Cyprinodontiformes vivíparos e ovovivíparos
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Species > Species profile > Poecilia sphenops
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Adult male : 49.7 a 60.9 mm
Adult female : 60.5 a 9.8 mm
Caudal fin rays : / 22 ( 24 )
Scales on lateral line : 32 ( 34 )
Head lenght body lenght ratio ( male ) : 0,23
Head lenght body lenght ratio ( female ) : 0,19
II - Habitat and Geographical distribution
According to most trustable sources, Poecilia sphenops wild populations can be found from Pacific and Atlantic coast of Mexico to northern Colombia, including nearly entire Central America.
Some other sources also include some parts of Venezuela in its range, but some confusion is probably made with other species of this complex as well as some established feral populations introduced by man, in consequence of aquarium release.
Wild Mexican Mollies can take advantage of a vast number of diverse ecosystems, so a great variability can be expected from them, as result of an evolutionary adaptation to these distinct environments.
Larger concentrations occur in low altitude coastal areas, but a considerable number of local populations are also established in continental and medium altitude areas, in running or in slow motion waters.
One of the most conclusive facts that may limit the species geographical distribution is in fact temperature. Poecilia sphenops is common inside regions where water temperature range from 18ºC ( 64.4ºF ) to 28ºC ( 82.4ºF ), ( while some populations do survive in environments where extremes overcome these margins ).
Besides a massive number of estuarine and mangrove biotopes, some populations do look for the coastal oceanic waters in a seasonal basis and others that frequently penetrate regularly in the sea searching for particular conditions.
Intriguingly, a great salinity resistance is usual even on those individuals belonging to lakes and rivers from deep inland, with not contact at all with the sea.
There are also some isolated groups in unusual environments almost subterraneous, locally known as “ cenotes “ as well in some waters scarcely inhabited by other fish due to chemical extreme characteristics.
Malcom S. Gordon and Donn Eric Rosen in a work under the title “ A Caverniculous form of a Poeciliid Fish, Poecilia sphenops, from Tabasco, México “, have described, in 1962 a rare population living in tremendous conditions.
The article describes very less pigmented fishes, showing reduced ocular proportions in several levels of degeneration, and prominent lips found in a cave environment.
While they show evident regression characters and some particularities, these extraordinary creatures have developed powerful tools to survive in such unusual background.
Adult size varies with specific locations inside this cavern and the particularities described before can also become more or less evident according to the fish placement as darkness is not uniform.
This discovery took place during a field expedition in 1944, planned by Dr. M. W. Stirling from the Bureau of American Ethnology of the Simthsonian Institution with his wife. With he couple was also Mr. R. H. Stewart, representing the National Geographic Society.
The location is “ Cueva del Azufre “ ( also known as Cueva de la Sardina, Cueva de las Sardinas or Cueva de Villa Luz ), not far from the village of Tapijulapa, in Mexico.
During that same visit to this preserved habitat, this expeditionary group describes a local population of pale little fishes from the same kind of other living outside in open air.
This is considered as the first description of a caverniculous Poeciliid in the world. Preserved specimens brought from Mexico were identified by Dr. Robert R. Miller from the U.S. National Museum as a species from Mollinesia genus.
20 years later, in 1964, C. Kosswig, N. Peters and C. D. Zander collect the first live specimens. These fishes are than identified as Poecilia sphenops.
The first behaviour lab studies took place with this lineage.
Several collections of live and preserved fishes were after that gather from the caves in further occasions. The expeditions of 1970, 1975, 1982 and 1996 are described in several sources, as well as several restricted scientific observation missions between 1970 and 2000.
After quite convoluted identification mission in the start, this cave population was classified later as a Poecilia mexicana after all. Today this population is on focus evidenced in many scientific articles related with several of its notable specialization to survive in the darkness of underground waters.
Tolerated limits : 15ºC ( 59.0ºF ) e 35ºC ( 95.0ºF ) domestic strains are rather thermophilic
Survival limits : from 7ºC ( 44.6ºF ) to 14ºC ( 57.2ºF ) and from 38ºC ( 100.4ºF ) to 43ºC ( 11.2ºF ) according to population. Domestic strains are less tolerant.
