XGSC Stocks

This stock of X. alvarezi, Dolores, was derived from fish collected by Donn Rosen, in the late 1960’s and early 1970’s. This stock is maintained as an inbred line. The Dolores stock is found naturally in the Rio Dolores system. The males are characterized by a bright red flush below the lateral line, extending from the operculum to the caudal fin. Males carry a Y-linked gene for orange sword color. Females also carry this gene, but do not express the trait.

X. andersi was first described by two German collectors in 1980. The progenitors of the X. andersi maintained at the Stock Center were collected in 1981 from the Rio Atoyac in Veracruz, Mexico. This species has a limited distribution, and is restricted to the headwaters of the Rio Atoyac, making it a species of special concern. Dr. Klaus Kallman established two strains for size differences in this species: one strain was established using parents with the genotype for small size (andB), the other, from parents with a genotype for large size (andC). This size difference has been attributed to a gene that controls the age of sexual maturation, a Y-linked pituitary factor (P-factor). Two alleles segregate at this locus in the stock: one allele for early maturation, hence, small size, and a second, for late maturation and large size. Males of the andB strain mature at an earlier age than males of the andC strain, and therefore, are smaller than males of the andC stock. A second difference between the two stocks is the presence or absence of a pseudogravidity spot. Males of the andC strain display this spot, while males of the andB strain have a dominant, Y-linked suppressor gene that prevents expression of the pseudogravidity spot.

This stock arrived at the Stock Center from Dr. Manfred Schartl’s Lab in Wurzburg, Germany on July 3, 2001. The line was originally collected from Rio Axtlapezco, Mexico, in March of 2000. The fish express the macromelanophore pattern termed carbomaculatus (Cam) which is also seen in X. cortezi. Cam consists of large, black pigment cells generally located on the body and may extend into the dorsal fin.

Representatives of the FincaII stock of X. clemenciae were originally collected from the San Carlos type-location in Oaxaca, Mexico by Dominic Isla and his wife Janet Ruli. These wild caught fish were sent to the Stock Center on November 15, 2000. The fish currently in the Stock Center are descended from these wild caught females.

Representatives of the Grande stock of X. clemenciae were collected from the Rio Grande in Veracruz, Mexico by Klaus Kallman in 1993. The fish currently in the Stock Center are descended from wild caught females.

Six females and five males of the contiIII stock arrived at the Stock Center on January 16, 2003. These fish originated from Dr. Mike Ryan’s Lab at the University of Texas in Austin. There are no segregating phenotypes in this stock.

This species displays a single zigzag, horizontal stripe; and especially in some males, long, narrow vertical bars appear along the flanks. The sword is upturned with dark melanophores along the ventral margin. The grave spot is well developed and anterior to the caudal fin (Rauchenberger et al., 1990).

The X. cortezi stock was introduced into the Stock Center in 1982. Several phenotypes are segregating in this stock. The different phenotypes include two autosomal macromelanophore patterns, atromaculatus (At) and carbomaculatus (Cam). The At pattern is distinguished from Cam by the number, size and general location of the macromelanophores. The At pattern comprises smaller and more numerous spots located on the dorsal fin and dorsal flank of the body, just below the dorsal fin. The spots in the Cam phenotype are less numerous and larger (usually no more than two or three) and are more predominant on parts of the body, but may be present on the dorsal fin as well. The Cam phenotype masks At, therefore, it is important to never mate At fish with Cam fish, (Rauchenberger et al., 1990; Kallman, 1971).

Along with the two autosomal macromelanophore patterns, there is also an autosomal tail pigment pattern, caudal blotch (Cb). This pattern is maintained in a heterozygous state by crossing Cb fish with wild type individuals. There are also two Y-linked pigment patterns: tail-yellow (Ty) and spot-caudal (Sc). Some Sc males have developed melanosis and small melanomas. A P-factor for early maturation is linked to the X-chromosome and one for late maturation on the Y. In natural populations there are also Y-chromosomes with an early P-factor.

Representatives of X. couchianus maintained in the Stock Center were collected in 1961, from Huasteca Canyon, Nuevo Leon, Mexico (Kallman, 1975). As of 1975, this stock had been maintained by inbreeding for 22 generations. This species is extinct in its natural habitat. Currently, the X. couchianus stock is in the 71st generation of inbreeding. Many generations of inbreeding have produced individuals homozyogus at most, if not all, loci.

