Cyprinodontiformes vivíparos e ovovivíparos
Artigos - Mitologia P.G.A.
Articles - P.G.A.'s Mythology
By Miguel Andrade - published at this website in October 2008 ( original article printed in August 2008 )
A few weeks ago, a friend of mine has called me to suggest a new article to publish at my website.
She was frankly exhausted to deal with the hobbyist’s common opinion regarding livebearers at meetings and even expressed at a number of web forums and mail lists.
Very often it’s whispered that these so called “ lower status “ fish are the best choice for beginners, ( following just after Goldfish - Carassius auratus ).
I have asked her immediately why she couldn’t do it by herself; after all I was talking to a biologist.
She immediately shoots back, arguing that these fish were simply a new world to explore on her aquaria practice. In fact, the first Poeciliinae species have been only recently introduced at a single species tank, back her home, ( a very unusual situation for someone rising and keeping aquarium fish at a quite some time ).
Besides this point of view, there was another remark that could be, beyond any doubt, significant and finally persuaded me... there was nobody like another hobbyist to know how to select and use the right words wile speaking for others like himself.
Well, after this last consideration, I start to realise how nice this challenge could be. It has immediately become clear on my mind that some planning should start without any delay. My next assignment was regarding how I could throw a little light on some fashionable ideas on the hobby about livebearers.
But before proceed any further; let me explain first what P.G.A. is, for a start.
These are the initials of Poeciliinae, Goodeinae and Anableptinae, three subfamilies of fish where science classify a particular kind of livebearer fish.
Off course there are a number of other species that give birth live new born ( even concerning merely freshwater species ), but these PGA’s in particular have some in common... we are talking about Cyprinodontiforms, a big order of fish with some particular characteristics. Nevertheless, this opinion article is not the best place and the proper instance to put in writing something more about such prevalent features prevalent in all of them, ( although I would enjoy to do it ).
In a few simple words, and only with reference to the objectives of this piece of writing, let me however make clear that Cyprinodontiforms are an assortment of roughly 900 species distributed by a few families ( as well as sub families ), existing naturally in tropical and temperate regions and predominantly found in fresh or brackish water.
While the vast majority of fishes in general laid eggs to reproduce themselves, this order comprises about three groups that deliver full developed alive babies.
Some scientific papers describe how molecular phylogeny can be used to estimate the evolution of most important life-history singular qualities, such as internal fertilization, modifications on male's anal fin to form a copulatory organ, livebearing and placentas that evolved independently in Cyprinodontiform fishes inside the subfamilies, Poeciliinae, Goodeinae and Anablepinae.
Even so, a number of other particularities can be straightforward understood via observation or other diverse scientific methodology.
The evolution of spermatozeugmata ( packaged sperm ), for instance, it wasn’t probably a requirement for internal fertilization. At least one species with internal fertilization has free spermatozoa.
Livebearing, when considering any form of archaic sorts of viviparity or refined types of ovoviviparity, took place in the subfamily Poeciliinae.
On the other end, advanced forms of viviparity, in which the mother provides additional nourishment to the embryos by a placenta-like structure, evolved at least several times from egg-laying ancestors in the Families Poeciliidae Goodeidae and in the Anablepidae.
Some of these species are notorious as really popular aquarium pet fish, living, in some cases, for more than 100 years as “ domesticated “ animals.
Much of this is the end result of a propensity to mutations, and due to a rare number of unusual freak individuals emerging from time to time in a shoal. In some remote areas, a number of them have developed so distinctive forms, that we can find some early stages of evolution towards a new subspecies on such isolated populations.
The outcome of this amazing changeability was the starting point for a trouble-free straightforward fancy strains emergence in captivity. This was possible through progenitors artificial selection and crossbreeding between species ( hybridising ).
Those species with a larger geographical distribution in particular, can sometimes show some colour as well as morphological diversity, and contrasting fish can be found in the wild every time. Most of this polymorphism can be discovered in males ( for comprehensible reasons related with sexual competition and selection ).
