Cyprinodontiformes vivíparos e ovovivíparos
Espécies > Ficha da espécie > Xiphophorus hellerii
Species > Species profile > Xiphophorus hellerii
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Adult male : 47.5 a 139.8 mm
Adult female : 56.9 a 150.6 mm
Caudal fin rays : / 8 ( 10 )
Scales on lateral line : 26 ( 28 )
Head lenght body lenght ratio ( male ) : 0,20 / 0,19
Head lenght body lenght ratio ( female ) : 0,18
From all species of it
genus, Xiphophorus hellerii is the widest extended in territory,
so populations of this fish can be found over a major geographical
distribution. This is also the species found in the largest variety of
Tolerated limits : 13ºC ( 55.4ºF ) e 35ºC ( 95.0ºF )
Survival limits : 9ºC ( 48.2ºF ) a 11ºC ( 51.8ºF ) e 39ºC ( 10.2ºF ) a 41ºC ( 105.8ºF ), depending much on original population
Ideal pH : 7 – 8.2
Ideal dH : 9º - 19º
Maximum salinity : 1,011 ( 15,4 ppt )
Sometimes it’s still possible to buy Platy strains with vestigial genes from other close species like Xiphophorus variatus and Xiphophorus maculatus. This situation is quite widespread and results from earliest hybrid ancestor’s incorporation on that breeding line, somewhere in a not remote captivity precedent.
Thanks to a quite wide geographical distribution, we can find some interesting biological as well as morphological differences between Green Swordtail populations, impossible to distinguish among cultivated fancy strains, ( besides body colour combinations in different patterns and man made selection induced long fin lines ).
To illustrate a simple plain idea about wild fish variety, there is an example at the Gallery section of this website on wild strains of Xiphophorus hellerii.
This variability is so evident that by the end of 1960’s taxonomical studies point towards several subspecies :
Xiphophorus hellerii strigatus, ( Regan ) : Mexico – Papaloapan river and Coatzacoalcos river.
Xiphophorus hellerii guentheri, (Jordan & Evermann ) : México - Laguna Sontecomapan, Grijalva river, Usumacinta river basin ( Mexico and Guatemala ); also in Guatemala and Belize – rivers running in the direction of the Atlantic Ocean, and all geographical distribution inside Honduras.
Xiphophorus hellerii signum ( Kallman & Atz ) : Guatemala – Chajmaic river.
Xiphophorus helleri alvarezi ( Rosen ) : Mexico and Guatemala – Lacantún river.
Xiphophorus helleri alvarezi, Rosen, 1960; ( valid as )
Xiphophorus alvarezi, Wischnath & Foerster, 1985
Even so, wild populations from several species under strict close contact with predators do show evidence of larger individuals, specially when compared with those others free from such stress, ( and this one is far from be an exception to this rule ).
Sexual selection had an important role on the species morphological variability.
Females fill more attracted and select males on the basis of visual cues, like melanophore patterning as well as male’s longer tail appendices, ( Jerald B. Johnson & Alexandra L. Basolo, 2003 ).
The counterpace is that a highlighted individual is also more evident to predators, resulting in conspicuousness due to more elaborate ornamentation.
The simple fact of a female’s let herself to remain in the presence of such marked male during courtship, can put in danger her life too, as they both become conspicuous to near by predators, ( Jerald B. Johnson & Alexandra L. Basolo, 2003 ).
The evolution of elaborate male traits is a balance between female selection and natural selection.
Besides caudal appendices, there are also distinctive marks found at wild animals, some of which can reveal to be somehow common in several populations.
Alice Marrin Kerrigan, at her paper “ The Inheritance of the Crescent and Win Spot Marking in Xiphophorus hellerii “, describes in detail the genetic role on the transmission of such patterns.
Has in many other Poeciliinae species it’s possible to find two distinctive types of adult males thriving in the same group.
For Xiphophorus hellerii this occurrence was also described for the Jalapa basin population.
One of these unique varieties of males is composed by those with a dark lateral line, while the rest are those from the red or brownish one.
The dark line male’s reach sexual maturity always sooner than the “ red “ type. Nonetheless, even when they are still 3 mm to 5 mm larger in size, as rule they are submitted during the disputes with the red opponents inside the group.
Anyway, dark line individuals are always shorter than reddish ones, typically half sized on full growth size.