The X. evelynae arrived from Dr. Manfred Schartl of Germany in 1998. Progenitors of this stock were collected from a lake near Necaxa, Hidalgo, Mexico. This stock displays two spotting patterns, an X-linked speckled-1 (Se-1) and a Y-linked speckled-2 (Se-2). There is also an X-linked wild-type (+) allele. Se-1 fish display a few larger spots, and Se-2 fish display many smaller spots, such that the pattern is often described as ‘salt and pepper’. There is also vertical barring seen predominantly in males, and concentrated toward the middle of fish. Sex determination in this stock is XX/XY.

This stock is one of the three species of Northern platyfish maintained at the Xiphophorus Genetic Stock Center. X. gordoni has the deep lying body spots (albeit poorly developed) characteristic for the Northern platyfish. These deep lying body spots are found in the septae of muscles and in the connective tissue lining the blood vessels, especially in the blood vessel along the lateral line just below the vertebral column (Atz, 1962). The other two species with this pattern currently housed at the Stock Center are X. couchianus and X. meyeri.

X. gordoni is considered endangered due to a narrow and very limited habitat range, in Cuatro Cienegas, Coahuila, Mexico. Therefore, it would be difficult to recollect these from the wild, thus increasing the importance of the stock currently under cultivation.

The albino X. hellerii (HeAlb) was created by Dr. Manfred Shartl. He used an albino platyfish and continually crossed it with his X. hellerii Lancetilla stock while selecting for the albinism, thus generating and essentially pure stock of X. hellerii Lancetilla that is albino. This stock arrived at the Stock Center on July 3, 2001 from Dr. Schartl at the University of Wurzburg, Germany, via Dr. Ingo Schlupp.

The Belize stock was originally collected from the Belize River in Mexico in 1989. The stock has been in the Stock Center since 1993. Males in this stock possess either a bi-colored orange / green sword, or an all green sword. The gene for sword color is Y-linked, with two co-dominant alleles, orange and green, segregating at the locus. The sex determination mechanism for this stock is WY / YY; therefore, both sexes possess a Y chromosome(s) with the gene for sword color, but expression is sex-limited to males.

The BXII strain of X. hellerii is one of the southern swordtails and was originally obtained from the Belize River, Belize, in 1949 by Dr. Myron Gordon and G. Fairweather. Since 1955 this stock was maintained by Curt Kosswig until 1962 where it was then bred in Dr. Dierk Franck’s laboratory at the Zoologishes Institut, Universitat Hamburg, Germany. Under laboratory conditions inbreeding has been avoided during the perpetuation of this stock. Fish representing the BXII strain arrived at the Stock Center in San Marcos on July 3, 2001. This stock appears to be fixed for a orange sword color and the macromelanophore spotting pattern, dabbed-1 (Db-1) pattern described in 1966 by Kallman & Atz (Zoologica N.Y., 51, 107-135). This pattern Db-1 is coded by an autosomal dominant allele, and appears to show 100% penetrance (Kallman, 1975).

The gene for dabbed-1 (Db-1) is distinct from the gene encoding the dabbed-2 (Db-2) pigment pattern found in the HX strain of X. hellerii. This was demonstrated with crosses between these two stocks. The spots produced with the Db-2 allele in HX form apparent rows, while the spots produced with the Db-1 allele of BXII are more randomly distributed (Kallman & Atz, 1966).

The Cd stock was originally collected in the Rio Jamapa near Cordoba, Veracruz, Mexico. This stock has been maintained in the Stock Center by inbreeding for over 50 generations. Individuals of this strain are characterized by the presence of a dark brown lateral stripe, which extends from the eye to the base of the caudal fin. Cd males possess a yellow / green sword, and also display a brilliantly colored yellow dorsal fin. The gonopodium in males is also yellow.

This new strain of X. hellerii was collected from a small stream named Doce Millas, Rio Junapan drainage, Oaxaca, Mexico. Males express sword coloration as either orange (or) or green (gr). Some males also express an additional red line above the mid-lateral line, which can become much enhanced in older, dominant males. This coloration has been termed rubra litoralis (Rl) and appears to be linked to the green sword color. Preliminary data also indicates that the orange sword color shows complete dominance over the green sword color. Sex determination and pigment inheritance is still being studied in this strain and is yet to be conclusively determined.

Specimens of the HX strain of X. hellerii were collected by Myron Gordon in 1951, from the Rio Lancetilla in Honduras. This stock which was originally bred in the laboratory of Dr. Gordon, exhibited macromelanophore spotting in the flank. This pattern, named dabbed-2 (Db-2), consisted of spots of irregular size and shape that “show a tendency to be arranged in rows”. This arrangement of spots gives the appearance of stripes, and this striping pattern becomes more pronounced with age. Each 'stripe' consists of approximately 8-10 spots (Kallman and Atz, 1966). (Such striping is rare in the BXII strain, where any similar row consists of at most 4 spots.) Results of breeding experiments between HX and BXII strains suggest that these two spotting patterns are controlled by different genes. Further breeding experiments showed that the Db-2 phenotype is controlled by an autosomal dominant gene that shows 100% penetrance.

