"Xenotoca" eiseni

Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Xenotoca eiseni
Original Description: 

  RUTTER, C. (1896): Notes on Fresh Water Fishes of the Pacific Slope of North America. Proceedings of the California Academy of Sciences (2) 6: pp 245 - 267

Etymology: 

  The species is named for the collector of the types, G. Eisen.

Holotype: 

  Collection-number: Museum of Natural Science - Louisiana State University, Cat. No. LSUM-4999.

  There are 4 specimens deposited with this number, the largest one of 33mm TL, collected by G. Eisen, 1894.

English Name: 
Redtail Splitfin
Mexican Name: 
Mexclapique cola roja
Synonyms: 

Characodon eiseni    Rutter, 1896

Characodon variatus    Regan, 1907

Xenotoca eiseni    Fitzsimons, 1972

Karyotype: 

  The Karyotype describes the number and appearance of chromosomes during the phase of condensation, classified by the position of the centromere (Levan et al., 1964).

The following abbreviations are employed:

 

M = large metacentric chromsome (a result of Robertsonian fusion)

m = small metacentric chromsome (centromere at medium position)

sm = submetacentric chromsome (centromere at submedian position)

smst = submetacentric-subtelocentric chromosome (continous series)

st = subtelocentric chromosome (centromere at subterminal region)

stt = subtelocentric-acrocentric chromosome (continous series)

t = acrocentric chromosome (centromere at terminal region)

 

The Karyotype of "Xenotoca" eiseni, following Uyeno, Miller & Fitzsimons, 1983:

2n = 48    6st/ 42t    

Size: 
The maximum known SL is 75mm (Miller et al, 2005).
Terra typica: 

  The types came from a branch of the Río Grande de Santiago at Tepic in the state of Nayarit.

Status after IUCN: 

  not assessed

Status following other sources: 

  Status: Endangered

  Comments: Declining

Distribution and ESU's: 

  This species is living on the Pacific Slope, to be exact from tributaries to the Río Grande de Santiago near Tepic, state of Nayarit, and in this state also in the ríos Tepic and Compostela. Further as long as further examinations have not been taken, specimens from the ríos Ameca and Ayuquila belong to this species. Fish from the endorheic basins of Magdalena and Etzatlán ("Xenotoca" doadrioi) and from the ríos Tuxpán and Tamazula ("Xenotoca" lyonsi) have been described as distinct species in 2016.

 

  ESU ist short for Evolutionarily Significant Unit. Each unit expresses an isolated population with different genetic characteristics within one species.  ESU's can be defined by Molecular genetics, Morphology and/or Zoogeography and help in indicating different phylogenetic lineages within a species. The abbreviation for an ESU is composed of the first 3 letters of the genus, followed by the first 2 letters of the species name and an ongoing number in each species.

 

  In "Xenotoca" eiseni - with respects to the population from the Río Ameca - we distinguish by now three ESU's: Xenei1 encompasses the populations from the Río Santiago (Manantial 6 de enero, Manantial el Sacristán, Rio Santiago). Xenei2 is the abbreviation for fish from the Río Compostela whereas Xenei4 is reserved for the fish from the Río Ayuquila. The former Xenei3 has been renamed into Xenly1 ("Xenotoca" lyonsi), Xenei5 is now Xendo1 ("Xenotoca" doadrioi).

Habitat: 

  It inhabits springs and spring-fed pools, lakes, creeks and turbid rivers (may be severly polluted). The water is generally clear to turbid or muddy, the predominant substrates are mud, silt, sand, rubble and rocks. the currents are none to moderate. In some localities, there can be found sparse vegetation, mainly green algae, Eichhornia, Lemna, Potamogeton, Typha, Nasturtium and Ceratophyllum, in other localities, aquatic vegetation is absent. The Redtail Splitfin prefers depths less than 1m.

Colouration: 

  Fitzsimons gave in 1972 an extremly good description of the colouration: In males, the posterior half of the caudal peduncle is orange to red-orange. This bright colour continues well onto the membranes of the caudal fin or at least persists as a plae yellow-orange zone at the fin-base. The anal fin is similarly colured except for the shortened anterior six rays which remain clear. The dorsal may be dusky to dark in some populations and pale yellow-orange in others. In large males a narrow median dark stripe runs through the dorsal fin. Paired fins are pale yellow (large mature males) or clear (immatures). A bluish-black band, equal to or sligthly larger than an eye diameter, extends from the upper edge of the opercle posteriorly along the midside, becoming indistinct near the midlength of the pectoral fin. A similar dark band, beginning below the midlength of the dorsal fin and running back onto the caudal peduncle, occurs in males 40mm SL or larger. The top of the head, nape and back are olive-brown to dusky; these colours grade into lighter shades ventrally. The sides of the posterior third of the body and anterior half of the caudal peduncle range in colour from dull blue-black to iridescent turquoise. The chin, throat and belly are pale yellow to off-white. Ground colour in females, as in males, is olice-brown. Pigmentation is most dense dorsally and fades out down the sides to the venter. Scattered gold reflections are sometimes seen on the head, nape and dorsal surface of the caudal peduncle in large females. Inconspicuous wedge-shaped brown bars occur above and below the midside of the caudal peduncle and above the midside of the body from the anal origin forward to slightly anterior to the dorsal origin. The abdomen is pale white to yellow-white. Mature females have an iridescent blue-black bar behind the eye on the upper part of the opercle. A prominent black blotch on the lower abdomen begins at the anal fin and extends forward about halfway to the base of the pelvic fin. Paired and median fins are usually clear to pale yellow but in at least one population red-orange pigments are present on basal membranes of the caudal fin of mature females.

