Cyprinodontiformes vivíparos e ovovivíparos

Livebearer Cyprinodontiformes

Espécies > Ficha da espécie > Xenotoca eiseni

Species > Species profile > Xenotoca eiseni

















Xenotoca eiseni  Hubbs & Turner, 1937

Characodon eiseni
  Rutter, 1896 ( válido como / valid as )

Xenotoca eiseni  Espinosa Pérez et al. , 1993

Xenotoca-de-Cauda-Vermelha [ Português ]

Mexalpique cola roja [ Español ]

Redtail splitfin [ English ]

Geographical distribution :

Mexico ( Hidrographic basins of Lerma-Santiago, Ameca-Magdalena and Armeria-Coahuayana Rivers ). Typic locality Rio Grande de Santiago, Tepic.

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I - Morphology Synopsis ( some meristic characters )

Total absolute lenght

Adult male : 50.7 a 77.8 mm

Adult female : 60.2 a 96.9 mm

Dorsal fin rays : / 11 ( 15

Caudal fin rays : / 18 ( 22 )

Scales on lateral line : 29 ( 33 )

Head lenght body lenght ratio ( male ) : 0,27

Head lenght body lenght ratio ( female ) : 0,26

You can find more pictures about these species availabe at the photo gallery.

II - Habitat and Geographical distribution

From all the possible ecosystems where this species can be found, ( Lerma-Santiago, Ameca-Magdalena and Armeria-Coahuayana systems  ), we will dedicate some attention only to the type locality hydrographical basins for now.

Lerma River born at about 24 kilometres from a small city called Toluca, at the central Mexican plateau. It runs over about 560 kilometres to end at Chapala Lake close to La Barca.

With 1080 square kilometres of surface this lake is the largest in Mexico, the third in Latin America and the 68º world largest. Maximum height rages from 78 and 82 kilometres and width goes up to 19 kilometres.

Water maximum level can reach about 8125 millions of cubical metres, while medium level is around 4500 millions of cubical meters. In 2002 the lake level drops as low has ever, reaching critical values around 1120 millions of cubical metres.

Maximum profundity on this lake goes as far as 7 metres while medium depth is around 4.5 metres.

It is situated at 1524 metres above the sea level and from it runs the Grande Santiago River, close to Ocotlán, that’s why this waterway is considered as an extension of the Lerma.

The Santiago crosses Jalisco and Nayarit States, covering 443 kilometres before arrive at the Pacific Ocean only 16 kilometres away from San Blas.

Two different climate typologies characterize the geographical areas of this species distribution, ranging from temperate dry to hot sub-humid. Usually on these regions there is a raining season from April to October, with precipitation annual values between 33.9 mm and something like 1800 mm.

On Xenotoca eiseni habitat air annual average temperatures goes from about 16ºC ( 60.8ºF ) to 24ºC ( 75.4ºF ) or a little bit more.

If we take in consideration Lake Chapala environment, ( even if it isn’t the most representative situation and is far to be a type locality ), we are in the presence of a semi-arid region.

Air annual average is 19.9ºC ( 67.82ºF ), almost without precipitation during the quite mild winter and spring seasons.

Maximum air temperatures sort just about 27ºC ( 80.6ºF ) or 30ºC ( 86.0ºF ), May and June, while minimum goes down to 9ºC ( 48.2ºF ) and 12ºC ( 53.6ºF ), December to February. Freezing can reach 4.1 days/year.

In this region annual precipitation reaches 875.2 mm mostly in June, July and August.

Extreme values on this species natural habitat are 13ºC ( 55.4ºF ) and 33ºC ( 91.4ºF ), but in some areas the occurrence of volcanic water flows can pull up these values.

Favourite environment of wild populations is quite assorted, and these fishes are found in rivers, brooks, creeks, lakes, dams as well as in swamps.

III - Physical-chemistry parameters

Ideal temperature range : 19ºC ( 66.2ºF ) - 31ºC ( 87.8ºF )

Tolerated limits : 10ºC ( 50.0ºF ) e 34ºC ( 93.2ºF )

Survival limits : 5ºC ( 41.0ºF ) e 37ºC ( 98.6ºF )

Ideal pH : 6.3 – 8.4

Ideal dH : 9º - 20º

Maximum salinity : 1,004 at 25ºC ( 77.0ºF )

Temperature annual maintenance for this species in captivity ( suggestion ) :

Thermal regime (1) 

Thermal regime (2)

14ºC ( 57.2ºF )

15ºC ( 59.0ºF )

16ºC ( 60.8ºF )

17ºC ( 62.6ºF )

18ºC ( 64.4ºF )

19ºC ( 66.2ºF )

19ºC ( 66.2ºF )

22ºC ( 71.6ºF )

21ºC ( 69.8ºF )

23ºC ( 73.6ºF )

23ºC ( 73.6ºF )

24ºC ( 75.2ºF )

25ºC ( 77.0ºF )

26ºC ( 78.8ºC )

25ºC ( 77.0ºF )

27ºC ( 80.6ºF )

24ºC ( 75.2ºF )

25ºC ( 77.0ºF )

21ºC ( 69.8ºF )

23ºC ( 73.6ºF )

19ºC ( 66.2ºF )

20ºC ( 68.0ºF )

16ºC ( 60.8ºF )

18ºC  ( 64.4ºF )

Each one of this table lines report a different month period.

