Tequila splitfin (Zoogoneticus tequila)
|Also known as:||crescent goodeid, crescent splitfin, Tequila goodeid, tiro de Tequila|
|Size||Total length: up to 8 cm (2)|
The Tequila splitfin is classified as Critically Endangered (CR) on the IUCN Red List (1).
Previously believed to be extinct in the wild, the Tequila splitfin (Zoogoneticus tequila), named after the Tequila Volcano to the north of its range (3), was rediscovered in a single, tiny pool during surveys in 2000 to 2001 (4).
A small fish with a relatively deep body (3), the Tequila splitfin is characterised by the broad, crescent-shaped, orange-red band on the caudal fin of the adult male, beyond which the edge of the fin is transparent. Adult males also possess narrow, cream-coloured bands along the edges of the dorsal fin, anal fin and sometimes also the pelvic fins (3) (5). The rest of the body is dark olive in colour, fading to pale yellow below, and with some iridescence to the scales. The sides have some mottling, often with a greenish tinge, and there is usually a pair of spots, which often join, at the base of the caudal fin (3). These two features may, however, not be visible when the male Tequila splitfin is in breeding condition and engaged in aggressive male-male encounters, when the body is at its darkest (3) (6). The pectoral fins lack pigmentation (3).
The female Tequila splitfin is usually slightly larger than the male, and can be distinguished by the lack of cream-coloured edges to the fins. Larger females may occasionally show a thin orange-red tail band, but it is less vivid than in the male. Juveniles are much lighter than adults, but have more distinct mottling (3).
The Tequila splitfin can be distinguished from its close relative, Zoogoneticus quitzeoensis, by the male’s orange-red tail band, the pale cream rather than bright orange spots on the edge of the dorsal and anal fins, and the lack of a stripe on the sides of the snout and the body (3) (5) (6).
The Tequila splitfin is endemic to the Rio Teuchitlán, an upper tributary of the Rio Ameca drainage in Jalisco, Mexico (1) (3) (5). However, it is now confined to a single, tiny pool (4) (5).
This species originally inhabited the quieter parts of the river, at an elevation of around 1,300 metres, and was usually found at depths of less than 1 metre. The river expanded into a shallow, open, lake-like habitat, and the bottom was mostly mud, with some sand and rocks (1) (3).
The only known surviving wild population of the Tequila splitfin now inhabits a single, spring-fed pool, which measures 4 metres in diameter, with an average depth of just 20 centimetres. The water in the pool is high in oxygen but low in nutrients, lacks submerged vegetation, and the bottom is lined with pebbles and sediment (5).
Relatively little is known about the biology of the Tequila splitfin in the wild (1). As in other members of the Goodeidae family, the young hatch inside the female’s ovary, and receive nutrients from the female via unique, ribbon-like structures known as ‘trophotaeniae’ (3) (5). After a gestation period of 6 to 8 weeks, the female Tequila splitfin then gives birth to between 10 and 29 live young (3) (5), although most females have fewer than 10 offspring in the first year (3).
Breeding is thought to occur continuously during the summer months (3), although wild females have also been found carrying developing young during winter (5).
The young Tequila splitfins may reach sexual maturity after 6 to 10 weeks (3) (5), or perhaps slightly later in the wild, where temperatures may be lower (3). As in all adult male goodeid fish, the front of the anal fin of the male Tequila splitfin is modified, with the first few rays partly separated from the rest of the fin. This modification, which gives rise to the name ‘splitfin’, facilitates mating (3).
The Tequila splitfin was first collected in 1990 (3), but collection efforts after 1992 were unsuccessful, leading to the belief that the species had become extinct in the wild (1) (3) (4).
The loss of the Tequila splitfin from most of the Teuchitlán River is likely to have resulted from a combination of habitat degradation, intensive collection for the aquarium trade, and the introduction of exotic fish species. The building of a dam has degraded the river, confining many endemic fish to small areas in springs near its headwaters, while the turning of these springs into spas has further fragmented populations by preventing the movement of fish between pools (1) (3) (4) (5). At the time of this species’ discovery, the river water was also reported to be turbid due to disturbance by livestock, to be polluted, and to be heavily utilised for irrigation, drinking and washing (3).
Despite its subsequent rediscovery, the Tequila splitfin is still highly vulnerable in the wild, with a tiny population (possibly fewer than 50 mature adults), confined to a single, small pool, which is under threat from pollution and water extraction (1) (4) (5). It has also recently been found to share its restricted habitat with the invasive Trinidadian guppy (Poecilia reticulata) and the more aggressive Heterandria bimaculata, which could present further threats to this species (6).
The Tequila splitfin is kept in captivity by aquarists in various countries (1) (3) (7), and a breeding programme has been recommended so that the species can be re-introduced into the original, larger pools it once inhabited (1) (5). Measures to protect the remaining wild population have also been recommended, together with a ban on all trade in wild specimens, and strict regulation of traffic with aquarium stocks (4) (5).
The conservation and recovery of this rare fish will also depend on the restoration of its habitat, monitoring of water quality and the management of its populations to minimise inbreeding (4) (7).
Although both wild and captive populations of the Tequila splitfin show low genetic diversity, the wild population may have adapted to its local environment and so any breeding of wild with captive individuals, while it may increase genetic diversity, should be considered carefully as it may potentially affect these local adaptations (7).
For more information on goodeid fish and their conservation see:
Haus des Meeres - Goodeiden Project:
Zoological Society of London (ZSL) - Fish Net:
Authenticated (07/10/11) by Constantino Macías Garcia, Departmento de Ecología Evolutiva, Instituto de Ecología, UNAM.
- Anal fin: in fish, an unpaired fin on the under surface of a fish, behind the anus.
- Caudal fin: the tail fin of a fish.
- Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Genetic diversity: the variety of genes within a particular species, population or breed causing differences in morphology, physiology and behaviour.
- Gestation: the state of being pregnant; the period from conception to birth.
- Inbreeding: the breeding of closely related individuals. An inbred population usually has less genetic variability and this is generally disadvantageous for its long-term survival and success.
- Ovary: the female reproductive organ that produces ova, or eggs.
- Pectoral fins: in fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.
- Pelvic fins: in fish, the pair of fins found on the underside of the body.
IUCN Red List (June, 2010)
FishBase (June, 2010)
- Webb, S.A. and Miller, R.R. (1998) Zoogoneticus tequila, a new goodeid fish (Cyprinodontiformes) from the Ameca drainage of Mexico, and a rediagnosis of the genus. Occasional Papers of the Museum of Zoology, University of Michigan, 725: 1-23.
- De La Vega-Salazar, M.Y., Avila-Luna, E. and Marcías-Garcia, C. (2003) Ecological evaluation of local extinction: the case of two genera of endemic Mexican fish, Zoogoneticus and Skiffia. Biodiversity and Conservation¸ 12: 2043-2056.
- De La Vega-Salazar, M.Y., Avila-Luna, E.G. and Marcías-Garcia, C. (2003) Threatened fishes of the world: Zoogoneticus tequila Webb & Miller 1998 (Goodeidae). Environmental Biology of Fishes, 68: 14.
- Macías Garcia, C. (October, 2011) Pers. comm.
- Bailey, N.W., Macías Garcia, C. and Ritchie, M.G. (2007) Beyond the point of no return? A comparison of genetic diversity in captive and wild populations of two nearly extinct species of Goodeid fish reveals that one is inbred in the wild. Heredity, 98: 360-367.