How big do Killifish get?

By Nadine Oraby | 2020 Update

I recently planned to get a killifish, so I got curious about their size and came across some interesting information that I would love to share with you all.

So, how big do killifish get? There are different species of killifish that are small in size and the rest are bigger. However, the average size of a killifish is known to be 2- 3.5 inches in length but they can also size up to 6 inches depending on different species.

Let’s elaborate on how can one provide the best and suitable conditions for the growth of a killifish in an aquarium so that you can easily take care of them.


It is important to look into significant factors that are as follows:

  • Tank Setup and Conditions
  • Size of the Aquarium
  • Setting up an ideal Environment for Killifish
  • Lighting of the Aquarium
  • The Perfect Diet
  • Behavior and Compatibility
  • Effective Filtration System

Tank Setup and Conditions

Firstly, the tank size depends on how many killies you plan to get! The tank conditions vary as per the species of the killifish as they require different water conditions, water hardness, and temperature and the Ph Level.

Let’s discuss these three in detail,

  • Water Hardness
  • Water Temperature
  • pH level

Water Hardness

It plays a very important role in the health of killifish, especially in an aquarium. For the majority of the killies, the appropriate level of water hardness should be between 120-160 ppm. Some killifish require hard water while few of them require soft acidic water, especially for breeding.

Water Temperature

For killifish, the ideal water temperature should be between 72-75F. Conventional water heaters may be used to maintain the water temperature that is ideal for killies.

pH Level

Every killifish has a different preference, therefore, the pH level may vary from one killifish tank to another. However, the most ideal level as per the majority of killies is between 6.0 to 7.0.

The size of the Aquarium

To accommodate killies, a 20-gallon tank is considered to be ideal for a regular killifish. The size can vary as per the number of killifish to be kept. However, one does not need a large aquarium for small killies, as a trio or even a pair can be kept in a 12x8x8 tank but it is recommended that they are kept in a bigger tank so that they can interact and have fun with other groups.

Setting up an ideal Environment for Killifish

Killies are inhabitants of forest streams, therefore, a heavily planted aquarium is suitable for them, hence live floating plants are recommended to prevent direct sunlight. The most suitable ones are Cryptocorynes, Java fern, and Java Moss. Also, an aquarium with a tight fitting lid is highly recommended as killifish are famously known to be accomplished jumpers.

Lighting of the Aquarium

Majority of the killies prefer subdued lighting because they do well with low levels of light because they are inhabitants of streams, lakes, and lakes. Therefore, lighting should be managed in an aquarium by planting ceiling plants like duckweed so that it is ideal as per the preference of different species of killies in one aquarium.

The Perfect Diet
Killifish are known to be carnivores and require a well-balanced diet that too with variety. They prefer live food over flake food, such as fruit flies, brine shrimp, daphnia, mosquito larvae, tubifex worms, blackworms, and white worms. They can also be fed frozen food.

Behavior and Compatibility of Killifish

Killifish are known to be peaceful and live in small groups. They can be easily kept with other fishes too. However, male killies are known to be aggressive towards each other but one superior male killifish usually safeguards his group. It is important to research beforehand keeping different species with killifish as some such as a Blue-Gularis are better when kept alone.

Effective Filtration System

For Killifish, it is recommended to utilize filtration as well as aeration to maintain hygiene in an aquarium. Installing Air driven filters can play an important role in breaking down of harmful toxins such as ammonia and keeping the aquarium clean and healthy for the killifish. Also, sponge filters and small box type filter are the most commended filters.

Related Questions

Can beginners keep killifish as a pet fish? Keeping killies can be difficult so it is recommended to have beforehand knowledge related to different species and names as keeping them requires a little bit of expertise. Therefore, for beginners, it can be a bit challenging. Killies, however, are known as a rewarding breed to keep and enjoyable too!

Is it okay to keep a killifish with other fishes? Killifish are friendly and can be kept easily in a community aquarium as long as the other fishes are peaceful and have similar preferences for different water temperature and dietary needs.

What is that one thing, one should be careful when keeping killifish? The care level of killifish is totally species dependent therefore one should have knowledge about them. Also, the aquarium should have a hood, as killies are known to be incredible jumpers! Therefore, it is important to keep the tank covered as they have the tendency to jump even through small gaps.

How can one differentiate a male Killifish from a female Killifish? Male Killies are more bright and vibrant such as red, blue and green as compared to female Killies that have a dull color such as brown.

Why should one keep a killifish? There are many reasons to keep a killifish as they add color to the aquarium with their beautiful and vibrant colors and are low maintenance. Also, it is known that there are over 1250 species of Killifish so there are tons to choose from. They are easily adaptable if provided a suitable environment.

Is it easy or difficult to breed killifish? Killifish are the easiest to breed. Before breeding, it is important to be acquainted with reproductive types which are the non-annual and annual Killifish as they both have different requirements.


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