Domestic fancy strains are predominantly more colourful than wild types and many have extremely long fins. Such particularities are the enjoyment and a delight for the preponderance of fish hobbyists, but these unfortunate exemplars could not survive long back in the wild, mainly as consequence of predator’s action.
The manipulation of domestic strains is in fact a really important activity but also a quite significant business today. There are world wide specialists as well as fan clubs and associations of breeders dedicated exclusively to extravagant lineages, forced by man made selection.
Every year we can find some national and international events and exhibitions, where prominent specialists compete for awards and fame with new fancy strains.
In some examples, this can even be a regulated activity, as there are, in some instances, conventions concerning anatomic patterns and body appearance. These rules are in fact greatly respected and are allocated inside separated categories.
Wild types popularity has start to decline at the equivalent speed that new fancy domestic strains arise in the market. Soon a millionaire industry of aquarium fish has progressed thanks to a few out of the ordinary man made Poeciliids in particular.
The comprehensive economical importance of pet fish market is tremendous at the present time. Some communities and even some enterprises, like a number of airplane corporations, afford impressive incomes every year from this financial system segment.
After all the above information, if you didn’t get in to the point yet, let me put in a few strait words about whose fish we have been talk before.
Probably you cant miss it if I named some well-known famous aquarium
fishes like the Guppy - Poecilia reticulata, the Platy -
Xiphophorus maculatus, the Swordtail - Xiphophorus helerii
and off course the ( several ) Mollies - Poecilia velifera,
Poecilia sphenops, among others.
The most common of fish reproduction mechanisms is no doubt that observed on ovuliparous.
Through out this method at the right moment, the female releases eggs in the water, while the male or males near by, immediately do the same with sperm to fertilize those eggs. Water is the link to the sexual cells meet ( resulting in fecundation ) as well as the environment where meiosis take place ( the embryo development ).
A large majority of Cyprinodontiforms have adopt for this sort of reproduction.
Some species at Goodeidae family and a large number of the Poeciliidae family species simply lay the eggs and the sperm, free in the water, just at the right time and under suitable environmental conditions for reproduction take place.
At oviparous fish we can observe a little variation on the ovuliparity process. In fact these species do not simply liberate sexual cells in to the water, obtaining this way a solution to put eggs and sperm in contact prior to fertilization. Instead, the oviparous male introduce his sexual cells ( spermatozoon or sperm ), in to the female body, allowing this way an internal fertilization. After fecundation, zygotes ( eggs ) are released in to the external environment ( water ) and let free.
This process can be compared with bird’s reproduction, for instance, but fish parents don’t care about the eggs like birds. This occurs in a very small number of fish species. There is at least among Cyprinodontiformes, a tiny member of Poeciliidae family, Tomeurus gracilis, who reproduces on this way.
In both above mentioned mechanisms ( ovuliparity and oviparity ), a great number of offspring must be produced in order to allow reasonable survival of zygotes and embryos. It’s easy to understand that when the progeny is simply discarded in the water it remains at predator’s mercy. To deal with this problem some species have reduced the energy consumption of a large brood by paying different levels of parental care or protection regarding when the new generation can become independent, and some new approach from a new fertilization process to increased new born size.
Even with such new strategies on the way there was still taking place the primitive independent embryo development inside the egg.
Next step come true as a approach to ensure higher survival rates. In fact, some species have progressively delay egg release until a later release of the offspring after egg hatch.
This late tactic did possibly resulted in to distinct stages.
On a first moment, some species have reached the ovoviviparity form.
After the internal fertilization took place, females do not release immediately the zygotes, but instead, they are protected inside their own body the eggs and embryos until hatching.
The only difference from ovuliparous and oviparous is the fact that the eggs are not released, but fundamentally the embryo development is still the same on these three forms. By other words, the ovoviviparous egg has all the needs to complete meiosis, so there is no other linkage with the maternal organism besides a safe environment and protection.
