Something about bear biology
 

  Unfortunately, domestic strains are becoming more and more distant from the original fish. It is becoming increasingly common to find traces of other species of the genus in the relevant genetic material of these fish as a result of crosses that occurred somewhere in the recent past in captivity, namely Xiphophorus variatus and Xiphophorus maculatus.

Due to the environmental and predatory pressures to which wild bears are exposed, it is very difficult to catch males with the dimensions of cultivated forms. 

Due to the relatively wide geographical distribution, interesting differences were found in biological and morphological terms between different populations.

In this context, sexual selection plays a predominant role.

Males who have a longer sword and a more attractive color prefer females (Jerald B. Johnson & Alexandra L. Basolo, 2003).

The fact that a female allows herself to be invited by a male who stands out too much in the environment that surrounds her can even endanger her life, as they become easily targeted by predators (Jerald B. Johnson & Alexandra L. Basolo, 2003).

As with other live-bearing species, two different species of males sometimes appear in the same flock.

In the case of the bear, this condition was described in terms of the population of the Jalapa River.

The first of the two species is characterized by males having a characteristic dark line along the body ("males of the black line"), while the others have a red or brownish side line ("males of the red line").

Even if they reach sexual maturity in front of males with a red line, males of the black line will never become dominant in the group. However, males with a black line are always smaller than competitors (almost half the size), who continue to grow until they reach sexual maturity, reaching it only after a few weeks or a few months.

The infamous affection of females for the red line and their dominance over the black line did not lead to the extinction of the former. Males from the red line carry genes that allow them to maintain a competitive breed, and in addition, males from the black line can mate earlier, albeit with a lower success rate in mating.

Another important difference, in addition to pronounced behavioral facts, is that offspring derived from the black line are mostly males, while those from the red line are females (Dierk Franck, Agnes Müller, and Natascha Rogmann, 2003).

The bear is characterized by violent behavior, especially among males who compete for females and cause violence.

Conflicts can also be observed in the aquarium, although the extent of these challenges and their outcomes depend not only on the genetic heritage of the fish, but also on the dimensions of the aquarium, the composition of the group and the concentration of individuals.

Male size is not a condition for success in these disputes. The physiological aspect and motivation can lead to the subordination of a larger male to a smaller one.

There is always a complex network of relationships between groups of this kind as a hierarchy is formed, a behavior that is also noticeable in the aquarium. Therefore, it should be borne in mind that the habitat for healthy maintenance of the group must always reflect 3 very important factors, namely that adult animals can reach 15 cm, that dominant animals hunt others, (that it can cause fatal injuries if persecuted refuge) and, finally, that this species has a relatively complex social behavior.

Such behavior is discussed in depth in the article “Social organization of small heterosexual groups of green bears (Xiphophorus helleri) in captivity” (Jacques P. Beaugrand, Jean Caron & Louise Comeau, 1984).

As with most other species of the genus Xiphophorus, countless testimonies of sexual reversal have emerged over time (the individual functionally belongs to one sex and genetically the opposite, or "changes sex" at a given time).

Although not very common, this phenomenon occurs even in populations raised in captivity and whose origin is unknown. 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 in one aquarium for one to become male or vice versa.

Interestingly, females who have already had offspring can become males, fertilizing other females who again have offspring.

The experience of complete sexual reversal was very well documented in the article “COMPLETE SEX-REVERSAL IN THE VIVIPARO TELEOST XIPHOPHORUS HELLERI” (JM Essemberg, 1926).

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

Green bears eat dry food (flakes), fresh or frozen food and give excellent results when they receive live food. In addition to lyophilized flake food, artemia, mosquito larvae, tubifex, daphnia, all live or frozen are highly recommended. As a supplement, they accept minced meat from molluscs or most sea fish. 

There is a noticeable difference in growth and fertility between fish that often feed on natural foods and those that have access only to artificial alternatives (DP Kruger, PJ Britz & J. Sales, 2001).

The bear has continuous reproduction as long as it is within ideal limits of temperature and photoperiod (exposure time).

In captivity, cannibalism in newborns is common and highly effective, with 85.2% of these victims trapped by the female at the bottom and 14.8% at the surface, according to a laboratory study (CLW Jones et al, 1998). In this same investigation, it is proposed that sufficient surface shelter be provided to preserve as many offspring as possible. But it is an extremely fertile species.

The period between two litters is usually between 24 and 30 days, with 28-day cycles being very common. This duration is closely related to temperature and food.

The duration of labor itself can range from 2 pa to more than 10 hours (CLW Jones et al, 1998).

The interval between first births can be irregular and can occur between 27 and 90 days.

Fertilization occurs about a week after birth.

Successful copulation can result in 5 to 9 consecutive pregnancies, as females can retain sperm in their body for a period that can last 2 years in this species.

In tropical regions, reproduction can be continuous. The ideal temperature for pregnancy is between 22 ° C and 26 ° C, and any reproductive activity below 15 ° C and above 29 ° C is interrupted.

Females who have been exposed to distress or placed in hatcheries for live births may have a problematic pregnancy, leading to a significant proportion of the offspring being stillborn or having serious problems.

Younger females have 20 to 40 offspring, and more than 240 can be fully developed.

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