Ideal pH : 7.4 - 8.5
Ideal dH : 11º - 32º
Maximum salinity : from 1,025 ( 33,7 ppt ) to 1,038 ( 42,2 ppt ) ( according to population )
Temperature annual maintenance for this species in captivity ( suggestion
This species show a wide tolerance to environmental factors and a astonish adaptability.
Before man made spreading of feral establish introductions, it was possible to find these fishes very well harmonized with fresh and brackish waters, as well as occasional sea penetrations from some populations on coastal locations.
This Molly show evident preference by lower depth and relatively small water bodies, forming shoals near shore on the largest ones, like many other members from the Poeciliinae sub-family.
Even it doesn’t reveal to be a very well prepared fish for fight against fast flowing water; this species can penetrate up river, mainly at dry season out of the big floods during intense raining showers of tropical climate.
In natural habitat, chief concentrations are composed mainly by females foraging in group, while males around fight for best chances to mate with more receptive females or simply using the sneaky copulation method.
Unlike bigger dorsal fin Molly species, in small fin ones mating rituals and male exhibition before copula are not common.
Mating is always a male initiative all the way through available or more receptive females.
Some larger sized males can often defend territories expulsing other competitors from females in the nearness, while minor ones simply take females by surprise.
Dorsal fin extent and dimension isn’t so important on female choice has in larger dorsal fins species.
All males react to hypothetical resistance to mate from females with vigorous attempts.
Sexual selection or simple opposition is always a topic of discussion in those cases where some females can avoid mating efforts by some specific males inside a community.
In the wild Mexican Molly is a continuous breeder in a great area of original geographical distribution. This year round cycle is only broken up by very specific less usual events, in general related to natural catastrophes or abnormal remarkable meteorological conditions.
Due to very wide geographical distribution some diet and available seasonal food accessibility can be detected.
In regions where daily and annual temperature amplitude is quite short, there is some variance between raining and dry seasons, but in general there is a broad abundance of sustenance, but the nourishment type can show a discrepancy in each period.
Seasonal assortment and differentiation in abundance as well as in dietary take place in wider range temperature regions.
Commonly this Mollies feed on aquatic insect ( in particular Coleoptera, Diptera, Hemiptera, Odonata, Plecoptera and Trichoptera ), fragments, leaves, fruits or seeds from marginal terrestrial plants from the Tropical rain forest, algae and micro-algae, a few ( rare ) aquatic plants, as well as a number of non aquatic insects ( Coleoptera, Diptera, Hymenoptera and eventually Arachnida ).
All this diet components aren’t available uniformly in any time of the year. Aquatic insects are found in larger percentage in fish digestive system from November to April ( dry season ), while between May to October ( wet season ) vegetal matter is usually a most significant diet component, which includes terrestrial plants mater, fruits and seeds, as well as non aquatic insects.
Such wide distribution and population’s variability could demonstrate an equally complex and diverse diet throughout the extensive geographical distribution, however the strong preponderance on vegetarian first choice is still universal.
In captivity, domestic strains while confirm such tendencies, do adapt perfectly to protein source food. Even if more “ carnivorous “ foodstuff are not rejected, vegetarian components must not be forgotten in the name of animal’s good health. 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.
Nonetheless, you should also alternate very often vegetal matter and flakes food with live ( or frozen ) prey, usually brine shrimps and insect small larvae. As ever the nutritional natural needs can be reproduced in aquarium as healthy and strong the fishes will thrive.
This is one of those species where flake industrial food is not a problem. With such low demand for exclusively quality diet, sometimes aquarium bred Mexican Mollies do suffer the deleterious effects from inconsequent diet. All the nourishing ideas in the general feeding suggestions at aquaristics section are very well accepted, including several vegetal alternatives, brine shrimps, mosquito larvae, small aquatic invertebrates and other usual live or frozen options. Domestic populations, also accept milled raw fish and molluscs and spirulina flake food as well as domestic cattle and hunt minced raw meat from time to time.
Even under inadequate diet and food shortage rarely new born and fry are molested by adults.
The brood number is around 10 to 80 by birth, decreasing for only 7 or 8 for very young mothers during first delivery to around 120 for full-size larger females in optimal conditions.
Poecilia sphenops newborns are quite well proportioned and obviously larger than almost all the ovuliparous species. By this reason raising them is no difficult at all.