The explication for this unequivocal size discrepancy lay on a simple biological fact. Poeciliid males grow on an observable manner only until they reach sexual maturity. As the red line achieve sexual maturity later, some times weeks or even months after their dark line counterparts, growth do not stops and they make the difference.
Female’s notorious preference for red line partners and the clear dominance from those over the dark line ones, it is far to be enough to the extinction of the weaker male’s type.
Red line fellows carry dark line genes, which allow to find later some concurrent type descendents on their own progeny. By the fact of dark liners been able to fertilize females earlier, this allows them to perpetuate the lineage, even if performing with lower successful mating rates.
Another noticeable and relevant differentiation between these two male types lays on the respective descendents sex ratio.
Dark line babies are predominantly males, while red line ones are females, ( Dierk Franck, Agnes Müller & Natascha Rogmann, 2003 ).
Mating success does not depend only on sexual selection made by females or the male type.
Males establish dominance hierarchies and keep fighting in aggressive interactions with others.
Such conflicts can even remain in aquarium as part of the ancestral heritage. The frequency and end results rely much on tank size and available space, group composition and number of individuals as well as the concentration of fish.
Dominant males tend to be larger in size, with larger swords, but the success on the disputes doesn’t depend so much in individual size as we can imagine. Physiology and self motivation can turn this relation upside down and the largest being every now and then submitted by a smaller one.
In every fitted pool of Green Swordtail there is always a complex network of social relations and a noticeable hierarchy.
This behaviour is also perceptible in aquarium, so keep always in mind at least 3 details in order to keep a hale and healthy group in captivity : adult size can reach 15 cm, dominant animals do pursuit weaker ones with possible mortal injuries if the harassed ones can find enough space to run away or to seek for refuge and the complex social interactions who need some vital space to manage.
Such group interactions are very well detailed on the paper “ Social organization of small heterosexual groups of Green Swordtails ( Xiphophorus helleri, Pisces, Poeciliidae ) under conditions of captivity “, ( Jacques P. Beaugrand, Jean Caron & Louise Comeau, 1984 ).
Along with other species inside the Xiphophorus genus, Green Swordtail is also reported in numerous sources regarding spontaneous sex reversal ( an individual who is functionally from one sex, but genotypically from the other, or even successful sex changes during an individual live period ).
This is not at all a frequent occurrence. Most of the cases take place in domesticated fancy strains of unknown ancestry which have been bred by hobbyists or dealers. Such strains usually include interracial or interspecific hybrids and are thus of questionable value in scientific studies.
It is simply a very popular myth and there is no accuracy at all on the accepted judgement that if you keep only females in a tank, sooner or later one of them will become a male as well as vice-versa for males too.
Females can in fact develop into fertile males and fertilize other females, even after having give birth several times during an anterior phase of their lives.
There is a very well documented matter about sexual reversal on Green Swordtail presented at the paper “ Complete Sex-Reversal in the Viviparous Telost Xiphophorus helleri “ ( J.M. Essemberg, 1926 ).
Natural nourishment of this species is the omnivorous kind. Beck in the wild, these fish consume almost all little live prey of convenient size, especially zoobentos and zooplankton, aquatic invertebrates, insects as well as a lot of vegetable stuff ( particularly detritus and algae ).
Captivity feeding does not offer any problems.
Xiphophorus hellerii tolerate very well dry food ( flake ), freeze-dried, frozen, fresh aquarium fish food or live prey for most spectacular results.
The use of same diet than other popular Livebearer species is proper without any special complement or concern.
Flake foods are very well accepted but, if possible, always include also brine shrimps, mosquito larvae, blood worms, tubifex, daphnia, ( alive or frozen ).
You can add also milled row, fish or molluscs from about all kinds used on human diet. Infrequently, once in a blue moon, you can use row meet from cow, pork, rabbit or birds, without any fat at all.
Keep in mind that there is always a recognizable distinction in growth rate and fecundity between fish community of this species feed on natural foodstuff and those who can only get artificial alternatives, ( D.P. Kruger, P.J. Britz & J. Sales, 2001 ).
This is a continuous breeding season kind species. While temperatures still remain under ideal values and photo-period allows it, they reproduce incessantly.
Cannibalistic conduct is natural and an instinctive behaviour. Prey on babies and fry is highly effective.
