Emeraldking-aquatics livebearers

Introduction to livebearing toothcarps

Livebearing fish species occur in a range of fish families and are to be found in multiple parts of the world. All have their own requirements and behaviors. Most known livebearers are endemic to South- and Central-America and Southeast Asia. But because of the fact that endemic locations seem tropical to a lot of people, livebearers are considered being tropical fish. Well, that's an incorrect statement! Yes, there are tropical livebearers but there are also subtropical livebearers. And even within the tropical zone on this globe there are sub areas that have a subtropical climate. Specifically, certain altitudes won't have the tropical conditions in a tropical global zone. Most livebearers found elsewhere on this globe are mostly feral strains.
By most people most known livebearers are guppies, mollies, swordtails and platies which belong to the Poeciliidae family. However, there are a lot more livebearer species (poeciliid fish and others) which are kept by aquarists. The majority of them are considered being rare livebearers. And most are kept by serious and experienced aquarists.
Most people do keep the cultivated domestic species of the Poeciliidae family at home. And specifically from the genus Poecilia. Poecilia is derived from the greek word "poikilos' which means lots of colors. But I can assure you that not all members of the wild populations within the Poecilia genus are colorful.
In general fish are wether oviparous or viviparous. When fish are oviparous, the females will spawn the eggs. The fertilization can happen internal (true oviparity) or external (ovuliparity).

When it comes to livebearers, they won't lay eggs (oviparous) but have embryonic development within the mother after an internal fertilization. And when the female is due, she'll give birth to  free swimming offspring. 

To most people, livebearers are all alike when it comes to reproduction. But that ain't correct for there are two ways how these kinds of fish reproduce. Most known are the ovoviviparous livebearers like e.g., mollies, guppies, swordtails, platies and so on... But there are also the true livebearers like e.g., goodeids (splitfins). These true livebearers do have a reproduction which is pretty similar to mammals. 
 
True viviparous livebearers like goodeids in the embryonic state are being nourished by the mother through the socalled trophotaenia (or also spelled as trophotaeniae). It's in some way similar to the umbilical cord (placental viviparity) in mammals. These trophotaenia will be shed or absorbed (they'll nourish themselves through the trophotaenia) in the first till two days after birth. These trophotaenia do look like a cluster of small umbilical cords.


With ovoviviparous livebearers, the embryos have no placental attachment and will be totally nourished from the yolk sac. So, the mother does not nourish the embryos,she's just a safe place before the eggs will hatch. By the time that the mother is ready to give birth, the eggs will hatch. and the fry will pop out of the female's body.
Mostly they're curledb up when they leave the mother's body. But sometimes when it takes a bit longer before fry can leave the mother's body, the rear end of the fry will come out first.
The fry do have a big belly. They'll nourish themselves the first till two days after birth with that what they've stored in their belly. And then they'll slim down and then the'll look for food themselves.
A lot of livebearers are known to reproduce well in captivity. There are exceptions to this rule and some livebearers are very hard to breed in captivity. They might require particular circumstances in order to get them to breed. If the right conditions are not given to them, some female livebearing species will often miscarry, give birth to the embryos too soon or even absorb the embryos.
Since the male livebearer has to fertilize the eggs internally, all male livebearers have an anal fin and this has developed into a reproductive organ that can be inserted into the female. With males of an ovoviviparous species, the reproductive organ is called "gonopodium". Males of a viviparous species e.g., from the families "Goodeidae" and "Hemirhamphidae", the reproductive organ is called "andropodium". Note that the andropodium is just a sort of notch on the front part of the anal fin.
One of the main differences between the two male sexual organs is that an andropodium wil fold when the male inserts it into the female, while a gonopodium will flip forward to insert the female as shown in the picture below.
Many people think that keeping multiple kinds of livebearers in one tank will create inbreeding. Most of the time that will not be the case. First of all, when it comes to ovoviviparous livebearers, the shape of the gonopodium of each species does differ.
And the female sexual organ is adjusted to the gonopodium of a male of her own kind. In order to interbreed with another livebearing species, the sexual organs need to be compatible. But if two species are closely related to eachother, the bigger the chance the sexual organs will be compatible.
Are there both genders of two or more different livebearing species in one tank, their first preference is always to mate with one of their own kind if both genders of that particular species are present. Are there just opposite genders of a specific species present, only than it's most likely that a crossbreed with a sexual compatible tankmate of the opposite sex can be established.
The opening of the sexual organs of both genders are called gonopores.
The difference between the global shape of the anal fin between male and female of both ovoviviparous livebearers will be shown by t.
Looking at these pictures shown above, it's obvious that there is a clear difference in the shape of the anal fin of both genders. And also wether it concerns an ovoviviparous livebearer or a viviparous livebearer. So  again, don't think that all male livebearer specimens have a gonopodium. And that not all female  livebearer specimens have a V-shaped anal fin. For that would be a complete misunderstanding!
Early sexing of the genders is possible for a number of ovoviviparous livebeares. For viviparous livebearers it's harder to determine the correct sex at an early stage. Ovoviviparous livebearers that can be sexed at an early age are to be recognized by the shape of the anal fin. The first finrays of a male is slightly bend and of  a female the first finrays are more straight. A bit later the tip of the anal fin of a very young male is a bit pointy and a bit round when it concers a female.But you need to have a good eye for it to recognize it. Also a large number of very young ovoviviparous female livebearers will show a tiny gravid spot already after a couple of days of their lives. But be aware that not all ovoviviparous female livebearers will show a gravid spot (not even when they're pregnant!). But the majority of those ovoviviparous female livebearers will show one.