In the course of this strategy success, some species have than probably jump in to a more elaborated approach… viviparity.
The female body becomes than more than a simple shelter and wider interactions were slowly improved between embryos and the mother organism.
This highly developed relation comprises metabolic exchanges; including embryo nutrition, oxygen, and even antibody swap over in order to face potential diseases attack.
One first consequence from this strategy is in fact an evident smallest number of zygotes.
One other evident effect is also a lowest nativity ( as females cannot breed in little intervals as those who lay eggs ).
On the other hand, these two last ways can assure high survival probability during first stages of development and mothers give live birth full developed young, ( very well prepared to carry on by themselves ).
In ovoviviparity as well as in viviparity we can now talk about a gestation period, or said in a different way, the time ( and course of action ) between fecundation and the release of full developed fry. In both cases this period is always a process of maternal organism development and adaptation, usually a uterus visible volume increasing, circulatory as well as endocrine and gastro-intestinal adjustments, among others.
All livebearer Cyprinodontiformes are ovoviviparous or can show some different levels of viviparity.
Some Poeciliidae family members can also show an interesting way of ovoviviparity designated as superfetation. On these particular cases, we can found embryos in different phases of development simultaneous in each gestation. As they all need the same amount of time to complete development, births can take place in consecutive days or weeks, as soon as more little ones complete conception period.
Ovoviviparous females belonging to this family can also store viable
sperm for periods up to 10 months. In the absence of males, one single
succeed copula can originate as much as 8 to 9 following deliveries.
The most frequently cultivated fancy strains, held in aquarium since the end of XIX century, fit inside a model with reference to only a few species and cannot remain forever as a prominent reference or a paradigm.
Besides a natural preponderance to resist at the most adverse environmental circumstances, a extended captivity heritage had converted these “ domesticated “ fish into more adapted ones, as regard indoors and tank environment.
This is true even if compared with the wild ancestrally.
Even so, some transport awful conditions, hygiene absence at some stages of the commercial circuit as well as some pet shop’s sale tank’s background, are together responsible for quite high mortally levels even at present.
Stronger individuals, if carry on resisting while exposed to some common diseases during the commercial pathway and, above all, if quickly installed at a proper environment after arrive from a pet shop, ( like a well set tank ), they become capable of justify the allegory associating them to some of the most robust and less demanding aquarium fish.
In result of this piece of evidence, newcomers are promptly suggested to keep livebearer fish in order to gain the practice and know how essential to a successful aquaristics ( fishkeeping ).
We can’t however carry on insisting in such inaccuracy, in particular considering simply the common fancy strains as a whole and applying the same major rules for each and every species.
Even wild individuals kept in captivity can reveal to be contradictory to the general idea of livebearer aquarium fish.
This is probably why, some of the most interesting so called “ wild strains “, will probably never become popular pet fish as the fancy ones.
A quantity of the uncultivated relatives concerning the most wanted fancy strains, are in fact more exigent ones in terms of water quality as well as other essential aspects.
Several other rare species in the hobby can reveal to be extraordinary difficult to keep after all; unless you pay some extra attention to their basic needs.
Even when considering some quite resistant fish, most of them with an extended existence in extreme environments, we can in fact discover that they show an unexpected little adaptability to our regular tap water.
A few others can tolerate very unusual natural backgrounds but will hardly resist to small adaptations out of such tremendous natural conditions. Despite of that, some of these species came from remarkable environments with extreme high values in temperature, salinity or other physical and chemical parameters.
For some of the most demanding livebearer Cyprinodontiformes it is so difficult to recreate the proper environment as to a tropical sea coral reef community.
Also water temperature can become a factor of unsuccessful experiences and failure.
Many ignore why a few wild strains will not survive long in domestic environment, in particular when all the fish basic needs were properly took in consideration.
A hypothetical failure can simply happen because the demanded annual thermal regimen was not respected.