Mothers giving birth can predate around 32,5% newborn. In a lab study it was observable than 85,2% of the victims from this conduct were preyed by parturient females near the bottom and around 14,8% at surface, ( C.L.W. Jones et al, 1998 ). To save the largest number of young the same study suggests effective surface sheltering for the little ones who run for safety protection.
Anyway, we are talking about a considerably prolific species.
A Green Swordtail female can spend something from 26 to 29 days between deliveries, but, as a rule usual intervals are 28 days. This period is interrelated with temperature and feeding above all.
Delivery work can take from 2 hours up to 10 hours long, ( C.L.W. Jones et al, 1998 ).
First births can be very irregular in young females. Usually an interlude from 27 to 90 days is more expectable than a regular start.
Fertilization takes place about a week after delivery.
A successful mating can originate from 5 to 9 consecutive gestations. Females can store viable sperm for periods up to 2 years.
In tropical regions uninterrupted reproduction takes place where temperatures rage from 22ºC ( 71.6ºF ) to 26ºC ( 78.8ºF ), the ideal temperatures for gestation. Any reproductive activity will cease below 15ºC ( 59.0ºF ) and above 29ºC ( 84.2ºF ).
Females subjected to maternity cages will face permanent agony and suffering. They can refuse to give birth for long periods. On the other hand, a great amount of newborn under these conditions will face complications or even be expelled death by the mother.
A birth can result ultimately in a total between 20 and 40 newborn in younger females and something around or little more than 240 in full developed ones. With age, older females will become reproductively more instable and the gestations tender to become irregular and to look a lot like the initial cycles.
Feeding newborn and fry will be no particular problem at all. This species will fallow usual needs from other members of Poeciliinae sub-family.
Expected male disputes don’t harm other fish around, but can result in injuries to the antagonists itself, including the death of the weaker in result of direct effects or in consequence of posterior complications.
By early 1920’s it starts to become evident that crosses inside Xiphophorus genus were quite undemanding. Green Swordtails can readily produce hybrids with closely related species if they both are placed together in the same environment.
What was new by the time that hobbyists get in contact with the first hybrids was the impressive number of combinations that could originate fertile offspring as well as progeny from both sexes.
These occurrences are so usual that is even advisable to keep these species apart and never let them cohabit in the “ small “ space of a domestic tank.
Cross births include generally both parental species perceptible contributions and intermediate bodily appearance is typical.
By the above-mentioned facts, these F1 hybrids and their descendants do allow that some sort of distinctions from one, or from both parental species, can be genetically fixed with no trouble. In some special situations, a number of characteristics from one of the two progenitors arise more strongly than never at these hybrid descendants.
That is the case of melanoma, one of the most deadly health disorders, commonly known as the skin cancer. So evident was this happenstance that starts do earn particularly scientist’s attention in USA and Germany since little after of first crosses.
These fish melanoma is some how related to melanic marks very common in certain strains and among some hybrids in particular.
As we could expect, such prevalence of the disease on these extraordinary small lab partners, soon develop into a quite obvious talented work filed for scientists at cancer investigation.
Since than, some models have become popular, and these species in particular turn out to be extremely useful instruments on the study of melanoma mechanisms and progression.
An incredible coincidence is that, remarkably, fish pigmented cells vulnerable to the disease are morphologically, physiologically and in biochemical terms, quite similar to human cells.
Investigation methodology used with Xiphophorus also include radiations, providing scientists a perspective about how this kind of cancer evolutes as well as it incidence.
Right the way through subsequent genealogy of laboratory manipulated fishes; investigations can expose a great deal of melanoma progress from generation to generation by means of genetic anticipation.
Next time you pay attention to your aquarium inhabitant’s of this genus, please don’t forget their relative’s important role at cancer hereditarily studies.
In the article “ Xiphophorus Interspecies Hybrids as Genetic Models of Induced Neoplasia “, ( Ronald B. Walter & Steven Kazianis, 2001 ), we can learn about this issue and get a few clues concerning this kind of work.
Another suggestion is “ Animal model for ultraviolet radiation-induced melanoma : Platyfish-Swordtail hybrid “ ( Richard B. Setlow, Avril D. Woodhead & Eleanor Grist, 1989 ).
VI - Threats, protection and present status
The specie conservation status is not an issue for concerning at the moment and it is not in the I.U.C.N. Red List.
For further knowledge or information about this please check Livebearer Cyprinodontiformes in the IUCN Red List of Threatened Species.
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