And to refer to the different shapes of the gonopodium again (a bit earlier I´ve used explicitly "global shape" for even the shape of the gonopodium of almost each ovoviviparous livebearer male differs in shape)... Here are some pictures which show how different those gonopodiums are shaped depending on the livebearer specimen.
If you'd enlarge these pictures, you'll be able to see clearly that gonopodiums do differ in shape from the start to the tip of the gonopodium. This is very essential to the gonopore of the female to enable a mating. This is one of the main reasons why not all ovoviviparous livebearers can crossbreed with another.
Ovoviviparous male livebearers with a long gonopodium won't have a real courtship when trying to mate. For they can oversee the mating attempt. The end of their gonopodium is also more smoother shaped than a gonopodium of a male with a shorter gonopodium. Ovoviviparous male livebearers with a shorter gonopodium do have a courtship to persuade the female to mate and so they can come closer to the female's gonopore. Because it needs more work for a male with a shorter gonopodium, the end of his gonopodium has got 1 or more hooks to have a better copulation. This can be exhausting for some male specimens. Sometimes it can even happen that they get stuck in the gonopore of the female. Which can lead to stress to both male and female. Worse scenario is that they can get injured and it can even be traumatic.

Note: When an anal fin of a young male will develop into a gonopodium, the anal fin starts to change from the third, fourth and the fifth fin ray.
Well, most female livebearers do have a gravid spot. This is the most translucent part of the skin, close to he anal fin and where the sexual organ of the female is situated. Most females do show this spot already a couple of days after birth. It just needs a good eye to spot this gravid spot at such an early stage. Of course, with female livebearers which are very dark based like e.g., black mollies, even with a very good eye sight, you probably won't be able to spot the gravid spot.
Note: I've mentioned that most female livebearers have a gravid spot for there are also species of which the females don't have a gravid spot. 
It's also a misunderstanding that when a female's got a gravid spot, that she must be pregnant. It's a misunderstanding that can be read at a lot of forums. Having a gravid spot does not mean pregnancy by all means. For actually, females are born with it. It takes a bit before they show it clearly to repeat myself. As already mentioned, the gravid spot is the most translucent part of the skin. But when the embryonic state develops with a pregnant female, the skin will stretch more and more and so this part of the skin becomes more translucent. What we call the dark gravid spot is basically nothing more than developing embryos that will shine through the translucent gravid spot. And that's why it seems to get darker. At a certain moment you'll be able to see those eyes of the unborn fry through the female's skin.
Another phenomenon that may occur with xiphophorus strains (mostly platies), is that a juvenile male is devloping a socalled "pseudo gravid spot". In general the pseudo gravid spot shows up during the transformation of the anal fin into a gonopodium or after the gonopodium has been formed. The pseudo gravid spot develops in the upper layer of the skin (there are 3 layers) which is totally different than the gravid spot of a female. A pseudo gravid spot hardly shows up before the transition of the anal fin. This has got nothing to do with a female turning into a male. For that's a complete other story.
Note: When a pseudo gravid spot shows up on a male's body, it will never dissapear.
Above: An adult male Xiphophorus evelynae with a pseudo gravid spot.