In standard circumstances, to successfully maintain fancy strains of most popular species a temperature of 24ºC to 25ºC with an annual thermal amplitude of something around 3ºc to 5ºC can be considered suitable for many.
Fish submitted to such existence are not living at the best amplitude for their biological requirements, but they will survive for an extended period of time.
This practice can however reduce substantially the longevity of several wild strains.
In some cases, a very wide geographical dispersion can even result in slight different requirements amongst wild populations of the same species.
In fact, it is possible to find livebearer Cyprinodontiformes in such large territory of the Americas that there are a few species tailored to a quite broad range of local climates.
Almost all of the fancy strain ancestors came from tropical areas of Central America or even equatorial regions of Northern South America.
Some of the noble rarities in the hobby can have their natural habitat in absolutely different kinds of climate, ( some times even kite antagonist ones ).
This can reveal that the usual indoors temperatures can reveal to be lethal if fish are kept all year round inside our domestic environment.
In some cases the comfortable temperatures for us cannot fit the fish needs at all.
Every now and then summer heat can be really harmful for some atypical species.
Also the cosy warm inside our hoses during winter months or all year round in tropical areas, can turn out to be awfully elevated for some cold loving fish.
A number of singular livebearers need at least a cool “ winter “ seasonal period and this is really essential for physical condition and healthiness.
If not lethal at least a “ warm “ winter can interfere with immunity and reproduction.
In some other exceptional cases, a long evolution in spring highly pure waters can turn out to be a handicap in captivity, especially when facing the tank close flow, where high values of nitrites and nitrates ( due to the nitrogen cycle ), as well as pH droppings can factually exterminate the fish in no time.
To avoid unnecessary fatalities with no other noticeable reason, frequent partial water changes, ( daily in some extreme cases ) will work well. A few other extreme demanding ones need chemical substances kept away from the water, ( this is also true when regarding a number of drugs and medication used to fight diseases ).
Never forget also a small number of unusual diets, lighting requirements ( for some hormonal or other physiological efficiency ), as well as some ecological primary requests, which can represent the difference between survival or failure when trying to keep some more difficult species.
Actually, in general livebearer Cyprinodontiformes can reveal to have an
exceptional adaptability to aquarium, but please don’t trust only in the
standard fancy strains know how and your personal experience with those
to evaluate all other species. A quantity of them can reveal to be such
demanding as some of the highly rated as “ hard to keep “.
Regrettably this isn’t the most accurate reply at all.
Allow me to say... not always.
Live full developed offspring delivery at birth can in fact swindle us straightforward, in particular regarding the difficulties with new born care.
Once again remember that not all the live bearer species can become the best choice for beginners... at least just by the fact they breed easy.
Breeding the common domesticated fancy strains doesn’t pose usually any factual challenge.
In a relatively short time, the beginner’s smaller tanks will be overcrowded with fry, by means of a negligible effort to save newborn from preying acts on them.
This eventuality calls our attention for the danger of a demographic boom. In a quick relatively no time, endogamy will be “ waiting around the corner “ to damage the viability and continued existence of our stock.
Nevertheless, for the majority of hobbyists, it seems that the only challenge it is how to save new birth little fish from other species as well as, in several circumstances, even from the adults of it’s own kind, ( including the mother it self and other relatives ).
Cannibalistic behaviour was developed during the evolutionary process of a quantity of species. This is probably a way of nature to fight back the same problems we face in aquarium, especially when wild fish are congested in small habitat backgrounds as in captivity.
Sorrowfully, confinement pressure ( by lack of vital space in particular ), can push some usually non cannibal species to show such behaviour in aquarium, even when the wild counterparts rarely or never reveal this perform back in nature.
As a rule, the most widespread solution to save new born and fry can become precisely the instrument responsible for what we are struggling to avoid.
In fact, the pet shop market is full of little plastic boxes ( cages ) with barred barriers where gestation females are incarcerated in dreadful conditions. According to my personal opinion, this practice is deplorable and is no doubt an attack at the most basic animal’s wrights. The consequences are dreadful to mother ( as well as to embryos ) safety and wellbeing.
