How Big are Swordtail Fry?

By Nadine Oraby | 2020 Update

If you have pair of swordtail fish, you need to prepare for a new batch of fry every month. Don’t worry, they may be big in number, but they aren’t that big in size.

How big are swordtail fry? An average swordtail fry can be around ¼ inch (5mm to 7mm) in size. They are roughly the size of a guppy fry. They can grow up to 38mm or 1.5 inches in three months. By this time, they are mature enough to breed.

Swordtail fry may be small but they are easy to spot once they have popped. However, if you fail to see them in the tank, there can be several reasons. For details, keep on reading!

Swordtail fry are never too small for the naked eye

A swordtail female can give birth to as many as 80 fry at a time. While 5 mm or ¼ inch is big enough for the naked eye, you can use a magnifying glass to find them easily.

If you can’t see any of the fry after the mommy has given birth, there are can be two reasons. Either they are eaten by other fish or they are hiding to avoid being eaten.

Indeed, a fry is small enough to be eaten by other fish in the tank, and that can include their own mother. If you aren’t already aware, swordtail fish is an omnivorous species. Fry is actually their favorite food and they don’t even care if it’s their own offspring. If you haven’t taken proper measures, chances are that all those babies will be gone within a few weeks.

By taking proper measures, I mean setting up a breeding tank or trap, and removing the mother as soon as she has given birth; you can save the fry from dying in this uncertain period of their lives. Normally, the fry will become a juvenile in around four weeks. This period varies from fry to fry. With adequate water conditions, four to six weeks is a good average.

Once they become juveniles, they are big enough to survive on their own. However, even at this stage, adult fish might show some aggression towards them. The best way to keep your little ones safe from this kind of bullying is to plant some heavy greens. This will give the babies hiding spots to avoid harassment.

If you can keep them safe from the predators until they are big enough, swordtail babies have a higher rate of survival as compared to other pet fish species.

4 Tips to Make Fry Grow Faster (Video)

Wait for Your fry to grow big enough

Size is important for swordtail fry for many reasons. As you know by now, fry are not safe with their parents and must be kept separately till they are big enough. Now by big enough, I don’t really mean the age.

Yes, ideally your swordtail should be big enough in 4 to 6 weeks, but things aren’t always ideal. There are many factors that may limit or slow down their growth. There is a chance that your fry won’t be big enough to be transferred to the main aquarium even after 6 weeks!

It’s easy to tell. Notice if they are larger than the size of an adult swordtail’s mouth. If they are, then they would be safe in the community tank. If not, then they will still get eaten.

That is why it is important to make sure their growth is as fast as naturally possible. There are many factors that can affect the rate of your fry’s growth. Now, let’s discuss those one by one.

Water conditions affect the growth of a swordtail fry

Your seller will tell you that swordtail fish is a resilient species. To an extent, I agree to that. That sword may not be functional, but this fish does know how to survive. Their rate of survival is better than other live-breeding fish. They can survive not-so-adequate water conditions. However, it doesn’t mean they aren’t affected by it.

Water conditions can definitely affect growth. If they aren’t what’s ideal for swordtail fish, the growth will be slower. Ideal conditions mean temperature between 64 to 82°F with a pH between 7.0 to 8.3. Also, swordtail grow better in water with hardness level of around 12-30 KH.

It may take them more than six months to reach their full size as fries i.e. around 1.5 inches for female and 2 inches for male. If the conditions are suitable, they may not grow to that size at all. So, if you want your swordtail fry to grow fast, make sure the conditions are right.

Feed them properly to support fast growth

Of course, you want to transfer the fry into the main aquarium as soon as possible. You first need to make sure they are grown enough. This may take some time if the aforementioned conditions aren’t properly met. Another factor that can affect their growth is the food.

Remember, like their parents, swordtail fry are also omnivorous. They are ready to chomp things up as soon as they are born. They do not need any assistance from their adults in this regard. The best thing you can feed them is live food. Brine shrimp and egg yolk are great options for proper growth of your fry. Also, they need to be fed more frequently because they won’t eat a lot in one go.

Give your swordtail fry room to grow

I know swordtail fish is generally considered a perfect community tank species. But do you know it is actually a fast water fish? In its natural habitat, a swordtail can grow as big as 6 inches. It is mainly because they get enough room to grow that big. While the store-bought variety usually doesn’t grow any bigger than 2.5 to 3 inches, the size of your tank can determine the size of your fish considerably.

Many swordtail fish owners have told me that they notice slower growth when the fry are in a smaller breeding tank or trap. The best way to ensure proper growth is to have a separate large aquarium for the fry. Not as big as your main aquarium but something bigger than the breeding trap, at least.

If you have a 20-gallon community aquarium, which is the minimum size for swordtail in my opinion, try to get a 10-gallon one for the fry.

Related questions

How can you tell the gender of a swordtail fish fry? You cannot tell the gender of a freshly born fry. All fry look like female fish until the male grow a sword as a distinct anal fin. Some fish grow that tail in just 6 weeks while some take more than three months.

What is the lifespan of a swordtail fish? In an aquarium with proper water conditions, a swordtail’s lifespan is around 3 to 5 years. It is longer for the wild variety that lives in fast flowing waters. Sometimes an aggressive species in the tank can kill peaceful live-bearing fish such as swordtail.

Can swordtail fish breed with other fish? Like most classic live-bearing fish, swordtail fish can breed with other fish such as platies and black mollies. Contrary to popular belief, swordtail fish cannot breed with guppies but they make for peaceful aquarium partners.

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