Another misunderstandig is that you'll need a male:female ratio of 1:2 or 1:3 at all times. The socalled harrasment behavior of males goes for just a certain number of livebearers. And most of the times, you see this happen with a certain number of cultivated domestic species. There are a lot of livebearers which can be kept without a problem at an 1:1 ratio in a tank.
For instance, do all male guppies harrass females? No! Definitely not! There are a lot of wild but also fancy guppy strains which are just fine at a ratio 1:1. The problem overhere is that over the years we've been taught a simple rule which we've been generalizing over the years for all guppies (also other livebearers of course). Experienced serious aquarists and breeders do know that this generalization is at hand. Unfortunately, this rule and so many others have been copies of statements that someone made up once just to ensure to put the harassment to a low level and we've been continuing these rules as being true.
Reproduction:
Although, a number of male livebearers tend to chase females all day... that doesn't mean that a mating will take place. Eventhough, a male is trying to use his sexual organ. For it's the female who decides if a mating will actually happen.

If a mating does happen, depending on what kind of ovoviviparous livebearer it concerns, the female is able to store sperm in packages for a certain time period. This means that when a mating has happened that the female does not have to be pregnant. She'll decide if she let's a sperm package fertilize her eggs. And only if that happens, she'll be pregnant. The time period of sperm storing can take as long as over a year. So, not just a couple of months as some like to claim. But I do have to mention that the longer those sperm packages are stored, the lesser the quality of the sperm will get. This all means also that such a female can become pregnant multiple times, from 1 -7 times (mostly less). So, not maximum 3-4 times as I do read from time to time.

The sperm packets are stored in the folds of the fallopian tube (uterine tube). While the female is having this facility and the used folds are random, you'll never know which sperm packets she will use to fertilize her eggs. So, it could be of an older mating or a recent mating. is she having a huge number of eggs, multiple sperm packets will be used to cover the number of present eggs. This means that the offspring of one batch could be fathered by one or more males. If someone likes to linebreed, this is very important to know. That's why virgin and clean (no sperm packets stored anymore) females are so important to use when linebreeding is at hand.

And again, the female is the one which decides wether a sperm packet will be used in order to establish a pregnancy. That's why a female is not pregnant at all (even is she's big because of the present eggs) if she's carryingeggs that are not fertilized yet. So, there are big bellies with developing embryos and there are big bellies with just eggs! And therefore the remark that "female ovoviviparous livebearers are always pregnant" should be considered being a false statement.

It will also take only a couple of days after fertilization that an embryo has fully developed. The rest of the gestation time (depending on the kind of livebearer between 3 - 8 weeks) is needed to let the fully developed embryo grow in the egg. The eggs were already provided by the mother with nutrients through follicular epithelia prior to any fertilization (this is called "pre-fertilization").
Sometimes you're able to watch how a pregnant female that is due that she releases eggs instead of fry. Or even eggs and fry. This means that there wasn't sufficient nutrients in the egg yolk. Because in normal conditions all eggs have sufficient nutrients in the yolk. Which also means that the embryonic development of all embryos is at the same pace. A situation when a female is stressing a lot, you'll be able to see the undeveloped eggs coming out first. For they are easier to push out. Those eggs just didn't have sufficient nutrients in the yolk. So, undeveloped eggs have got nothing to do with stress itself. Those eggs would have never developed as being normal embryos starting from the beginning.
The way fertilized eggs develop untill birth with ovoviviparous livebearers is called "lecithotrophy". So, there's no maternal care. The mother is just a safe place for the embryos to develop and to grow. Nothing more...

Overhere some photos of an undeveloped egg which had just insufficient nutrients in the yolk. Just some eyes are visible and a bit more (propably the head). The rest is fluid. This abondoned egg measures 3 mm in diameter. In the first and second picture you'll see a just released fry and an undeveloped egg. This concerns a batch of a green swordtail.
The undeveloped swordtail egg measures 3 mm in diameter.
Note: The diameter of each egg can differ, no matter the size of the female of each ovoviviparous female livebearer. Which means that also eggs of each batch of the same female can differ in size.