Even if proper algae for first ration are not present inside the tank, small particles from adult feeding as well as brine shrimp nauplii or other live prey of convenient dimensions, besides any of the usual industrial substitutes.
If free from stress causes, regular gestation ranges from 28 to 45 days long, depending on water temperatures and quality, diet and feeding, as well as other unpredicted reasons. Under nasty or unfavourable conditions gestation can be deferred several months.
Very small tanks, delivery cages and aggressive species in the same community are evident suspicions to explain long gestation periods when everything seams to be perfect. Also inadequate temperatures and inadequate diet can justify long delays.
Brackish water setups and marine salt addition in fresh water aquariums is optional because salinity needs will depend on original wild population. Once usually is impossible to find domestic strains primitive natural provenience ( and many of Mexican Molly strains in the commerce are in fact hybrids ), for advisable salinity levels each animal behaviour and performance should be take in consideration.
In any circumstance water salinity must fluctuate frequently, as it will work mostly to reduce some strains hypothetical osmotic stress or when a group is often under fungus harassment in plain fresh water.
The complex member’s geographical distribution ranges from Mexico to Venezuela, and that’s probably why sometimes Poecilia sphenops natural extent can be confused with the entire species group in some of our sources.
The morphology of this species can be sometimes only superficially correlated, but in the past some populations were classified as separate species justified only on colouration or minimal distinction, which led to a big chaos on the Mexican Molly taxonomy.
Classification irresolution is not ended but the major doubts didn’t last until the end of the XX century. This matter is still a good topic for some evolutionary biology scientific debates as well as a very regular subject of many new works.
Two different views of this issue were in opposition until a few years ago.
In one of the sides, scientists had classified this species as polytypical, with a natural range from Rio Grande to Venezuela, including a few islands in the Caribbean Sea and in the Golf of Mexico.
On the opposite, another important theory was the species complex status, concerning about nine independent ones, with quite the same geographical distribution.
Later on, new scientific evidences ( now also based in DNA as well in behaviour and not only in morphologic characters ), have decide the new tendencies about the complex classification.
Based on the more recent paper works, it is very accepted today an entirely new revision on the Poecilia sphenops complex based on genetic models that allow a better understanding on these species evolution and closeness.
Some much differentiated populations like the Rio Balsas Mexican sphenops population, are not considered as an autonomous species, but instead considered a very divergent one.
There are several versions about this species complex composition but they are not very far from this :
This way we can look upon two different “ branches “ according to the next geographical division :
Poecilia mexicana limantouri
While observing some wild Mexican Molly populations images we can easily conclude that there is in fact a quite evident differentiation concerning some of them.
Speciation roll, whereas an important issue of biodiversity is not yet very well studied with this species.
Natural hybrids with some related species can also promote some difficulty on classification.
Breeding strategy and behaviour are becoming more and more also important tolls to differentiate species, but that implies field observation for long periods.
A final note on domestic strains usually found in the business.
Unfortunately “ pure “ Mexican Molly specimens are eventually rare nowadays. An expressive majority of the fishes sold as Poecilia sphenops are hybrids or can even belong to one of the related species.
Precisely trough crossbreeding it was possible to reach some of the domestic strains, however it’s acceptable than short fin all black ones, can still belong to this species.
The full black strain was full developed around 1920’s in the United States of America.
Chean Yam Meng has selected the strain called Lyre Molly in Singapore in the 1960’s.
All other short dorsal fin can be very close to original wild ancestors, but other forms are in fact Poecilia mexicana or even a hybrid between these species.
Even the classic Liberty Molly, ( countless times used for wild strains of Poecilia sphenops ) can actually in many cases be a Poecilia mexicana domestic strain.
Also many of the available images with reference to Mexican Molly ( Poecilia sphenops ) in Internet are other known species or hybrids and some confusion is also made with Atlantic Molly ( Poecilia mexicana ) due to scientific as well as common names misunderstanding.
As natural distribution is in fact tremendous, in the near future a situation of intense threatening upon this species isn’t predictable. Nevertheless, in some restricted areas there are right now situations where there are already populations under harass, suffering from a number of different risk extent.
For further knowledge or information about this please check Livebearer Cyprinodontiformes in the IUCN Red List of Threatened Species.
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