Xiphophorus hellerii Heckel, 1848

Terán, Guillermo E., Koerber, Stefan, Stazzonelli, Juan Carlos, Aguilera, Gastón & Mirande, J. Marcos, 2022, Any colour you like: new records of ornamental livebearers (Poeciliidae: Cyprinodontiformes) from freshwaters of Argentina., Ichthyological Contributions of PecesCriollos 80, pp. 1-8 : 3-5

Xiphophorus hellerii Heckel, 1848 - first record for Argentina

figs. 10 -14

Examined material: CI-FML 7807 , 4 ex. (1 male, 3 females), 36.1- 40.1 mm SL. Bajo Hondo stream in Parque Guillermina , Salí River basin, Tucumán. 26°49’21”S, 65°15’30”W. Coll.: J.C. Stazzonelli & G. Rodriguez, Sep.2020 .

The specimens collected present the characteristics which are diagnostic of this species: a medium to large swordtail with a long straight caudal appendage in males. Midlateral stripe dusky. Terminal segment of gonopodial ray 3 produced into a crescentshaped hook and blade pointed distally (figs. 14-15). Ray 4a curves strongly backward over the blade at an angle greater than 90°. Distal serrae of ray 4p reduced in size and number and proximal serrae rather slender. Terminal segment of ray 5a produced into a claw, several times larger than the distal serrae of ray 4p (following Rosen & Bailey 1963; Kallman et al. 2004).

Phenotype ‚tuxedo‘ from Tucumán

The specimens obtained in Tucumán all present a black stripe from the head to the caudal peduncle in the inferior half of the body on a red or green ground color. This color pattern is artificial and the result of selective breeding activities towards more colorful strains for the aquarium hobby. Specimens of wild populations of Xiphophorus hellerii from its natural area of distribution (fig. 4) may present black spots, but those are distributed randomly on the body without showing any well-defined pattern (fig. 5). Black patterns in Xiphophorus spp. may result in malignant melanomata and develope to skin cancer.

Before having been introduced as genetically stable strains to ’enrichen‘ the aquarium hobby in 1937, professor Kosswig in 1929 had presented his research on cancer and genetics using Xiphophorus spp. as model organisms ( Gentzsch 2019). Kosswig‘s groundbreaking research with Xiphophorus is still referred to as the ‚Gordon-Kosswig Melanoma System‘ by specialists from this field. The breed from Tucumán represents a phenotype called ’tuxedo‘ in the aquarium hobby. This strain was first presented to the public in 1937 as the result of breeding activities in the German city of Wiesbaden ( Mombour & Breider 1937). Due to this geographical origin both forms, black stripe on red or green body, were then named ‚Wiesbadian strains‘. Animals from these strains apparently have been taken to the US very quickly. Until January 1940 this breed was not only available, but had been reproduced already in sufficient quantities to offer ’red tuxedo black‘ for sale in a price list distributed in the US ( EANI 1940). Poeciliids and other livebearing cyprinodontiform species are of broad interest in a specialized branch of the worldwide aquarium hobby. Many aquarium hobbyists interested in livebearers are organized in specialized societies and clubs globally. As these frequently conduct exhibitions and shows with competitions about the ’best‘ fish, the judges need standardized rules for their evaluation of body form, fins, color etc. ’Tuxedo‘ is defined by the above mentioned black stripe from head to tail in the lower half of the body, while no black shall be visible on the fins ( Gentzsch 2019). The specimens from Tucumán show well defined strains of the red and green bodied varieties of ‘tuxedo‘ ( figs. 10-13 ). That so far no cross-bred specimens presenting red areas on green ground or vice versa have been found could be an indication that this is a relatively young population from a rather recent introduction. The mere presence of ’tuxedo‘ swordtails in the wild is remarkable, as most other introduced populations from e.g. Indonesia (fig. 6; Ghafari & Fitrianti 2020), Morocco (fig. 7; Mabrouki et al. 2020), Iran (male, fig. 8; Esmaeili et al. 2015), the Iguazú river in Brazil ( Larentis et al. 2019), etc. show phenotypes more similar to the wild ’green swordtail‘ Xiphophorus hellerii (fig. 4). Specimens from a population recently found in Turkey ( Kirankaya & Ekmekçi 2021) and a female from Iran (fig. 9; Esmaeili et al. 2015) do not show black patterns, but present orange areas on the body and probably also belong to genetically modified strains bred for the aquarium hobby. The same is to be assumed for animals from Australia which show black rays in the caudal fin ( Maddern et al. 2011).

Figures

fig. 10 Xiphophorus hellerii ‘red tuxedo’, adult male from Parque Guillermina, Tucumán. 26°49’21”S, 65°15’30”W.

fig. 11 Xiphophorus hellerii ‘red tuxedo’, female, Parque Guillermina, Tucumán. 26°49’21”S, 65°15’30”W.

fig. 12 Xiphophorus hellerii ‘green tuxedo’, female, Parque Guillermina, Tucumán. 26°49’21”S, 65°15’30”W.

fig. 13 Xiphophorus hellerii ‘red tuxedo’, adult male from lot CI-FML 7807.