The sperm storage ability goes only for most ovoviviparous livebearers that are lecithotrophic without superfetation and with superfetation. Viviparous female livebearers however have a placenta and don't have the ability to store sperm packets. With pregnancies, the developing embryos are fed through the mother's body (through the placenta) until the actual birth will take place. This method is called "matrotrophy".

But as I've already mentioned "depending on what kind of ovoviviparous livebearer it concerns", means that not all ovoviviparous female livebearers are able to store sperm. Those ovoviviparous female specimens that can't store sperm and the true viviparous female livebearers, do need a new mating in order to start a new pregnancy. So, a resumé: Not all female livebearers are able to store sperm packages!

There's also another way of reproduction with a certain number of livebearer species. The superfetative livebearers. Superfetation means multiple pregnancies with embryonic development in different stages. Such pregnant females will drop 1-3  fry every single day or 2-3 days during a period of approximately 10-14 days. It's also a different way of sperm storage. Sperm from one mating is only used for one batch of fry during this labour period of 10-14 days. So, a new mating needs to happen in order to establish a new cycle of pregnancy. In this case the pace of development is only at the same pace for each individual small group of embryos but not at the same pace as another small group of embryos that such a female is still carrying.
What's also remarkable is that placental pregnancies of superfetative female livebearers (which most superfetative female livebearers are) is also causing that such females start showing bigger bellies later than lecithotrophic females. The hypothesis is that it's got to do with the pace of the waterflow, so that such females are able to swim better with a higher water current for a longer time period.

A unique reproduction method is gynogenesis. It's a bit similar to parthenogenesis but with parthenogenesis it involves the development of a female sex cell (gamete) without fertilization. But with gynogenesis, insemination of an ovum (egg cell) is needed to activate the development of the egg but without the fusion of sperm and the egg nuclei. Which means that the genetic package of the male will not be passed on and so the gynogenetic embryo develops at the expense of the ovum nucleus only. Because of this reproduction method, the fish are asexual (only females). And while the genetic input of a male is of no longer value, the offspring will naturally be all female and identical clones of the mother. 
Because of the fact that such fish are females, they need to use sperm from a male related to their own species. A good example of a livebearer which reproduces itself by gynogenesis is the Poecilia formosa also known as the Amazon molly.

Sex determination:
The majority of animal species can be specified as being bisexual. The genome is in general responsible for deciding wether an embryo will develop as being male or female. A series of developmental sequences are initiated by the sex determination genes which will result into a male or female phenotype. These developmental sequences are called "sex differentiation"and which are controlled by gonadal hormones. Sex determination itself is controlled by genes. Male or female phenotype is controlled by so many mechanisms like e.g., the ratio of X chromosomes to autosomes (any of the numbered or nonsex chromosomes of an organsim).

Sex change:
Overhere a quotation of a paper of Prof.,Dr.rer.nat.,Dr.h.c. Manfred Schartl that will explain the sex chromosomes that Xiphophorus species have. Xiphophorus species have besides the sex chromosomes "X" and "Y" also the sex chromosome "W" unlike other ovoviviparous livebearers. The paper was received on December 19th 2003; received in revised form on February 2004; accepted March 3rd 2004.

Qoute of "Mechanisms of development- Sex determination in platyfish and swordtails":
The quote "Another modification of the XY system was found in X.nigrensis. In this species all XY fish are males. There is an autosomal locus with two alleles, A and a,which affects sex determination in XX fish. If the genotype is AA, the fish will be female, and if aa, the XX individual will be male. Aa genotypes are predominantly female, but sometimes (approx. 5%) such fish develop into males (Kallman, 1984)" goes also for other kinds of swordtails. Which explains the sex change in swordtails and platies (same genus). And as fas as experience have shown, these transformed females will become complete functional males.

Anatomy:
Overhere an overview of all fins of a male and female ovoviviparous livebearer.
A "majority" of the livebearing species will prefer alkaline water where the pH is between 7.0 and 7.8. In general, the water should be hard or medium hard.