Another segregating color pattern observed in the HX strain is sword color. According to preliminary Center data this trait appears to be Y linked and sex limited to males. Two alleles are seen at this locus in this population: one expresses an orange color, and the other a green color in the sword. These two alleles are co-dominant. In heterozygotes, orange color appears on the top half of the sword, and green appears on the lower portion of the sword.

Specimens of this stock were first collected in the spring of 1963 from a tributary of the Rio Chachalaca, near the town of Jalapa, Veracruz, Mexico. These fish were maintained as a stock at the Zoological Institute in Hamburg, Germany (Zander, 1967). In June of 1993, the Stock Center received five females and five males, estimated to be about one-year of age, from two different pedigrees. Two phenotypes are represented in males of this stock, black and red. Although sex determination has yet to be established, heritability studies are underway at the Center using these two phenotypes of males.

The history of the HX and Lancetilla strains: Dr. Gordon collected the progenitors of the strain(s) in the Rio Lancetilla, Honduras, 1951. He called this strain “Hx”. “H” stands for Honduras and “x” for Xiphophorus, to wit “Honduras Xiphophorus”. The stock was heterozygous for the macromelanophore pattern Db2. Soon after the fish arrived in his lab in New York, he sent a subset of Hx fish to Dr. Curt Kowsswig in Istanbul. In Turkey he designated the stock “lancetilla.” Eventually the Hx strain died out in New York. Dr. Kosswig returned to Hamburg, Germany, in 1957 and brought the Lancetilla fish with him. During the next 40 years a subset of the Lancetilla stock was disseminated to other laboratories: Dr. Anders, Dr. Schartl and Dr. Schroder. When Dr. Kallman visited Dr. Schroder’s lab in 1993 he returned the Lancetilla fish to New York and reverted the stock back to the “Hx” designation. While the Hx stock and the Stock Center was breeding poorly in the mid 1990’s more of the Lancetilla fish were obtained from Dr. Schartl’s Lab at the University of Wurzburg, Germany in 1996. This stock continues to be termed Lancetilla. While the Lancetilla stock expresses bi-colored swords, these fish do not possess the Db-2 pattern.

The HeLi stock was constructed in Dr. Anders' laboratory by crossing X. variatus Lineatus with X. hellerii Lancetilla (Anders, et al., 1973). This mating produced hybrid progeny displaying the Lineatus (Li) pigment pattern. These fish were then crossed repeatedly into pure Lancetilla fish, until the resulting stock was relatively pure X. hellerii expressing the Li pattern. HeLi is now maintained as a separate X. hellerii stock in the Stock Center. The gene for the Li pattern maps to the X-chromosome, and two alleles segregate at this locus in this captive stock, wild-type (++) and Li.

The Sarabia strain of X. hellerii was collected in 1963 from the Rio Sarabia near Oaxaca, Mexico (Kallman, 1975). A subset of this stock was given to Drs. Siciliano and Morizot in Texas and Dr. Vielkind in Vancouver. The stock was shipped to the Stock Center in early 1993. This strain is marked by a bright red stripe, extending from the eye to the caudal peduncle, and one to two horizontal rows of red spots on the dorsal fin. In the female, yellow spots are located on the ventral portion of the caudal fin, and yellow cells also appear in the anal and pectoral fins. This stock is polymorphic for sword color. Two alleles, orange and green, segregate in the stock, and the green allele is recessive to orange. The gene for sword color is Y-linked (Kazianis, 2005).

About 60 X. maculatus BpII arrived at the Stock Center on August 13, 2003 from Dr. Harry Grier. The fish were originally collected at Kate’s Lagoon in Belize under a collecting permit issued to Craig Watson. A handful of the many varying color patterns represented in the population were chosen to perpetuate the stock. The four main body colorations include Body red (Br), Spotted Dorsal (Sd), iridescent blue (blue), and wild type body (+). Segregation of these color patterns indicates that Br, Sd and + are linked to Y chromosomes in a WY/YY sex determining mechanism. The segregation of the blue phenotype and the Moon (M) tail-spot pattern indicates that these two patterns are inherited autosomally.