Biology: 

  Young are produced at least in March and April and probably over a long reproductive period. In aquatic stocks, broods have appeared in all months of the year, maintained  at 24 - 27°C.

Diet: 

  Adults have got strongly bifid teeth in the outer row and conic teeth in the inner row. Following Fitzsimons (1972), this species is omnivorous, although plant material forms the greater volume of food. The gut is as long or sligthly longer than TL. Besides plant material, they feed also from worms, crustaceans, spiders and aquatic insects.

Remarks: 

  "Xenotoca" eiseni is one of the best studied Goodeids. Mendoza (1965) described the trophotaenia and the ovary in detail, Fitzsimons (1972) investigated the courtship behaviour.

 

  Some aquarists report a cannibalizing behaviour, others again report that this species attacks other fish, eats their fins and bites them to death. Normally, kept on its own, this species isn't more aggressive than most of the other Goodeids and this aggressive behaviour isn't reported by all keepers.

 

  The Redtail Splitfin, its closest relatives and the Black Splitfin do not belong to the genus Xenotoca. S. Webb (1998) proposed a new generic name in his thesis for these five species that has not appeared in published form (Xenotichthys). Following the US-American jurisdiction - in contrary to other systems of justice - a thesis doesn't count as published. Therefore R. R. Miller segregated the generic name by quotation marks, a system, we follow.

 

  A rare form with speckles in females was distributed in the hobby, unfortunately, the locality of this form is unknown. H. Hieronimus (1995) suggested, that this variety may represent the types described by Rutter, others (E. Schraml, peronal communication) are of the opinion, the fish were originally from the Río Tamazula, that are now "Xenotoca" lyonsi. Both sexes were slender than the high bodied aquarium strain and are lost for some decades now.

 

  Meristic data from certain populations of this species overlaps with Xenotoca variata, and this might be the reason, why several authors (Regan 1906-08, Hubbs 1926 and Hubbs & Turner 1939, Romero 1967) synonymized eiseni with variata. Though Turner had seen living eiseni, he confirmed the synonymy of these species. Miller became uncertain about this (1955) and Mendoza found differences in trophotaenia and ovary (1965), but finally Fitzsimons (1972), who saw the striking colours of living "Xenotoca" eiseni ended the confusion.    

 

  In contrary to its wide distribution in the hobby, the forms of the eiseni-complexe (doadrioi, eiseni, lyonsi) are rare in nature and higly endangered. Only few populations from the Río Santiago basin in Nayarit are still persisting, the type location near Tepic is now dry. The populations from the Río Ayuquila and Río Ameca may be extinct already.

Husbandry: 

  Looking on the habitats of "Xenotoca" eiseni, they suggest the species is not in need of a special habitat structure as many of the locations show no or little vegetation. Nevertheless, it may prefer dense vegetation and roots (in the aquarium even dense artificial staff) to hide. In the wild, there was little to strong current to observe in the biotops, but the fish prefer areas with low current, so it won't be necessary in the aquarium to provide strong current. In the aquarium, the fish rarely hide in the shelter, but courting and impressing males as well as fighting fish of both sexes can often be seen in the open water. Fry is eaten in some cases, in others not, so it may depend on the quantity and quality of food and on the number of space to hide. When several different stages of juveniles occur, fry is often neglected, so it makes sense to add separate brought up fry to the group with a size of 1.5 or 2cm to provide these stages and get a flock breeding colony.

  The recommended tank size is at least 120 liters, bigger ones are better for sure. Dense vegetation combined with many roots and wood and free space areas for the males to impose and fight make sense. The current should be low.

  In the wild, the species seem to feed as a typical omnivore from small invertebrates, aufwuchs, algae, organic matter and insects from the surface. "Xenotoca" doadrioi can be fed in the aquarium with food of different sources, composed of different small frozen or freeze dried invertebrates (Daphnia, Bloodworms, Artemia), small livefood (e.g. Nauplia, Cyclops, Daphnia) and good flake food or tablets respectively granulat food. Fish of the "Xenotoca" eiseni - complexe feed from more vegetarian sources than representatives of the "Xenotoca" melanosoma - complexe.

  In many cases, "Xenotoca" eiseni could be observed attacking tales of other fish, so this species does better in its own tank.

  Concerning water quality, this species is in need of greater water changes (60 - 80% every week), so an automatic water changing system can be helpful. Otherwise, in combination with constant temperatures higher than 24°C, fish may get sick, lose resistance against diseases and burn themselves out. So, mainly for keeping the strain healthy and strong, give the fish a rest during winter time with temperatures lower than 20°C for 2 or 3 months so they stop producing fry. In spring, when the temperature slowly increases, they will start spawning at 20 or 21°C and won't stop until it gets colder again or gets too warm (25°C?).

  This species does very well when is kept in the open from spring to fall, starting when the temperature exceeds 17°C water temperature and cold periods are no longer expected. During the warm summer, reproduction will stop and may occur again in fall. Bring the fish in before the temperature goes below 15°C water temperature and keep them cool for the first days, then slowly raise the temperature but try to stay below 20°C over the winter time.

Locations