Fish Guide

How Big Do The Killifish Get?

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Although being a beautiful freshwater fish, I have seen that the Killifish isn’t popular as it should have been. I didn’t hear the name of this fish very often, too. How about you? How much do you know about this fish? As for me, I saw that many readers were curious about one question. It is “How Big Do The Killifish Get?”. I wanted to know about this fish by myself too. So, I spent some time on the research. I found out some facts about the gorgeous underrated gem of the aquarium world. Let us get started then.

Killifish are available in tropical and sub-tropical waters of every continent in the world except Australia. There are around 1250 species of Killifish available in the world today. So, the size varies from one another. Nonetheless, most of these fish are small. The size of the smaller fish is between 1 to 2 inches(2.5 to 5 cms). On the other hand, the average-sized Killifish grow up to 6 inches (15 cms). However, there is a species of Killifish that grows up to 18 inches too.

What Do You Have To Know About The Killifish?

Killifish are one of the most beautiful fish in the fishkeeping world. However, many fish hobbyists do not prefer to pet this.

I have seen people who are confused about the name of this fish. What about you? Do you also think the fish got its name because they are killers? Well, you are mistaken if you think so too. This fish got its name from the word Killy (from Dutch). It refers to small beings.

You might also be interested in Easiest Fish To Breed- Beginner’s Guide.

Furthermore, the Killifish is not a starter fish for beginners. The care level of this fish is not that hard. But it is not too easy, either. Do not pet the fish if you are a beginner. Get the experience of at least 1 to 2 years before petting your fish. You need to learn all the basics of aquarium fish keeping.

I have also written an article about A Complete Beginner Guide to Killifish: Care, Breeding, Lifespan, Diet.

How Big Do The Killifish Get?

Like I said earlier, there are around 1250 species of Killifish available today. The size of each species differs from one another. Well, most of these fish are small. The minimum/ average size is between 1 to 2 inches. The larger ones do not grow more than 6-inches too. So, you have got the answer to today’s question. Thus, the maximum growth size is 6-inches (15 cms).

Also read out an article on the Small Tropical Fish That Does Not Require Much Space In Aquarium.

How Long Does It Take For A Killifish To Grow Up to Its Maximum Size?

The Killifish is the fastest maturing invertebrates. These fish grow faster from 5 mm to 54 mm in 14 days. Researchers have said that the Killifish mature fast in the wild. It means these fish grow slow in captivity.

Which Is The Biggest Killifish?

The Gulf Killifish is the biggest fish in the species and grows up to 18 cms. It has a blunt head and short nose.

Which Is The Smallest Killifish?

The smallest Killifish is the Heterandria Formosa. Its common name is the Least Killifish. Get the details about Least Killifish Care: The World’s Smallest Livebearers here.

Size Of The Killifish In Wild V/s In The Aquarium

Like I said earlier, the size of Killifish is comparatively big in the wild. These fish get smaller in the aquarium. It is because of the differences in both the environment. The Killifish can grow up to 18 cms in the wild. However, these fish can grow up to a minimum of 6 inches in captivity.

What Are The Factors That Affect The Growth Of Killifish?

Killifish grow faster when they start maturing. Various factors affect the growth of Killifish besides genetics. The growing process will be even more affected when in an aquarium. The main reasons are the tank conditions, water parameters, diet, and tankmates as well. The captive environment might seem a little awkward for the fish too.

I have also written an article about ‘How many Killifish in a 10 Gallon or 20 Gallon Fish Tank’.

What To Do If Your Killifish Isn’t Growing To Its Required Size?

Is your Killifish not growing well? Don’t worry much. You need to know the reasons for hindering their growth. There might be things that are stressing your Killifish. Let us discuss the things that you should remember.

How To Improve The Growth Of Killifish In Captivity?

The growth of Killifish does not only depend upon the genetic of the fish. The external factors in the aquarium conditions determine the growth of your Killifish too. The care level of Killifish is Easy-Difficult depending upon the species.

Aquarium Requirements

Any fish species require extra care in captivity. You may already know that the care level of Killifish is not that hard. However, do not think about petting the Killifish if you are a beginner. Have an experience of at least 1 to 2 years before you keep Killifish as a pet fish. The first and foremost thing that comes to our mind is tank conditions. Isn’t it?

