypsauchen)
Silver Hatchetfish
(Gasteropelecus sternicla)
Silvertip Tetra
(Hasemania nana)
Splashing Tetra
(Copella arnoldi)
Spotted Headstander
(Chilodus punctatus)
Neon Tetra

Lemon Tetra

Black Widow Tetra

Marble Hatchetfish

Serpae Tetra


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