The temperature values are provided only as a reference for captivity maintenance.

Performing on this way your action can be considered reasonable, according with the species known thermal exigencies.

It is sometimes difficult, if not even impossible, to recreate in aquarium the natural conditions, most favourable for the fish biology. The most ideal situation was, if you could be able to provide your fish a daily as well as a weekly temperature variation, like in the wild.

For better understanding about perfect environment or to simulate water temperature annual evolution according to natural habitat for this species, please be so kind and have a look to Guadalajara graphic at Wild water's temperatures ( all year round ) issue.

IV - Biology and ecology synopsis

In frequent sources, namely on some remarkable aquarium books, Xenotoca eiseni is described as a tail nibbler fish.

By such conduct this species can be considered by many hobbyists as an “ aggressive “ one, not suitable for all kinds of tank community.

While some breeder’s do agree with this detail, the majority of those who can get some familiarity with this species however don’t corroborate entirely herewith.

Maybe a reasonable explanation can be the kind of species that share with the Redtail Splitfin the same tank, or even the mishandling of a proper nutritional need.

Although opinions can not merge concerning some fierce behaviour, if this is a new species for you, don’t place the new arrivals directly on a community tank, ( specifically in the presence of smaller tank mates or long fin slow species ), as a preventative measure. Later on, after you become more familiar with your new fish conduct, an eventual decision to group them with other tank fellows can be supported by a conscious approach.

Besides different judgment concerning tail nibbling, everybody agrees about cannibalistic tendencies. Even if cannibal actions are not so often and particularly manifest with near born, the little fry with two days or more are generally left single-handedly, free from strife by the adults.

It is rather possible than some populations can produce regularly individuals with more predispositions for gnawing as well as to cannibalistic behaviour than others from different origin.

Out of any discussion, remains the fact that the suitable environment is no doubt to keep Xenotoca eiseni under more females than males group, inside a species-specific tank of no less than 100 litres of water capacity.

In the wild, we can found today lots of locations inside the natural geographical distribution with remarkable water pollution levels. Despite the fact that they can survive and keep relative prosperity in places where many of the local species are long gone, please take your best care on environmental quality.

Frequent water changes also reveal to benefit general condition, but be aware of chlorine intensity in domestic waters as well as significant temperatures disparity.

Life prey shouldn’t be disregard from captivity diet, but also important are vegetal components along with artificial flake food. Slight boiled spinach, peas or other vegetal supplement as well as industrial flake food to vegetarian species must not be forgotten in a good quality diet.

In captivity born Redtail Splitfin however, we don’t spot any reluctance to flake food at all. All the nourishing ideas in the general feeding suggestions at aquaristics section are very well accepted, including several vegetal alternatives, milled raw sea fish and molluscs and other usual live or frozen options.

The brood number is around 10 to 60 by birth, decreasing for only 4 to 5 for very young mothers during first delivery.

Newborns from this species are quite large getting around 12 mm at birth. By this reason raising them is no difficult at all.

Small particles from adult feeding as well as brine shrimp nauplii or other live prey are convenient dimensions, besides any of the usual industrial substitutes.

If free from stress causes as well as in ideal conditions, regular gestation ranges from 6 to 8 weeks, depending on water temperatures 22ºC ( 71.6ºF ) to 24ºC ( 75.2ºF ), on a winter period at least around 17ºC ( 62.6ºF ), on water quality, diet and feeding, as well as other unpredicted reasons like atmospheric pressure. Under nasty or unfavourable conditions gestation can be deferred several months.

V - Complementary notes

Based in aquarium observations, it seems that mating predilection have a propensity to occur between identical sized individuals.

Back in the wild, this behaviour can be suitable. It’s not difficult to glance that larger males can win fairly on smaller ones regarding the competition for bigger and fecund females.

In captivity, however, this conduct must call our best attention. In a short term, this natural mating performance in small captive groups, can in fact contribute to consanguinity births. Such close genetic parental relations are in fact a secure and fast step towards endogamy.

