Biology  
 

  In a study published in 1977 by Klaus D. Kallman and Valerie Borkoski, entitled “A sex-linked gene that controls the onset of sexual maturity in female and male platypus (  Xiphophorus maculatus), fertility in females and adult size in males ”, we are aware of some very important differences in sexual maturity and fertility.

Platforms of both sexes are known to reach sexual maturity between 5 and 73 weeks of age, depending on their genetic heritage (Kalman and Borkoski, 1977). 

As with other known species of the subfamily Poeciliinae, animals of both sexes have the same growth rate, but males slow down or virtually stop development from sexual maturity onwards, those that reach this level remain lower than those later.

Under the same maintenance conditions in the aforementioned study, males from different study populations reached sexual maturity on average with different ages and sizes. In one of the studied populations, this phase occurred at 21 mm, corresponding to 8 weeks, the other observed populations reached the same developmental stage between 25 and 29 mm, i.e. about 11 to 13.5 weeks. On the other hand, males from one of the populations stopped growing only at 37 mm, which is approximately at  26.5 weeks of age (Kalman and Borkoski, 1977).

Another important difference between populations that can be observed mainly between those coming from Mexico and those from Belize is the fact that there are two different types of gender determination mechanisms in the species.

Three sex-linked chromosomes (W, X, and Y) have been identified in the natural population, so the sexual genotype of females may be WY or WX, and in males XY or YY, (Kallman 1973).

By genotype is meant the genetic content (or specific genome) of an individual in the form of DNA.

In Platius from the northern part of the range (Mexico) the male is heterogamous (XX - female, XY - males), in the southern part (Belize) and among most native genera the female is heterogamous (WY - female, YY male), (Mac Intyre, 1961).

As with other species of the genus Xiphophorus, countless pieces of evidence of sexual reversion have emerged over time (the individual functionally belongs to one sex and genetically the opposite).

Although not very common, this phenomenon occurs mainly in captive-bred populations of unknown origin. These strains usually include in their genetic material traces of crossbreeding between different varieties and populations, so their value as a subject of scientific research is questionable.

Contrary to popular belief, it is not enough to have only females left in one aquarium for one to become male or vice versa.

In nature, these fish are omnivorous and feed on almost all living organisms of suitable dimensions, namely zoobenthos and zooplankton, aquatic invertebrates, insects, but with a wide variety of plant substances (especially plant debris and algae).

In addition to lyophilized flake food, shrimp, mosquito larvae, tubifex, daphnia, all live or frozen are highly recommended.

In captivity, cannibalism is rare and appears to be a very effective signal for food and environmental shortages.

Of course, in limited environments such as small aquariums that have no shelter for the young, adult fish that are improperly fed and accustomed to seeing the young as food will certainly take every opportunity to get an accessible form of live food.

The period between litters usually ranges between 26 and 29 days, with a 28-day cycle being very common. This duration is closely related to temperature and food.

Fertilization occurs about a week after birth.

Younger females have 20 to 40 offspring, and fully developed even more than 60. 

Sterility has been observed in females of this species.

Presumably, these are internal causes, namely a phenomenon equivalent to ovarian degeneration or another organic cause, so that animals affected by this health problem stop reproducing.

This species poses no problem at the behavioral level and can be included in any mixed aquarium as long as aggressive species or predators do not endanger its safety.

Disputes between males are completely harmless to the remaining inhabitants of the same aquarium and​​ they rarely cause physical consequences.

In the early 1920s, it was found that some species of the genus Xiphophorus could be crossed very easily.  Their hybrids are characterized by the fact that they are often fertile and give offspring.

This phenomenon is so common that it is not good to have different species of this genus in the same aquarium.

The result of crosses, shows the characteristics of both species, the fact is that the fish are intermediate in appearance. Thus, it is possible to determine some dominant characteristics of one or even two species in a single hybrid in generation F1, and so on.

As a result of these experiments, hybrids sometimes occur that show established originality in relation to the parent species. Certain traits inherited from only one of the original species may show special vigor in this mixed offspring.

In both the U.S. and Germany, scientists soon noticed that some crossbreeding results during Xiphophorus led to a special incidence of melanoma, one of the most deadly skin cancers.

These melanomas are due to problems in the formation of melanistic markings that occur in the pigment of some hybrids.

Apparently, this provided researchers with an excellent starting point in the fight against cancer.

Based on these phenomena, there have even been some models and systems that have become instruments of essential utility in studying the progression of melanoma.

Interestingly, the pigmented cells in these fish are prone to developing diseases that are biochemically, morphologically, and physiologically comparable to those in humans.

The methods used in platia also include radiation, which gives scientists insight into the incidence of this type of cancer and its development.

Through the next generations of animals treated in the laboratory, researchers can see the progression of melanoma through a phenomenon called genetic expectation.

These well-known aquarium fish of ours have become powerful instruments in the study of heredity in this type of disease.

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Source: http://www.viviparos.com/