Is my livebearer Pregnant?

This question gets asked on this board quite often so I am posting this up top. Please realize that this is not an exact science (much like birth in humans), so an exact determination is not possible. However with some observation on your part you will soon be able to tell about how far along your livebearer is.

Most of the common livebearers: Guppies, swordtails, platies, mollies, endlers, etc belong to the family known as Poecilidae.
I would be suprised if you had poecilid that wasn't "hit". The eggs are developed by the female and then fertilized by the male (or by stored sperm). The fry then develop from the egg without any nutrition from the female other than an oxygen supply. The term used for a female with developing fry is "gravid".
Most poecilids constantly have eggs/fry developing. Under good conditions these fish will drop fry about every 30 days. Under other than favorable conditions these fish can suspend/delay development or even reabsorb the eggs. Since these fish store sperm, once they have mated they can deliver to as many as 7 or 8 drops (maybe more). Size of the female is indicitive of a drop growing closer. One trait that is often a tell for many species is the squaring off of the ventral area of the fish. Many claim that they can tell by the darkening of the gravid spot (which may not be visable on all poecilids especially mollies). The gravid spot is somewhat valid as the darkening is often the eyes of the developing fry, a dark gravid spot is not an absolute indicator however. Some fish don't get dark gravid spots due to their natural coloration. Other fish may have a dark gravid spot all the time. At least one Poecilid, Hetrandria formosa develops fry by a process called superfoetation. Superfoetation is where the female carries fry in various stages of development. At times these fish perhaps drop a fry every 3 or 4 days.

There is another family of livebearers, Goodeidae, that are less common, but sometimes kept in the hobby. These fish require refertilization for each brood. The gestation period is about twice as long as poecilids or 60 days. The females in this group of fish get huge before a drop (you have to see it to believe it) and the fry are born very large. Interestlingly enough these fish do provide nutrition to the developing fry, which is part of the reason they are dropped so large. They fry are delivered with something like an umbilical cord called a trophotaenia.

If anyone has any content they believe will add to this information please PM me and we will look at putting it in.

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