Cp is a strain of X. maculatus collected from the Coatzacoalcos drainage basin. Three distinct Y-chromosomes are maintained in this stock (Kallman and Borkoski, 1978; Bao and Kallman, 1982). One Y-chromosome carries an allele for a specific spotting pattern, Sp9 (YSp9), which results in a concentration of black pigment spots on the operculum and along the midline region of the body. This phenotype is limited to platyfish from this drainage. The Sp9 fish are small in size, as this spotting allele is linked to a P-allele (P-1), that results in early maturation, and thus, small size. A second Y-chromosome carries an allele for red anal fin, Ar. In females, this pattern is faintly expressed at 6 to 9 months of age as sparsely arranged, red spots on the proximal portion of the anal fin rays. This phenotype must be scored under a microscope at 10x magnification. The gonopodium appears yellowish in males carrying an Ar allele. Males must also be scored under 10X magnification for Ar. A P-allele for late maturation, P-6, is linked to the Ar allele (YArP-6). Fish carrying this phenotype should be larger in size. The third Y-chromosome carries only the wild type allele for color, i.e., no pigment pattern (Y+). The Cp stock is fixed for the tail-spotting pattern, complete crescent (Cc).

Ancestors of this stock were collected from the Rio Jamapa, Veracruz, Mexico in 1939 by Dr. James W. Atz. This line was established in the early Stock Center in New York with offspring from a single female from that collection. After nine generations, this stock was split into two lines, which have been maintained separately by inbreeding since that time (Kallman, 1968). These two stocks are designated Jp163A and Jp163B. The Jp163A stock at the Stock Center is currently in the 122nd generation of inbreeding. This stock is also used in the production of four (or more) hybrids. Six phenotypic traits are maintained in this stock: four sex-linked traits, and two autosomal traits (Gordon, 1953; Kallman, 1970). The X-chromosome in this stock carries two linked pigment pattern genes: one that produces a red dorsal fin (Dr), and a second that encodes the expression of macromelanophores in the dorsal fin (Sd). Two additional pattern genes are linked on the Y-chromosome: stripe-sided (Sr) and a gene that produces a red anal fin (Ar). The shoulder spot (ss) develops on the anterior, dorsal part of the flank. The shoulder spot trait is determined by two gene loci (lets call them arbitrarily m and n): one sex linked and the other one autosomal. The trait is expressed when the fish is homozygous recessive at both loci. But Belize fish introduced the N allele and the N locus could be demonstrated. This strain is also homozygous for dot (D), a spot displayed on the tail. Two P-alleles exist in this stock. P-1, the earliest p-gene documented in X. maculatus, is linked to the X-chromosome. P-2, the second earliest, is linked to the Y-chromosome.

The Stock Center at San Marcos received Jp163B fish from the New York Aquarium in February, 1993; the fish originally shipped were from the 76th and 77th inbred generations. Currently, the stock housed at the XGSC is in the 113th generation of inbreeding. This stock of X. maculatus is maintained for one X-linked gene, spotted side (Sp), and two Y-linked genes, anal red (Ar), and striped side (Sr). In addition, two autosomally inherited traits, one for shoulder spot (ss) and one for dot (D), are maintained in this stock (Kallman and Atz, 1966). The shoulder spot is expressed only in females, as a gene linked to Sr inhibits the expression of shoulder spot in males. These traits are fixed in this captive stock.

Two P-alleles exist in this stock, the same as with Jp163A. P-1, the earliest p-gene documented in X. maculatus, is linked to the X-chromosome. P-2, the second earliest, is linked to the Y-chromosome.

Ancestors of this stock were collected from the Rio Jamapa, Veracruz, Mexico in 1939 by Dr. James W. Atz. This line was established in the early Stock Center in New York with offspring from a single female from that collection. This was the same collection that originated the Jp163A and Jp163B stocks, this line being originally designated the Jp30 stock. In August of 1999 the last Jp30 female was lost after of 90 generations of inbreeding. So the remaining males were crossed with the Jp163A stock housed at the Center to preserve the well defined chromosomes. The resulting strain designation is Jp30-revisited (Jp30R). Five phenotypic traits are maintained in this stock: four sex-linked traits, and one autosomal tail spot pattern. The X-chromosome in this stock carries two linked pigment pattern genes: one that produces a red dorsal fin (Dr), and a second that encodes the expression of stripped side (Sr). Two additional pattern genes are linked on the Y-chromosome: striped side (Sr) and a gene that produces a red anal fin (Ar). This strain is also homozygous for one-spot (O), a spot displayed on the tail.

This stock has been maintained as a stock separate from the other X. maculatus since it originated from a Belize platyfish stock. The Y-chromosome carries a gene for red body color (Br) which is closely associated with P-4 P-alelle, resulting in late maturation rates in this stock. This stock also exhibits dot (D), shoulder spot (ss), spotted dorsal (Sd) and dorsal red (Dr), all characters derived from X. maculatus Jp163A.