On these confine communities, young females tender to be fertilized mostly by their own brothers instead of by older males, which are more committed to spend energy fighting as best as they can for the larger females inside the group. At this instant we can be facing another possible dilemma, as those bigger males are indeed soughing after generously proportioned females, which can reveal to be in effect also their own sisters and even their own mothers too.

Unlike Poecilids, Xenotoca eiseni well-built males can reach as large as 85% or even 100% of their sought after adult female’s total length, so don’t expect many mating attempts from these individuals toward less significant females, unless they couldn’t succeed in competition for the full-size ones.

Another remarkable circumstance is that only females with mature sexual cells turn out to be easily attained for mating. Neither the species males nor we can distinguish when the right moment happen to turn up. Courtship starts above 20ºC ( 68.0ºF ) or 21ºC ( 69.8ºF ). At some point in and over such limit, males start to run after any female present, ready or not for it.

The unmistakable distinction just becomes obvious when a receptive female do not act indifferent to courtship but, instead, place herself accessible for copula.

At this point let’s also say a few words about keeping more than one Xenotoca species simultaneously in the same tank.

While Xenotoca eiseni and Xenotoca melanostoma do share out a few common wild locations in their geographical distribution, particularly and above all in some areas of Rio Grande de Santiago and Tamazula River basins, there is no scientific proof with reference to natural hybrids between them.

Back in captivity, several successful cases have been reported and hybrids are come in to existence from time to time in the hobby market. According to reliable sources, these events are so easy to take place that you only need to keep one isolated individual amongst members of the other species and such undesirable situation have effect more or less immediately.

In this particular case, the offspring resulting from such objectionable hybridization are in fact fertile, which jeopardize the survival and purity of both original parental species.

With Xenotoca variata it seams to be not the case, has we couldn’t find any positive reports at all. Almost certainly due a lesser amount of genetic closeness between this and the two preceding species, it can in fact work as a natural biological obstruction to successful crossbreed.

Now also a special reference to an atypical conduct of Redtail Splitfin in the occurrence of a capture attempt.

By what we can testify in aquarium, the astonishing inquisitiveness natural behaviour of this species is fatal for them on the first capture attempts. Home born fish, maybe overreacting to curiosity and excitement with the unfamiliar, allow us to net them easily in the beginning.

In contrast, experienced fish reveal an out of the ordinary intelligence to escape by the most unthinkable spaces in face of a netting attempt. As soon as they understand how they can overcome this challenge some even face confront serenely, instead of running in a hysterical manner around the tank, than, in the right moment they manage to escape.

VI - Threats, protection and present status

Water resources use by human societies can be regarded in terms of quality, quantity as well as of hydrologic income.

In many countries the present situation is far from be sustainable due to a tradition of unawareness about water resources management most important issues.

Where a good and effective administration of this good doesn’t exist or it reveals to be poor, pressure caused by intense human demands on domestic, industrial and agricultural water use leads to a dramatic situation.

A very considerable area of the primitive Xenotoca eiseni environment exposes at present a high rate of over-exploration as well as deterioration or contamination.

Residual waters from industry, disforestation, illegal pumping, and climate changes ( drought ), are some of the most important factors that can explain the endangerment of aquatic life.

Some of the above mentioned lacustrine habitats are turning from oligotrophic, with high oxygen levels, to eutrophic ones.

Industry and agriculture used chemicals, fertilizers, organic matter from waste waters and other ways of contamination are aggravating a biomass explosion and waters turbidity.

In the meanwhile, introduced alien species ( even from other ecosystems and continents ), had originated competition and predation relations, some times in a so high stage that the species can’t deal with these new challenges.

One impressive prospective and signal of hope is that some wild populations are capable to flourish in quite polluted waters, so this can be a confirmation of resistance as well as adjustment ability.

Even so, there aren’t by now evidences and information concerning a Redtail Splitin endangered condition, in particular taking in consideration the Red List of Threatened Species.

For further knowledge or information about this please check Livebearer Cyprinodontiformes in the IUCN Red List of Threatened Species.

Other topics available about this species :

Sugested links :

Comisión nacional para el concocimiento y uso de la biodiversidad ( CONABIO )

Agradece-se profundamente aos nossos leitores que possuam dados e informações complementares ou que encontrem neste documento eventuais correcções, o favor de nos contactarem nesse sentido.

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A comunicação e conteúdos são transmitidos no pressuposto de que não há garantias absolutas da sua exactidão e incontestável perfeição. Os visitantes e utilizadores deste sítio são convidados a ponderarem sobre o carácter provisório de alguns dados antes de os utilizarem, pelo que se assume da responsabilidade desses utentes o tipo de uso que lhes é dado.