The Genetic Stock Center provides fish from more than 70 genetic strains to scientists and aquarists around the world. Scientists in more than 30 laboratories in the United States, Canada, Mexico, Japan and Germany work on Xiphophorus genetics and depend on strains available from the stock center. In addition to supplying strains and consultation on husbandry and genetic questions, the stock center makes custom hybrids for a variety of projects, producing hundreds of such fish each year at very affordable costs. Unlike most mammals, where fertile hybrids between species are difficult or often impossible to produce, Xiphophorus hybrids are almost always fertile and are extremely valuable for their genetic variability and their very specific susceptibilities for many different cancers. Extensive use of these hybrids for gene mapping has made the Xiphophorus gene map the fifth-largest among vertebrates, exceeded only by maps of man, mouse, rat and cow in numbers of genes assigned.
The beauty of many Xiphophorus strains has attracted tropical fish fanciers for decades. The demand among cognoscenti for extraordinary fish like X. montezumae, with a sword longer than its body, far exceeds the production capabilities of the stock center, but surplus fish are made available to aquarists when possible. The present stock center facilities hold some 1,200 aquaria, balanced between 900 tanks for genetic stock perpetuation and 300 for hybrids for research projects. While this number may seem large, each new species or newly identified genetic strain necessitates some redesign of the overall management plan.
Quality control at the stock center must be impeccable to maintain integrity of the large numbers of genetic strains (even fish manage to escape, and a "jumper" can mean disaster). Most strains have been purposely bred to carry diagnostic morphological traits such as red and black pigment patterns. Each strain possesses a unique genetic "signature" which can be checked for assurance of stock purity. Individual broods are never mixed, and males and females are separated prior to sexual maturity. All parents of broods are preserved for later reference in the event of later questions. All these precautions take a great deal of time, but have been essential in maintaining stock integrity sometimes more than 50 years.