This stock has been maintained as a stock separate from the other X. maculatus since it originated from a Belize platyfish stock. The Y-chromosome carries a gene for red iris color (Ir) which is closely associated with P-3  P-alelle, resulting in intermediate maturation rates in this stock. This stock also exhibits dot (D), shoulder spot (ss), spotted dorsal (Sd) and dorsal red (Dr), all characters derived from X. maculatus Jp163A.

This stock has been maintained as a stock separate from the other X. maculatus since a crossover event occurred in the Belize platyfish. The crossover resulted in the linkage of the genes for iris red (Ir) and body red (Br) on the Y chromosome, and consequently, males of this stock show both patterns. In addition, the ventral margin of the caudal fin is often black in males. This stock also exhibits dot (D), shoulder spot (ss), spotted dorsal (Sd) and dorsal red (Dr), all characters derived from X. maculatus Jp163A. The X-chromosome of this stock carries the early maturing P-1 factor. Preliminary data also indicates that after the Br gene crossed over, the late maturing P-4 factor remains linked.

Nigra is a strain of X. maculatus that carries alleles at two X-linked genes that give rise to the Nigra pigment pattern (N = big black spots) and orange caudal peduncle (Cpo). This chromosome is designated XNCpo. The gene encoding the Nigra pattern is linked to a maturation allele, P-5, which results in the “latest” maturation documented in X. maculatus. Therefore, this strain has very late maturing, large fish (Kallman and Borkoski, 1978). This X chromosome XNCpo originated from a collection of X. maculatus from Belize. The X chromosome was crossed into Jp stock in order to determine maturation rates and inheritance.

This strain originated from the Rio Papaloapan drainage in Veracruz, Mexico. A Y-linked gene causes the expression of a red spot over the anal fin (Arsp) in adult males; this is also known as ruby throat. Genes encoding additional pigment patterns mark two X-chromosomes segregating in this population. One X-chromosome carries an allele at a gene that encodes a yellow iris (Iy). The other X-chromosome carries two linked pigment genes, one affecting dorsal fin color, dorsal red (Dr), and the other spotting on the flank (Sp). This stock also has two alleles segregating at a gene for an autosomal tail-spot pattern, the allelic designation reflecting the number of spots expressed: one spot (O) and twin spot (T).

Both males and females in this stock are homogametic, i.e., the sex chromosomes in both sexes are YY. The Y-chromosome of this stock, which carries the gene for anal red (Ar) and shoulder spot, was derived from Belize platyfish (Bp) and introgressed into the Jp163 stock. The introduction of the Bp Ar gene into the Jamapa genetic background resulted in enhanced expression of Ar. The fish, particularly males, may show expression levels of Ar ranging from the appearance of a red dorsal fin to an entirely red fish. The Ar allele on the Y chromosome is linked to an unidentified P allele, which appears to delay maturation even later than the P-3 allele (about intermediate).

The Jp163B stock of X. maculatus maintained at the New York Aquarium experienced a number of crossover events in the late 1980's as a result of which two genes, spotted side (Sp), and striped side (Sr), became linked on the X-chromosome.

The Up-2 stock was collected in 1963 from the Rio de la Pasion (Rio Usumacinta system), Alta Verapaz, Guatemala. The sex chromosomes, W and Y, segregate in this stock; the W chromosome carries no color pattern alleles. The Y-chromosomes carry two different pigment genes: for iris yellow (Iy) or the macromelanophore spotting pattern #4 (Sp-4). Both color patterns are displayed in males and females. No tail patterns occur in this stock. Females have been documented to display more than one phenotypic color pattern, and dissection revealed that these females contained undifferentiated gonads. This indicates that the females were YY with some secondary sex determining mechanism in effect.

This stock of X. maculatus also originated from the Rio Jamapa drainage, Veracruz, Mexico, and has been under cultivation since 1971. This stock shows two phenotypes for a tail spot pigment pattern, twin spot (T), and crescent (C). Both of these phenotypes can vary in expression and may be difficult to score. The gene(s) encoding these is presumed to be autosomal, but the inheritance of this pattern remains uncertain. This fish also has blue-green iridescence in the shoulder region. No P-genes have been identified in this stock.

The Jp163A stock of X. maculatus maintained at the XGSC in San Marcos produced a cross over female in 1999 who expressed the male phenotype of striped side and anal red (SrAr). This female was mated to create a new strain with the SrAr genes linked to the X-chromosome. This stock is now perpetuated by crossing to the Jp163B stock.

This stock is a product of a crossover event in Jp163A which resulted in linkage of the spotted dorsal (Sd), the dorsal red (Dr) and the shoulder spot factors to the Y-chromosome. This line is maintained by mating a YSdDr male with a Jp163B female; therefore, these males also inherit the X linked gene for spotting, XSp.