Tank Conditions

Since most of the Killifish are small in size, you need not keep them in big tank size. Furthermore, these fish are not shoaling fish either. So, do not keep more fish together.

The average tank size is 5 to 10 gallons for smaller species. However, if you are thinking about adding more than one male or larger fish together, then choose a 20-gallons tank.

If you didn’t know, most of the Killifish are peaceful. The females adjust together, but the male can’t tolerate each other at all. So, analyze the size and nature of these fish before choosing a tank size.

Water Parameters

The water parameters vary according to the species you choose. However, the average water temperature is between 68 to 75 degrees Celcius. Most of the Killifish prefer the temperature between 72 to 75 degrees.

The PH balance is different with each species too. But most of the Killifish prefer a PH of 6.0-7.0. The water hardness level is best between 120-160 ppm. Some species prefer hard water while some may not. Let me tell you this, most of these fish prefer soft water during the breeding process.

Learn in detail about How To Maintain Aquarium Water Hardness – Freshwater Aquarium Guide.

Even the little changes in the water parameters can harm your fish. So, one should check the fish species before analyzing the water parameters. It is because the water parameter is one of the most important things for a fish.

Moreover, it helps determine the growth of the fish too. Water has the essential nutrients for the Killifish to help sustain their lives. Not only that, but the correct water parameters help in the growth of your fish as well.

More articles about maintaining water parameters in your aquarium:

Lighting and Heating

The lighting depends upon the kind of species that you wish you keep. Most of the Killifish prefer the shades of direct sunlight. So, those species like subdued or low lighting.

I would suggest hygger 50W Mini Submersible Digital Display Aquarium Heater for your fish tank. 

However, some Killifish prefer moderate lighting as well. On the other hand, it is best to keep a water heater inside the tank. It will keep the water temperature balanced.

Continuous changes in the water parameters may stress out your fish. As a result, it will affect the growth of your Killifish. Aqueon water heater is the best option for these fish.

Is Too Much Water Change Harmful For Your Fish: How To Do It Safely? Find out here.


Furthermore, a proper filtration system is essential for the fish in captivity. It is because these fish produce more waste. All the fish waste won’t have a way to go out on its own. So, keep a filter to purify the water in the aquarium regularly.

Hang-on back Filter is the best suitable filter for the Killifish. Check out our other articles to find about the filtration system in detail. Also, don’t forget to change the amount of water from time to time as well.

A healthy water environment will make your fish happy. Not only that, but it’ll also keep them healthy. You could take help from the expertise of petting Killifish too.

The best sponge filter would be Hikari sponge filters for your fish. It is quite affordable and works best.

Choose The Right Tankmates

Do you love challenges? Well, this one might be one for you too. I mean, about choosing the right tankmates for your fish. These fish are not particularly shoaling fish. You could keep these fish alone as well.

However, these can adapt in a community tank. All you have to do is to choose the right tankmates for them to stay comfortably. So, what are the correct tankmates?

As I said earlier, males get aggressive with each other. You can keep two males if you have a larger tank. On the other hand, females can live with each other. Since there are varieties of species of Killifish, tankmates differ too.

Analyze the nature of your Killifish before keeping a tankmate. Additionally, Killifish prefer the tankmates, which have similar behavior as they have. Right tankmates determine the level of anxiety or comfortability of these fish.

Will My Killifish Eat Shrimp? Find out in our Complete Guide!

A Properly Balanced Diet

Food is an essential factor that determines our growth as well. Yes, your growth depends upon your genes. But sometimes, the right nutrition also helps us grow faster. The same is the case with every living being on earth.

You may already know that the Killifish are Carnivores. These fish prefer eating live food like crustaceans, insect larvae, and worms in the wild.

However, don’t even think about providing frozen food to your fish. It is because your fish may not adapt to such foods. You should provide them with live foods in captivity as well. If you think you can’t, then please don’t pet the Killifish.

Some of the best food products for these fish are:


Now that we are at the end of this article, I hope that I’ve answered all your queries. Make sure you keep your Killifish healthy and happy. Provide adequate love and care to your fish so that it grows up to its required size or maybe more than that. So, Happy Fishkeeping!

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