As a result of expectant female’s imprisonment inside undersized anguish places, you can anticipate important newborn mortality, deliberate abortions, as well as significant fry casualty rates, to not mention stress... a lot of it.
Mother’s frustration and anguish during gestation period can cause evident healthiness problems or anomalous conduct... like cannibalism.
Yes, I know, in captivity it’s difficult to create the proper conditions. Only the largest tanks can afford to have quite fair room conditions for sustainable fish reproduction, particularly in “ ordinary “ conditions.
Even so, motherhood small tanks, prepared for each female ( or female’s small group ), is no doubt one of the most “ compassionate “ and successful way to face the problem.
As egg layers, some wild livebearers are far from be easy to produce offspring in captivity environment, so again and again, fancy strains can’t be considered a paradigm at all.
Fish just arrived from nature can show lower fertility and fecundity rates, when compared with free populations at the original habitat.
Some peculiar species reveal to be as tough to breed in captivity as several inflexible egg layers. Same extra hard work should be engaged in order to induce these particular fish to reproduction.
Yes, without a doubt it’s true that is quite easy to get a number of quite independent and well developed “ big “ babies from the majority of the live bearer, and without many of those challenges posed by egg layers from fertilization to free swimming phase. Anyway, keep in mind that to testify the end of a gestation, in some hard to reproduce live bearing species, can be as well as frustrating as to get the first eggs from hard to reproduce ovuliparous.
Even when the mother is not delaying birth, as while incarcerated inside the above mentioned “ motherliness cages “, sometimes the gestation period can extend very further than the predictable usual time for some reason.
On those species from temperate regions, a warmer then required winter period, can also be the major cause for disturbing fecundity as well as to fry health. In result of physiologic and hormonal problems, the critical cases can result in no procreation season at all.
Even the so called continuous breeding species, ( as for the most part of the fancy strains ones ), in face of various particular conditions like weather severe conditions, food chain dramatic alterations or other less understood, breeding stops for sometime.
Well, I wouldn’t be fair if didn’t confess that livebearer in general mate or copulate rather effortless and a lot more frequently than most of the egg layers spawn.
Nonetheless, even if not so demanding to mate as ovuliparous, some illustrious unfamiliar or less acknowledged species in the hobby can be really hard to have babies in aquarium.
Trouble-free to get newborn as well as fry size are the most popular arguments do impose these species to novice hobbyists, claiming their are easy breeding.
That’s a fact, live bearer newborn are quite larger and totally independent ones.
This is especially true in viviparous species. Relatively small fish ( no more than 10 cm of adult full size ), can have babies between 19 mm and 24 mm.
If naturally outsized, these independent new born can present less problems than defenceless nearly hatch minuscule fish larvae, completing the development process during a few days before become free swimmers.
remember that there are now and then a few surprises. Some large
livebearer fry are so demanding with nourishment or environments that
hardly survive in aquarium more than a few weeks without a challenging
Well; cultivated strains do have some charming colourful lineages but wild ancestors and most other species in general, can’t be awfully extravagant and quite ornate, in order to survive in nature.
Ordinary and sexual selection are in permanent confrontation during the last millenniums of each species evolution. The final result of a remarkable conditioned progression is such that actual fish end result is the consequence from thousands of generations’ succession, so they are the last end product of the prevailing propensity among these two in each habitat.
On one side of this evolutionary “ conflict “ there are the females which, ( like human aquarium keepers ), demand and show their preference for males with longer fins and dazzling colouration.
On the opposite side of the question lies the need to become inconspicuous to predators, on which nice and attractive body colouration, so eye-catching for females, is definitively not the best camouflage at all on the surrounding environment.
Equally true is the fact that long fins can delay a full speed sudden escapee sprint.
Due to this dilemma, natural populations usually demonstrate a great diversity.
