How Long is a Tropical Fish Pregnant For?

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In this article, we will talk about fish reproduction in detail. But since there are thousands of different fish species in the world, we will mainly discuss tropical fish. You’ll find out what the gestation period and reproduction time are for different fish species. I will also tell you about the best water parameters that must be met for breeding tropical fish.

Live Bearing Fish Gestation Period

There are certain types of fish, that do not release eggs into the water to reproduce. Instead, they give birth to young fish, who are fully or just partially developed at the moment of birth. This process is very similar to what mammals do.

However, the gestation period could vary from one species to another. Even so, the most common time period is about 4 weeks. This is the time that has to pass from the moment of egg fertilization, to the moment when the birth is taking place.

Note that the gestation period is not beginning when the breeding is happening. That’s because certain fish species can store the male sperm and not fertilize the eggs for months after the mating happened.

Now, let’s see what the gestation period is, for some popular fish types:


Usually, guppies will take between 26 and 31 days to give birth, from the moment of fertilization. So, in most cases 4 or 5 weeks will be the gestation period.


Platys are very similar. In most cases, the gestation period will last for around 28 days, if everything goes as it should. The fry are carried till they become fully developed and that’s when the birth will take place.


The Molly fish will take significantly longer to give birth than the previous 2 mentioned right above. Usually, the gestation period lasts for 60 days. However, they can fertilize the eggs multiple times, because they store the sperm from the male for months. A Molly can give birth to many new young fish (10 – 60 at a time).


Swordtails will spawn new younger fish, after 28 days have passed since the fertilization moment. Noticing the pregnancy is a little more difficult with Swordtails, but the gestation period is almost every time 28 days.

Egg Laying Fish Reproduction Time

Differently from the previous 4 fish species, there are many more that lay eggs in the aquarium to reproduce. When the eggs were placed on the bottom of the tank, they will hatch in a certain period of time. But how long does it take for the eggs to hatch and let the young fish out?

This time period is mostly dependent on the species of fish we’re talking about. Most tropical fish have different egg reproduction times. Let’s talk about 6 of the most popular breeds:

Neon Tetras

They will lay between 60 and 130 eggs at once. But not all of them will hatch (this is normal). You can expect about 50 baby Tetras to hatch from the eggs in a single breeding. When you first notice the eggs on the bottom of the tank, or on the plants, take the mating pair out of the aquarium. Otherwise, they could eat the eggs. It usually takes about 24 hours for the fertile eggs to hatch.

Betta Fish

This species will lay around 500 or 600 eggs in a single breeding. Most of them will hatch pretty quickly, similarly to the Neon Tetras. But keep in mind that a big portion of the eggs could hatch, meaning that even 500 of new Betta Fish could appear in the aquarium. So, before breeding Betta Fish, make sure you have everything set up accordingly, so you can care for all the fry.


Goldfish usually release up to 1000 eggs for reproduction. But don’t be scared. Only a small portion will become fertile and hatch. It takes approximately between 48 and 72 hours for the eggs to hatch, after they were deposited in the aquarium.


They will lay their eggs first and then the male will fertilize them separately. It takes around 24 hours for all the eggs to be deposited. When the pair is finished, the eggs will hatch between 48 and 72 hours.


The Plecos will lay their eggs in caves, so make sure you have at least one set up in the aquarium. When the eggs were released onto the cave’s floor, it will take from 4 to 10 days to hatch. While this happens, the female will guard the eggs from any dangers.


This specie will lay between 40 and 160 eggs in a single reproduction. Most of the time, the egg spawning lasts for about an hour. It will take 4 or 5 days for the eggs to hatch entirely.

Water Parameters for Breeding Tropical Fish

Most tropical fish need well set water parameters when they’re ready for reproduction. Why is this the case? Simply because most fish won’t begin mating, unless the water parameters are set to the right value. By doing this, you can mimic the real conditions your fish would have in the wild.

Otherwise, they might never begin to mate one another. What should you be careful about?

For instance, the water temperature is an important factor. Since we’re talking about tropical fish, they need warm water to live in. But most tropical fish will like to have even warmer water when they’re ready for breeding.

There are exceptions though. Some fish are reproducing in the winter. If that’s the case, you will need to lower the water temperature, to let the fish know, time has come.

Also, keep a look out for the pH level in your aquarium, together with the water hardness. There are fish that like softer waters when they’re ready for mating. Other like the exact opposite. So, do your research, and ensure the best water parameters for the types of fish you possess.

Best Food for Tropical Fish Breeding

The type of food needed for breeding tropical fish is mostly conditioned by your specific fish. There are species that eat all kinds of food (frozen, live, pellets or others) and others that only eat specific food when they begin breeding. So, make sure you give them what they need in this period.

Also, you need to take care of the newly born fry. This is again, different with most species. Some won’t need any food right away; others will eat solid food in the first minute after they’re born.

The idea is, get to know your fish community, before you begin the breeding period. This way, you’ll give them exactly what they need. The food will affect your fish positively, thus making them healthier and the fry will also be healthier from the start.

How to Tell if a Tropical Fish is Pregnant?

You might think it’s hard to tell when a tropical fish is pregnant. But the truth is, most tropical fish species, are very noticeable at pregnancy. Like with most living creatures, tropical fish will also present a bigger belly, when pregnant.

If you have fish that directly give birth to living fry, it will be easier to spot when they’re pregnant. Their belly will grow significantly, quite quickly. The period depends on the species at hand (see above for details).

Also, another method to tell if your fish is pregnant, is to look for mating rituals. Different fish have different kinds of mating rituals. Do a search online to find out about your fish exactly. When you notice that ritual in the tank, it’s a big sign that your fish might get pregnant soon.

If you have fish that usually lay eggs, an important sign for pregnancy is the nesting process. If you see your fish preparing a nesting place, it will soon lay eggs in there. Be prepared in this case, and learn everything you can about caring for the fry.


In this article we’ve talked about tropical fish breeding. You learned that it is done in 2 different ways:

  1. By giving birth to live young fish
  2. By laying eggs that will hatch in the aquarium

There are many tropical fish that are present in one of these 2 categories. Above, I talked about multiple popular breeds that you may already possess.

Later, I mentioned that water parameters are very important in letting your fish pair begin mating. This is actually the most important aspect that influences breeding. If the water conditions aren’t propitious, your fish will never begin reproducing.

The food must also be considered when you let your fish reproduce. Certain food types could strengthen them, while others could get them sick. So, make your choice wisely. And do some thorough research before you buy food for the fry.

All in all, breeding tropical fish isn’t a very complicated process. All you have to do, is abide by the rules for every species. If you do everything right, your fish will give life to healthy fry, that will thrive in your aquarium.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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