This stock of X. maculatus arose from a crossover in Jp163A, resulting in spotted dorsal (Sd) becoming linked to striped side (Sr) on the Y-chromosome. Mating the YSdSr males with Jp163B females allows for maintenance and easy detection of cross-overs.

This stock is a product of a crossover event in Jp163B which resulted in linkage of the spotted side (Sp) to the Y chromosome. This line is maintained by mating a YSp male with a Jp163A female; therefore, these males also inherit the X linked gene for spotted dorsal & dorsal red, XSdDr. P-1, the earliest P-allele, is associated with the Y-Sp chromosome and results in early maturing males.

The Muzquiz platyfish was collected from Melchor Muzquiz, Coahuila, Mexico in 1983. Dr. Schartl shipped the progeny of wild-caught fish to the New York Aquarium in September, 1983. Two lines displaying a difference in melanophore pigmentation were identified, and have been maintained since that time. The spotting pattern is a polygenic species-specific trait. Variation at an autosomal locus controls its presence or absence. A recessive allele acts as a suppressor for spotting. Evidence for this view is provided by the observation that when unspotted X. meyeri are hybridized with unspotted X. maculatus all F1 progeny develop deep lying spots at a somewhat reduced rate. In the back-cross generation to X. maculatus the spotting is highly variable and becomes significantly reduced (Kallman unpubl.). The pattern is caused by deep lying macromelanophores arranged around blood vessels and myoseptae along the flank. The male of this species is heterogametic, XY; the female is homogametic, XX. Fish are sexed at about 1.5 months of age, and become mature at 3 months of age.

X. milleri was described by Rosen (1960), in collections from Catemaco, Veracruz, Mexico. The fish in early collections displayed two macromelanophore patterns, one which showed strictly paternal inheritance, leading Kallman and Atz (1966) to conclude that this species has an XX / XY mechanism of sex determination. In addition, three micromelanophore tail-spot patterns were evident in this species. The X. milleri stock maintained in the Stock Center was collected in 1982. These fish showed two types of striped side patterns: striped side (Sr), which looks similar to the Sr in X. maculatus and is more defined, and faint striped side (Srf), which is more difficult to see. Sr expression masks the presence of Srf. The stock also has a Y-linked allele for black-gonopodium (Gn) and will only be seen in males. There are also two P-factors segregating in this stock, one for early maturation and small size (S), and one for late maturation and large size (L).

The progenitors of this stock were originally collected from the Rio del Sol, on the Isthmus of Tehuantepec in Oaxaca, Mexico, in 1992 by Morizot, Kallman, Borowsky, and Isla. The stock of Sol fish at the XGSC were acquired from Dr. Don Morizot’ Lab at the University of Texas – MDACC on November 22, 2002. This newly described species, like X. clemenciae, lacks a row of spots in the dorsal fin, as found in X. hellerii. The X. clemenciae and X. mixei populations differ, however, in the color of the spots at the base of the caudal fin (red in X. clemenciae, and black in X. mixei), as well as in number (fewer spots are seen in Sol fish). In addition, the sword tapers more rapidly in Sol fish. Males show a reddish coloration, although, it was noted that the father of one of these broods showed no trace of this red coloration (K. Kallman, pers. comm.).

Representatives of this strain were collected in the Cienega Grande, San Luis Potosi, Mexico in 1984 by Kallman and Morizot. A trait showing some variation in the population is the presence or absence of a dark stripe along the lateral line. This stripe is seen in both males and females, but the genetic basis of this is not understood. Males show a basal row of melanophores on the dorsal fin, and random, but numerous melanophores scattered on the dorsal fin. No other melanophore patterns are observed in this population. The stock was initiated in 1984 with a shipment of 29 fish: 12 males with a red stripe (A line), and 17 wild type males (B line). The red stripe is possibly sex-linked (K. Kallman, pers. comm.), although this trait may have been lost in the XGSC population. These fish require large tanks and large amounts of food for healthy development. When more than one male are combined in a single tank, only one will develop a sword, i.e., production of the sword is suppressed in the other males.

Specimens of this strain were collected in 1983 from the Rio Ojo Caliente, San Luis Potosi, Mexico, by Kallman and Morizot. This is a small, short tributary of the Rio Santa Maria, and is just north of the Rio Verde, where Xiphophorus is apparently absent (Rauchenberger et al., 1990). Two rows of melanophores are seen in the dorsal fin of males, a row along the base, and a more irregular row through the center of the fin. However, this pattern may be weakly expressed to absent in some males. No polymorphic pigment patterns are known in this stock.

