| Paracheirodon | |
|---|---|
| |
| Paracheirodon axelrodi, a type of neon tetra | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Characidae |
| Tribe: | Pristellini |
| Genus: | Paracheirodon Géry, 1960 |
Neon tetra (Paracheirodon) is a genus of freshwater fish in the family Characidae of the order Characiformes. All species of this genus are native to the Neotropic ecozone, occurring in the Orinoco and Amazon Basins in northern South America.
Neon tetras commonly reach the lengths of 2 to 2.5 cm (0.79 to 0.98 in) and are of elongated, tetra shapes. All share a distinctive iridescent blue lateral line, hence their common name "neon tetras", but differ slightly in their other colorations.
Preferring soft, acidic waters, these midwater shoaling fishes feed predominantly on small crustaceans, insects, worms, and zooplankton. When spawning, they scatter their eggs and guard neither eggs nor young.
A significant proportion of the fish available in the aquarium trade are still wild caught or derive from community-led breeding projects in the middle Negro region, where this species is the most important ornamental fish and in the municipality for as much as about 50% of annual income.
Species edit
There are three species. The currently recognized species in this genus are:
| Species of Paracheirodon | |||
|---|---|---|---|
| Binomial and common names | Image | Description | Range |
| Paracheirodon axelrodi (L. P. Schultz, 1956) |
|
Upper Orinoco and Negro River basins in South America. | |
| Paracheirodon innesi (G. S. Myers, 1936) | 
|
Blackwater and clearwater stream tributaries of the Solimões River in South America. | |
| Paracheirodon simulans (Géry, 1963) | 
|
Upper Orinoco and Negro River basins in South America. | |
Cladogram edit
| Neon tetras (genus Paracheirodon) |
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Varieties edit
One of the most popular and instantly recognizable fishes in the aquarium hobby, this species has been commercially selectively bred on large scale (extensively) to produce a number of ornamental strains including albino, "golden" (leucistic), short-bodied, long-finned, and diamond (in which the dorsal surface is covered with reflective scales).
As in all members of the genus, some wild specimens possess a variable number of golden metallic scales and are marketed as platinum or gold. Although naturally-occurring the condition is said to be caused by a parasite which stimulates increased guanine deposition in the scales.
Neon tetras are highly variable, there are differences in color patterns; some forms possess a straighter and longer neon stripe which terminates below the adipose fin base, some has the red pigment extending slightly further onto the belly, some have less red pigmentation in the ventral portion of the body, some have their neon stripes end before the adipose fin, and some have slightly curved neon stripes in a slight arc shape.
Diseases edit
Unfortunately, years of commercial breeding have somewhat affected the genetic vigor of the ornamental strains meaning morphological defects and ill-health are widespread and care must be taken when selecting a stock. Neon tetras are also susceptible to an ailment commonly referred to as "neon tetra disease" (NTD). It’s therefore recommended to spend time observing the fishes in the shop and if any are displaying signs of restlessness, white patches on the skin or setting themselves apart from the main school, all classic signs of the disease, it’s best to avoid purchase entirely. NTD is caused by a microsporidian parasite called Pleistophora hyphessobryconis and is virtually untreatable once it reaches an advanced stage. The spores (larval stage) of the parasite enter the fish through the mouth and burrow through the walls of the gut before settling in the muscles. Here they produce cysts which cause rapid degeneration of the muscle tissue and development of the characteristic white patches. Once the disease becomes established the rate of mortality can be very high and the only way to treat the aquarium is by physically removing any fish exhibiting signs of infection. Similar symptoms may be observed in a common illness caused by the pathogenic bacteria Flavobacterium columnare, which is often referred to as "columnaris" or "false neon tetra disease" and can be successfully treated using antibacterial products, meaning it’s always worth isolating and treating a fish showing symptoms of NTD as you may be able to cure it if the bacteria is to blame.
Taxonomic notes edit
The taxonomic history of all three species is complicated with earlier authors such as Géry (1960, 1977) tending to include them in separate genera as Hypessobrycon simulans, Cheirodon axelrodi and Paracheirodon innesi, respectively, with this classification mostly based on dental morphology following the system proposed by Eigenmann (1915). Others such as Madsen (1975) placed both P. axelrodi and P. simulans in the genus Cheirodon while van Ramshorst (1981) included P. innesi in Cheirodon as well.
Weitzman and Fink (1983) provided the first evidence for the monophyly of Paracheirodon, containing all three species, via a number of osteological characters plus their distinctive color pattern consisting of an intense blue or blue-green lateral stripe, dense red pigment on the body restricted to the portion ventral to the lateral stripe, and a stripe of dark brown or black chromatophores underlying and extending dorsally to the lateral stripe.
A fourth neon tetra species was discovered by Heiko Bleher in 2006 at a single locality, a nameless igarape within the Rio Purus system, the main channel of which enters the Amazon upstream of the Rio Negro. The fish has to date not been described, but DNA sequencing by Axel Meyer on the few specimens recovered apparently indicates that the newly discovered species is genetically closest to P. innesi (Bleher, 2008).
The close relationships of Paracheirodon within the family Characidae have not yet been fully-confirmed with the grouping considered incertae sedis by the majority of recent authors.
Results obtained in the molecular phylogenetic analysis of Oliveira et al. (2011) recovered P. axelrodi to be most closely related to certain members of Hyphessobrycon species (specifically H. eques and H. megalopterus) among those species included in the study.
The function of the intense blue lateral stripe in Paracheirodon spp. may have evolved as a predator evasion strategy according to the hypothesis of Ikeda and Kohshima (2009) which was published following direct field study of the fish in blackwater streams near Requena in the Peruvian Amazon plus observation of wild specimens in aquaria under different conditions.
The researchers found that the bright coloration of the lateral stripe in P. innesi is less conspicuous in blackwater except when viewed from a limited angle of around 30° above the horizon, and that this could aid in confusing predators via bright mirror images of the stripe being projected onto the underside of the water surface.
Whereas most characids displaying a laterally-striped color pattern possess a dark-colored lateral stripe with a lighter stripe dorsally, this pattern is reversed in Paracheirodon and may be an adaptation for forming such mirror images.
The fish are also able to change the intensity of their overall color pattern to an extent, becoming lighter in bright conditions with pale substrate or background and clear water, and duller with a violet lateral stripe at night, and this may also be a response designed to make them less visible.
Species identification edit
P. axelrodi is the largest among the genus and the basal species in genus as results obtained in the molecular phylogenetic analysis that it is the most closely related to the certain members of Hyphessobrycon species (specifically H. eques and H. megalopterus) among the neon tetras and obviously has the reddest pigment which covers the whole part below the lateral stripe and having broadest and bluest lateral stripe. P. innesi possesses red pigment on the body occurring only half the body and having the narrowest lateral stripe. P. simulans is the smallest among the neon tetras and having the greenest (lightest) lateral stripe, its red pigment is between P. axelrodi and P. innesi and is greatly reduced and is exceptional, its stripe extends to the base of the caudal fin instead stopping little posteriorly unlike P. axelrodi and P. innesi.