African tetra Alestopetersius brichardi

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Byron

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Most of the tetras we maintain are South American, but there are a few families in Africa, and I came across this beauty in the Characin FB group and thought I'd share it.

For those who like natural history...

Characins include the tetras, hatchetfishes, pencilfishes, and the Crenuchidae (Characidium species). Piranha are characins too. Characins—or more correctly characids—belong to the scientific order Characiformes. The name comes 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 (George Albert) 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; Ortí 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 the characids underwent explosive radiation unlike any other in all the vertebrates except for the marsupials in Australia. The diversification of the cichlid fishes in the African rift lakes during the past 15,000 years 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 24 Families [Fishbase, 2022]. 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 phylogenetic study of fish populations. For instance, there are currently some 304 species of aquarium fish in the Hemigrammus clade which includes all Hemigrammus and Hyphessobrycon species, and nearly all of these are deemed incertes sedes, or of uncertain placement.

Some characin features include:
  • All aquarium species of characins are shoaling fish, meaning they live together in groups; this may be for defense against predators, but many species have an interactive social structure within the group. This need is part of the genetic blueprint of every species. Depending upon the size of the aquarium, most species should be in a group of at least ten, preferably more. Keeping these fish individually or in pairs frequently causes significant stress which leads to health problems and a shortened lifespan.
  • 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.
  • 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 it is fully developed. This greatly heightens their sense of hearing and may account for the characids’ instinctive ability to sense danger before it occurs.
Several families within the characids provide suitable aquarium fishes, but there are three that have become very popular with home aquarists. The largest of these are the tetras; the common name "tetra" comes from one of the families, Tetragonopterinae, which name is derived from the Greek tetra (=four), gonia (=angle) and pteron (=wing). Until quite recently, this family was assumed to include most of the common tetra, but DNA and cladistic studies are now changing this, and none of the popular tetra are actually in this family.

Byron Hosking
April 2010, revised October 2022
 

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I've kept a number of African Characins, and their behaviour is really diverse. Their body shapes, too. Wonderful fish.
It's a shame when people deny how the world once was, because there is so much to be learned when you study these fish, even if you do it for your own pleasure. The fish: killies, Characins, Cichlids and others tell a story that's really wonderful.
 

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