Mexico

Despite often being referred to as extinct in the wild this monotypic species is still surviving at a few localities. It's not particularly scarce in the hobby with strong captive populations existing, some of which have been selectively bred to produce variations in colour and patterning. As with other goodeids, there is less of a size difference between the sexes than in many other livebearers. This is thought to be related to the relatively primitive...

This species is not recommended to those lacking the facilities to house it for life. Sadly it's all too often seen for sale as an attractive, silvery 2-3" juvenile, supposedly suitable for the general freshwater community tank. To make matters worse, it is also usually given an 'alluring' name such as 'black-finned' or 'silvertip' shark catfish. The fate of the majority of these specimens is in all likelihood a depressing one.

While the surface-dwelling form of this species is fairly unremarkable and rarely-seen in the hobby, the blind form is very popular indeed. The two may have diverged as recently as within the last 10,000 years, with the blind form losing its eyes and much of its pigment. This probably happened because the fish needed better development in other sensory areas. Losing unnecessary and energy-consuming aspects of its physiology allowed it to devote more energy to developments such as increased numbers of taste receptors on the head.

Restricted to a series of small habitats below the waterfall known as 'El Salto' in the upper Río Mezquital basin, Durango state, central Mexico. It was previously considered to occur throughout much of the upper Río Mezquital in both Durango and Coahuila states, but genetic analyses suggest otherwise and have resulted in taxonomic confusion (see 'Notes').

Endemic to a handful of natural springs in the Río Verde valley, San Luis Potosí state, Central Mexico. The valley is believed to have once been filled by a large lake and the relict springs are part of the elevated Río (river) Verde basin which later drains into the much larger Río Pánuco system. Much of the aquatic fauna found in the valley is endemic to the area but in many cases threatened by introduced species.

The type locality originally consisted of a single spring-fed pond located in an endorheic basin known as 'La Hediondilla' at the foot of the 'Cerro Potosí' mountain and around 1880 m AMSL. It had been modified to make it larger via an earth and rock dam, and below the pond were several distributaries running for a distance of 1-1.5 km.

A bright blue variant normally referred to as 'electric blue Jack Dempsey' or simply 'EBJD' is of unclear origin but it appears to be an ornamental strain fixed from a natural mutation. Care is as per the natural form although the blue fish tend to remain smaller and some reports suggest them to be less aggressive. R. octofasciata has a confusing taxono...

This species has been a popular aquarium fish for a considerable period and virtually all fish traded are now raised commercially for the purpose. It is easily identified by the characteristic bright red or orange underside of the head, which is more pronounced in adults. Following Miller and Taylor (1984), the genus Thorichthys is identified...

Wild swordtails are a fairly basic green colur. However the vast majority of swordtails available in the hobby today are hybrids of X.helleri with X.maculatus or X.variatus. There are a huge number of selectively-bred varieties available, including wagtail, lyretail, tuxedo, albino, neon, red, green and hi-fin. Swordtails may undergo what appears to be a change in sex. In young fish this may simply be late development. However some adult females develop male characteristics which is thought ...

A single male of the Tequila Splitfin was sampled in 1955 by Miller and Greenbank, but identified erroneously as Zoogoneticus quitzeoensis, with which species it was collected and found sympatrically . Many years later, the mistake was detected, the fish identified as a new species and finally, 43 years after the first capture, described by Webb and Miller. In 2001, a wild population of this species was rediscovered in a very small spring pool (3 x 4m in diameter). The population there was composed of only a handful of adult fish and a few tens of juveniles (De la Vega-Salazar et al., 2003). In 2007, N. W. Bailey et al showed, that the allelic richness of this population (though it was comparable in size to an aquatic stock) was higher than in any aquatic stock. In 2013 the loss of this population was reported (pers. comm. Domínguez), so there is not much hope that this species is still persisting in the wild.

This is one of the largest freshwater fish species in the world, and clearly shouldn't be considered a home aquarium subject at all given its eventual size and the fact it can live for well in excess of 50 years. We include it here only because some public aquaria are able to maintain it long-term. Unfortunately, juveniles are seen for sale quite regularly in the aquari...

Found in both Caribbean and Pacific-slope drainage basins in Central America, from southern Mexico through Belize, Guatemala, Honduras and Nicaragua, and into Costa Rica. This species clearly shouldn't be considered a home aquarium subject at all given its eventual size and the fact it can live for several decades.

Despite being a wholly unsuitable aquarium subject, C. idella is often traded as such, with an albino form having been developed specifically for the ornamental market. Individuals which have outgrown their aquarium or pond should never be released into natural waters, either, since this species has proven capable of causing serious environmental damage under a wide range of climatic conditions.

H. compressus is the type species of the genus Hyphessobrycon but is not well-known in the ornamental trade. Hyphessobrycon was raised by Durbin in Eigenmann (1908) as a subgenus of Hemigrammus, differing from the latter by the absence of scales on the caudal-fin.

Known from Great Lakes Erie and Michigan with distribution extending south through the Mississippi River basin to the Gulf of Mexico drainages where it's said to occur between the lower Apalachicola River in Florida and the Nueces River in Texas. It may also be found in the Rio Grande which forms the border between Mexico and the United States further south where records include Falcon International Reservoir, for example.

Need not be too complicated so long as there are plenty of broken lines-of-sight. Provide plenty of cover in the form of aquatic plants, wool mops, etc., and if using filtration air-powered, sponge-type units are best as these will not harm eggs or fry. Lighting is unimportant but can be use...

Tends to be most common in brackish to hypersaline environments such as coastal salt marshes, lagoons and estuaries. On San Salvador Island, Bahamas, it appears to be the parent of a species group occurring in sympatry and exploiting diverse but specific resources with some spectacular morphological adaptations.

The surrounding area is semi-arid and the Bolsón de Sandia was once a beautiful oasis with a number of springs, abundant vegetation and diverse wildlife but has dried up over the last twenty to thirty years due to indiscriminate water extraction for agriculture and other human uses. Three endemic species of Cyprinodon, namely C. veronicae, C. longidorsalis and C. ceciliae, have been described from separate springs within the system...

El Pandeño de los Pando has a surface area of around 287 m² with depth ranging from 40-80 cm but there is an abandoned artificial channel which has an area of approximately 437 m². Water temperature fluctuates between 38-48°C/100.4-118.4°F and the spring is considered one of the hottest environments inhabited by fish in the world.