Platyfish are members of the Poeciliidae family. The genus Xiphophorus (etymology from Greek "carrier of the dagger”) is composed of 26 described species of both platyfish and swordtails that are found from northeastern Mexico (Coahuila) as far south as Honduras (2200 km). They are omnivorous and typically range in size from 14 to 45 mm standard length (measured from the tip of the mouth to the base of the tail). They are polymorphic for a large number of pigment patterns including sex-linked macromelanophores (red patterns and bold black markings) and autosomally inherited micromelanophores (tail spot patterns).
These fish are livebearers and typically become sexually mature from 4 months (platyfish) to 12 months of age (swordtails). Females X. maculatus develop a gravidity spot when mature whereas in males, the anal fin modifies into a gonopodium which is used to transfer sperm packets to the female. Females, once impregnated, may store sperm for up to 6 months producing broods every 30 or so days. Brood intervals can vary from 21 to 50 days and brood size may also vary from 1 to 160 babies.
Hybrid strains (i.e., interspecies crosses) of Xiphophorus fishes can produce highly ornamental strains that are popular among many hobbyists. Hybridization can also lead to abnormalities such as spontaneously developed malignant melanoma tumors which were discovered over 75 years ago and have been the focus of numerous research studies since that time. The genetic system of these fish has been well studied making them valuable tools for research investigations among varied scientific disciplines.
Xiphophorus maculatus are small freshwater fish that range from the coastal plains of southern Mexico near Veracruz, eastwards to the small streams of British Honduras that drain the Maya Mountains. Platyfish can be found in streams and drainages as well as in stagnant ponds and shallow temporary pools. They are found in water under dense tree canopies as well as areas that have little to no shade from the sun. Substrate in these locations is typically mud and gravel accompanied by aquatic vegetation. Water temperature for their natural habitat is around 23°C.
Use of Xiphophorus fishes as a research model resulted in establishment of the Xiphophorus Genetic Stock Center (XGSC). The XGSC has operated within the United States since the 1930s providing pedigreed and consistent species, lines and crosses to scientists worldwide (www.xiphophorus.org). The traditional strength of the Xiphophorus model involves the non-biased assessment of genetic inheritance patterns associated with complex (multi-genetic) phenotypes within intact animals. The extreme genetic variability among the 26 Xiphophorus species and capability of producing fertile interspecies hybrids allows chromosomal/marker inheritance to be followed in individual backcross hybrid progeny. Statistical analyses involving hundreds of animals in a cohort can then be used to identify markers linked to any trait of interest, so long as the phenotype can be discerned between two parental lines/species and in the hybrid progeny. Recent development of BAC, transcriptome, and genomic resources continue to enhance the experimental power of this model system. See the sequences and maps link to find a BAC fingerprint map and BAC end sequences for interrogation.
The Xiphophorus Genetic Stock Center is located at: Texas State University, 419 Centennial Hall, 601 University Drive, San Marcos, Texas 78666. The Center as well as the BAC resource were/are supported by: NOAA National Ocean Service (grants NA04-NOS42602002, NA05-NOS4261162, and NA06-NOS4260118); the NIH - National Center for Research Resources (P40-RR17072 and R24-RR024790), and the Mitte Foundation. Questions regarding these resources can be addressed to Dr. Ron Walter.