Xiphophorus nigrensis

Xiphophorus nigrensis Rosen, 1960

Affiliation: northern swordtail

IUCN status: data deficient

Distribution: upper parts of Río Choy in Río Panuco basin, San Luis Potosí, Mexico

Known locations (existing/former): 2/2 (Nacimiento and more downstream near Hotel Taninul)

Type locality: Nacimento del Río Choy, 4 km north of Hotel Taninul, 3 km north from Road 110 (Valles-Tampico)
(19.1.1957, D. E. Rosen, M. S. Gordon & M. Gordon)

Habitat description: This species inhabits clear water with strong currents and rocky bottom, with depths reaching up to 3 meters.

Biotope reports:

• none yet

Description: Males of Xiphophorus nigrensis are characterized by their deep bodies and moderately developed swords (in larger males). Larger males usually display iridescent blue coloration on their sides, while smaller males are more slender and often golden. The species exhibits a distinctive zigzag lateral line, and the dorsal fin typically features a black edge. Females have a more robust body with a similar zigzag lateral line, but display a more subdued coloration, typically grayish or brownish with clear fins.

Variability: Populations of X. nigrensis include both large (up to 40 mm) and small adult males (down to 18 mm). Small males are slender, while larger males develop more pronounced swords. Blue and yellow males are present and there is also some variability in back patterns at the caudal peduncle. The variability is similar to X. multilineatus.

XWG status: not yet actively managed

Represented in aquaria: X. nigrensis is less commonly represented in aquaria compared to other Xiphophorus species, but it can be found among specialized breeders.

Known issues: Needs cool temperatures and pristine water. Can be rather shy.

Known collections or populations:

• Río Choy, San Luis Potosí, Mexico

Remarks: The location of this species (Río Choy) is not to be mistaken with Río Coy, inhabited by very similar species, Xiphophorus multilineatus.

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