This strain descended from fish collected near Damian Carmona, north of Rascon, San Luis Potosi, Mexico. These fish were collected from the Rio Ojo Frio in the Rio Gallinas system by Kallman and Morizot in 1983. Representatives of this stock were first shipped to the Stock Center in two stages, in 1992 and 1993. This strain is polymorphic for a macromelanophore pigment pattern, which is controlled by a dominant autosomal allele, M. Unlike other X. montezumae populations, males from the Rascon population do not show distinctive dorsal fin patterns. The first shipment of Rascon fish to the Stock Center arrived on October 21, 1992, and was comprised of two pedigrees with 6 spotted (heterozygous, M+) females and 6 wild type males. The next shipment came on May 12, 1993, and contained two pedigrees with a total of 21 females and 22 males. This shipment contained some fish of each sex that were heterozygous for the M/+ alleles.

The recently described X. monticolus resembles X. clemenciae. One primary character aligning this group with X. clemenciae is the shape of the dorsal fin: it is square in males of both X. clemenciae and X. monticolus fish, in contrast to the more rectangular shape seen in X. hellerii. Like X. clemenciae, these fish are small to moderate in size. Also in common, there are no macromelanophore or tail-spot patterns; the caudal fin shows a convex shape immediately above the sword and has no marginal pigmentation. The sword is orangeish in color, with black lining the upper and lower margins of the sword. The axillary stripe that extends from the base of the pectoral fin past the gonopodium is less distinct in El Tejon males, i.e., it is diffuse and faint, as is a black line between the eye and lips. Differentiating X. monticolus from X. clemenciae is one yellowish, faint stripe that runs from the opercle toward the caudal fin and the presence of black spots at the base of the caudal fin.

This stock arrived at the Stock Center from Dr. Mike Ryan’s Lab in Austin, Texas on January 16, 2003. Males of this stock express a blue body coloration (blue) and mature late and at a large size (L). The tail pattern caudal blotch (Cb) is segregating in this stock also.

Originators of this stock arrived at the Stock Center from Dr. Manfred Schartl’s Lab in Wurzburg, Germany on July 3, 2001. Males of this stock express a blue body coloration (blue) and mature early and at a small size (s).

The El Salto stock originated from a collection at Rio Salto de Agua, San Luis Potosi, Mexico, in 1965. Members of this stock were introduced into the Stock Center in 1992. These fish are characterized by a large dorsal fin and a thick caudal peduncle. The male possesses a relatively small sword when compared to X. montezumae. In addition, this stock carries sex-linked alleles for macromelanophore patterns. El Salto fish also show variation for an autosomal trait, caudal blotch (Cb and +) located at the base of the caudal fin. In addition, males show differences in the timing of sexual maturation: early differentiation (small size, s) or late differentiation (large size, L).

The Ocampo stock originated from a tributary of the Rio Tamesi west of Ocampo, Tamaulipas, Mexico, and was brought to the Stock Center in 1984. There are genes in this stock that control maturation rates (P-factors), linked to the X and Y-chromosomes. An allele for early maturation and small size (S) is found on all X-chromosomes in this stock. All Y-chromosomes carry a P-factor for late maturation and large size (L). The males carrying the Y-linked wild-type allele also carry a single allele at a second Y-linked gene for orange sword color. The Y-chromosome that carries the + allele at the macromelanophore locus also possess a factor that causes orange sword coloration. Y-chromosomes with the factor for early maturation occur in the natural population, but are not represented in this stock.

Specimens of X. nigrensis were collected in a headwater cave of the Rio Choy, San Luis Potosi, Mexico, by Dominic Isla on February 17, 1999, and were received at the Stock Center on September 22, 1999. This stock represents the progeny of a single, wild-caught female. X. nigrensis resembles X. pygmaeus, and was originally classified as a subspecies of X. pygmaeus. Not only is X. nigrensis similar in size and shape, but it shows similar coloration and pigment patterns. Both possess a single, dense mid-lateral stripe, which appears solid at birth, but separates into several lines over time. There are additional coalesced zigzag stripes along the lateral surface that are similar in appearance in both species. A unique character seen in both X. nigrensis and X. multilineatus, but not in any other swordtail species, is that the sword shows allometric growth. Consequently, the sword index is not constant in mature males, unlike other species, where this index is relatively constant. The sword is composed of un-branched rays and is often upturned, and often lacks pigment in the distal dorsal surface of the sword (Kallman and Atz, 1967; Rauchenberger, et al., 1990).

The Xiphophorus pygmaeus pygIII stock was collected in the town of Huichihuyan, Mexico at 21o 28’ 48.1” N 98 o 58’ 0” W by Dr. Michael J. Ryan of the  University of Texas. This collection arrived at the Stock Center on May 18, 2002. The stock contains three male phenotypes; yellow (yel), tail-yellow (Ty) and wild-type (+). Females only express the + phenotype.