Some isolated groups did anticipate the patient human work of artificial selection and do have shaped a very small number of extraordinary glamorous males, although the vast majority of individuals are not so astonishing.
Even so, the vast preponderance of species are quite unremarkable and ordinary in terms of human aesthetic valuation.
Nevertheless, keep in mid that fashion is a very susceptible passion that changes very rapidly.
At one moment red is the chic colour, but almost immediately military camouflage emerges as the up-to-the-minute stylish everywhere... but both will last during a similarly brief period of time.
For natural and expectable reasons, to guarantee a continued existence in the wild habitat, small fish that are “dressed” with camouflage are obviously not straight away observable, while a hypothetic luminous orange spot is no doubt an unmistakable blotch in the middle of the brownish and greenish surroundings.
On this debate it was expectable that people could open their minds and show a little bit more respect for nature’s architecture.
In fact, there is nothing more perfect and respectful than the final result from countless millenniums of evolution at the chain of a species continued existence.
Such “ piece of art “ may not inflame a fascination similar to our paradigm of beauty, comparable to the extraordinary sea tropical coral multi-coloured fish, but we can undoubtedly detect an interesting as unexpected beauty at animals who, nine times out of ten, people say they have no colour at all.
False eye spots, dots, lines, blots, blotches as well as all imaginable but not immediately noticeable adornment marks and false shade tones or unforeseen light reflexes, can reveal quite a face up to to boredom.
Various other more attractive colouring fish may not be comparable with these smooth designs.
Adult healthy and vigorous fish, enjoying their environmental conditions, in particular when observed under the proper lighting conditions and correct background, will swiftly glow like a Cinderella.
Some species considered too irrelevant or trivial for most hobbyists, in particular if observed inside a pet shop tank under stress conditions, can ignite such an enthusiasm later back home, not so long after being introduced at a domestic aquarium... as soon as we keep them under best or, at least, favourable environmental conditions.
Unfortunately for many of us, some of the singular atypical exceptions that can compete in a certain way, with other really charming fish, like Killies for instance, are not quite easy to find available.
In addition to any significant aspect related with bodily complexion or morphology, one of the meanings for raising Cyprinodontiformes, doesn’t lie on complex social behaviour but on their biology and ecology.
In the course of livebearer species biology, young children can softly fly from the proverbial stork that brings babies from Paris myth, to a natural world version about conception and born.
To cultivate these fish may not be an exciting display every day but, no doubt, it can reward and induce you with other unpredictable compensations.
the most unattainable enjoyments is when we can create conditions to
sustain a viable population of an extinct species in nature. This is
unquestionably a fantastic challenge.
Is it difficult to keep wild ( original ) forms when you are a novice in fishkeeping ?
Well, it depends about which species we are talking about. There are so many options, than even among those which happen to be available at pet shops, from time to time, is possible to find hard fish to try with no problem.
Keep in mind that, in general, the so called “ wild “ forms aren’t so colourful as fancy domesticated ones. A number of of these “ wild “ forms will need more care and attention, in particular if we are talking about some hypothetical rare ones.
On these three groups you can find more species associated to the idea of a sustainable aquarium practice, than in other relatively common families of ornamental fish.
Some tiny precious will even allow a regular hobbyist to find enough room to preserve a whole valuable small population, biologically viable for decades.
Preserving an original lineage, with identified wild provenience, it is one of the most modern sustainable ways to safeguard a piece of nature and to participate in this hobby as well.
When someone is successful in look after an endangered species, threatened in the original habitat by human action, is certainly a valuable civic act and a kind of remission approach as well.
Hopping that my readers will never interpret between the lines my
enthusiasm with wild forms as a direct censure or attack to artificial
selection of breeders or fancy domestic strains; to learn how to enjoy
uncultivated animals ( reminding you of to those we can find in their
natural habitat ), is unmistakably a relevant deontological progress
that will let you proud for such love paid to the true natural world
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