This is a really interesting question. In short, the answer is no guppies do not lay eggs, but they are of course, not mammals. So what’s really going on with the guppies?
Whereas most of the fish world are egg-layers, laying their eggs once they have been fertilized, guppy fish are known as livebearers. This means that they birth their fry live.
In this article, we will explore guppy fish reproduction. From their mating process to gestation periods, birthing, and all the special tricks up their sleeves to ensure successful reproduction.
How Guppies Mate.
Guppies have earned the moniker millionfish thanks to their astounding breeding capabilities.
With the capability to have between 20-200 fry per birthing and the ability to birth every month, it’s easy to see where the term millionfish comes from. But how does their mating process work to allow for such regular birthings?
When guppies mate, the male fertilizes the eggs by depositing sperm into the female’s reproductive tract. From this, the eggs stored in the female guppy’s several egg sacs can be fertilized.
Only one sac of eggs will be fertilized at a time. Female guppies can store sperm from a single mating encounter for up to a year, allowing them to birth fry every month regardless of whether a male is nearby.
The Gestation Period.
With the ability and desire to produce hundreds of fry every month, the gestation period for guppies is quite short.
On average, guppy gestation lasts from 22 to 26 days. However, it can range from 21 to 30 days. Factors that affect the length of gestation include the temperature, cleanliness, and suitability of the tank, as well as the general health of the guppy.
These are factors that also affect the viability of the fry and are something that should be researched and considered if you are planning on allowing your guppies to breed.
How Guppies Birth Their Fry.
Once guppies have reached the end of their gestation period, they are ready to deliver their fry. Female guppies can give birth to their fry in 2 to 6 hours on average.
Guppy fry are birthed one at a time and emerge curled into tiny balls, after a few moments they will uncurl themselves and start swimming rapidly.
If the fry are healthy, they will swim upwards, if they are not they will sink and are not viable. Guppies will usually take short pauses between the birthing of groups of fry.
However, this process can take a lot longer if the birthing guppy is stressed. In these instances, pauses between groups can last up to twelve hours.
If a guppy is stressed or underfed during the gestation period, it may end up giving birth to only a few fry. If this happens, the fry are likely to be unviable and will not survive long after being birthed.
Instances Where Guppies Lay Eggs.
There are a few instances in which a guppy may lay or dump some of the eggs from their sacs. While this occurrence is rare, it can be a sign that something is not right with your guppy fish.
If you are attempting to breed your guppy fish and notice it laying eggs in the tank, it may need to be checked by a specialist vet to ensure its health and the health of any potential fry. Below are the most common reasons why a guppy may lay eggs.
Fry Is Not Formed Properly
Sometimes the fry do not form properly within the egg, in this instance, the guppy will lay the egg along with the live birthed fry. If you find these eggs in your tank they will be bigger than an unfertilized egg, this is because there is a fry inside.
You may be able to see the fry or even detect some movement inside the egg. These fry are not viable, however, and if hatched from the egg would likely not survive. The laying of eggs with improperly formed fry is a miscarriage.
The Egg Is Not Formed Properly
While the eggs inside fertilized sacs are stored within the female guppy’s body for the duration of the gestation period, sometimes they do not form properly. There are many reasons why this could happen.
The guppy may be stressed, or unhealthy, or the eggs may become infected by bacteria from poor water quality in the tank.
If the latter occurs to fertilized eggs it may cause the death of the embryo inside. In this case, the eggs will be laid at the end of the gestation period along with fully the developed, live-born fry.
The Egg Isn’t Fertilized
Despite a guppy’s apparent reproductive ease, there are occasions when their eggs fail to fertilize despite the presence of guppy sperm. In these instances the eggs are known as ‘dead eggs’ and they cannot produce young.
When a female guppy has dead eggs in her sac she will attempt to release them. If the eggs are successfully released, they must be scooped from the tank and thrown away so as to not affect the quality of the water.
If a female guppy is unsuccessful in releasing the eggs it can cause severe health issues in the fish.
Even though guppy fish are livebearers, their eggs play an integral role in the successful development and birth of their offspring. Healthy guppy fish with healthy fertilized eggs will not lay or release their eggs.
If you have discovered guppy eggs in your fish tank, it could be a sign that something is wrong with your female guppies and should not be ignored.
Similarly, if you do not want your guppies to produce offspring, potentially in the hundreds monthly, it is important to keep mature female guppies separate from male guppies.
If your female guppy is already pregnant or has had offspring or released eggs recently, they could continue to produce offspring for the next year even when separated from males.