The original strain of X. signum was collected in the Rio Chajmaic, Alta Verapaz, Guatemala, in 1963. The 'Ch' strain survived for more than 11 generations of inbreeding, but usually exhibited severely aberrant sex ratios (the first seven matings at the New York Aquarium produced 22 males and 205 females, Kallman and Atz, 1966) and was eventually lost. The current X. signum stock was received from Dr. J. H. Schroder, Munich, on 9/28/93, but was derived from individuals of uncertain history. These fish were probably obtained from aquarist Manfred Meyer, and were probably unrelated to the earlier strain. This strain is a member of the southern swordtail clade and was described as a subspecies of X. hellerii (Rosen and Kallman, 1969; Morizot and Siciliano, 1982). Rosen (1969) elevated signum to specific status, with the most notable character being the presence of a grave spot, a micromelanophore pattern in the caudal fins of males and females. X. signum is not known to have ever successfully hybridized, i.e., produced offspring, with any other Xiphophorus species (Kallman, pers. comm.).

This strain of X. variatus was collected by Dr. Kallman from the Arroyo Encino at Encino, Tamaulipas, Mexico. The arroyo flows into the Rio Sabinas of the Rio Tamesi system. The strain shows the black gonopodium (Gn) macromelanophore pattern as well as the xanthophore/erythrophore patterns dorsal yellow and tail yellow (DyTy) or tail red (DyTr). The black gonopodium trait is linked to the X-chromosome and is sex-limited, thus is only exhibited in mature males.

Although males of this strain develop dorsal yellow (Dy) and tail yellow (Ty) (sometimes called Tail Orange (To)), the inheritance is not well understood since these traits are sex limited to mature males. At least in the Rio Panuco basin (and perhaps elsewhere) all X. variatus males may develop yellow dorsals and either red or yellow caudal fins. Caudal fin pigmentation in the Zarco and Encino populations is autosomally determined. The evidence for this was provided by the observation that when strains with yellow or red caudal fin coloration and differently marked Y chromosomes were crossed with each other, in the F2 generation the marker gene on the Y’s segregated independently from caudal fin coloration (Kallman unpubl.). On the other hand, another X. variatus strain was reported to have these patterns on the sex chromosomes but his evidence is not compelling (Anders et al., 1973).

Progenitors of this strain of X. variatus were collected from the Rio Huichihuayan, San Luis Potosi, Mexico. The Stock Center obtained these fish in 1996 from M. Schartl, who had maintained a stock in Germany. This stock has an X-linked lineatus pigment pattern gene, which is expressed as horizontal stripes on the flank. There is also a vertical barring pattern expressed in some dominant and aged males.

This strain of X. variatus was collected from the Arroyo Zarco locality west of Encino, Tamaulipas, Mexico. The arroyo Zarco joins the arroyo Encino. The locale is described by Richard Borowsky (1984). The strain was kept at New York University, until it was moved to UTMD Anderson Cancer Center by Dr. Steven Kazianis. This strain is one of the few where individuals can develop melanoma in the absence of hybridization. The P-2 pigment pattern can eventually result in progressively larger black blotches as an animal ages. After about 1.5 years of age, these fish can develop external melanotic nodules (Borowsky, 1973; Schartl et al., 1995). Usually, this occurs in animals that are homozygous for P-2.

Progenitors of this stock were collected from a small stream at Santa Engracia, Tamaulipas, Mexico. This site is geographically isolated from San Carlos, the locality of X. xiphidium Sc. This locale is also a short distance from Rio Purificacion, a river inhabited by other populations of X. xiphidium. The X. xiphidium Ps stock is so named in reference to an allele present in this stock that encodes the tail spot pattern, peduncular spot (Ps).

This stock arrived at the Xiphophorus Genetic Stock Center 11/9/98, from M. Schartl's lab in Würzburg, Germany. This stock was collected in the Rio Purificacion, near Barretal, Tamaulipas, Mexico. A pigment pattern, flecked (fl-1), described by Kallman and Atz (1966) is segregating in this stock. The inheritance of the flecked pattern is reported to be to be X-linked in the stock. Three alleles for tail spot patterns are segregating in the stock; crescent (C), wild type (+) and cut crescent (ct).

These fish were collected from a small spring in the Sierra San Carlos, Tamaulipas, Mexico. This stock is fixed for the allele encoding the cut crescent (ct) tail pattern. Two spots comprise this pattern: the more ventral spot appears fainter than a spot located on the dorsal edge of the tail fin. No other color patterns are scored. Occasionally, exophidic, 3-dimensional growths are associated with the tail pattern.