Killifish are an underrated species that aren’t readily available in local pet stores, but they are among the most beautiful freshwater aquarium fish you’ll find.
They belong to the Cyprinodontidae family, making them distant relatives of the platies, guppies, and swordtails. Killifish are ideal pets to take care of if you’re a beginner.
If you’re new to fishkeeping, it is recommended to start with a single male killifish to gain a better understanding of its specific care requirements.
| Category | Rating |
| Level of Care | Easy to Medium |
| Temperament | Mostly peaceful |
| Appearance | Extreme variation in color |
| Life Expectancy | Minimum 3 months to a maximum of 5 years (depending on the species) |
| Size | 3 to 4 inches |
| Diet | Carnivorous |
| Family | Cyprinodontiformes |
| Tank Size | 10 gallons per Killifish |
| Tank Environment | Modest requirements with a bare floor, minimal lighting, and a sponge filter |
| Tank Mates | Get along well with most species |
Overview of the Killifish
The term ‘killi’ may give the impression that killifish are dangerous, but that isn’t the case. Killifish derived their name from the Dutch word, “Killy”, meaning ditch.
The vividly colored killifish are a diverse group of fish with over 1200 species, including the stunning clown killifish.
They are a hardy species that have adapted to thrive in a wide range of habitats and can be found in almost all locations of the world, except for Antarctica and Australia.
Their preferred habitat is under shallow tropical and subtropical waters.
Most species are mostly freshwater fish, but some species thrive in brackish water and saltwater.
They are found in both moving and still waters. At a natural lifespan of only a few months, the killifish doesn’t live very long in the wild.
Smaller species like the Hummingbird Lampeye and the Dwarf Madeka will attain a length of one inch only.
Larger species like the Orestias cuvieri will reach a span of about 11 inches.
Killifish Appearance
The appearance of killifish varies depending on the subspecies. Almost all killifish have bright and vivid color patterns, displaying strong sexual dimorphism in terms of appearance.
The males are brighter and more ornamented than females. Most killifish a slender, pike shaped body, and flatheads at the top.
The unique shape of their body allows them to swim more efficiently than other species.
Some killifish species have long and broad fins while others have shorter, more rounded fins with a cylindrically shaped body.
All species have a single dorsal fin situated towards the far back on their bodies. Male species attain larger anal and dorsal fins than females.
Are Killifish Aggressive in Nature ?
For the most part, killifish are known for their peaceful temperament and laid-back behavior in a community of multiple species.
This makes them extremely compatible with peaceful tropical fish species like the neon tetra. It is worth noting that male Killies can be aggressive towards one another if placed in the same tank.
If you plan on keeping more than one male Killifish in the same tank, make sure the aquarium has plenty of hideouts where one of them can seek refuge from their bullies.
Female killifish are not known for being aggressive, so you can keep several of them together as long as there’s enough room in the tank.
Caution: Some killifish are known for getting a little too excited and jump out of the water. This can be deadly to your killifish if you don’t have a tank lid in place, so watch out.
If you’ve got the smaller species, they can slither out of small gaps and catch you by surprise.
Killifish Tank Requirements and Conditions
In this section, we’ll go over the tank requirements for Killifish, try not to deviate too far off the general guidelines if you want to provide your Killifish with a good quality of life.
They can live in a range of climates, temperatures, and habitats, which makes them very hardy.
You shouldn’t face any difficulty in mimicking their natural habitat into the tank settings. The size of the tank ultimately depends on the number of killifish you’re keeping and your reasons for adopting them.
Killifish Tank Setup
Due to their small size, a single killifish can live in a 10-gallon tank. But if you’re opting for the larger species, you’ll have to adjust the tank’s size accordingly.
Most of them prefer to live in long, narrow aquariums with little to no water movement. The ideal tank should contain lots of greenery, liven plants, and floating plants.
Use water plants that thrive in lower light conditions, such as java moss and cryptocorynes.
You can keep the tank bare on the floor, but some owners are known for covering it with dark gravel. Make sure the gravel does not harden the water.
Note: Avoid gravel if you want fish to spawn in your tank. Instead, use peat moss that doesn’t contain fertilizer products and other harmful additives. Provide larger caves, wood, and rocks for your killifish to visit when they feel like it.
Killifish Tank Conditions
Most Killies thrive at a temperature of between 72 to 76 degrees. Use an aquarium heater to regulate the temperature if you live in colder climates.
However, if you own multiple aquariums, it may be much more efficient to heat the whole room.
The pH valance of the tank depends entirely on the species of fish that inhabit it because every Killie has its preferences.
Some species come from hard alkaline waters and others come from soft acid waters. For the most part,
they need a water hardness of around 125 to 160 parts per million (ppm). Some species, like the Nothobranchius, will thrive better in softer water.
In terms of lighting, make sure the tank doesn’t have any bright lights because killies are used to hiding from direct sunlight. Most killies are used to low or no water movement at all.
Pro Tip: Smaller killies are easier to manage than larger species because the waste will quickly build up requiring the owner to frequently clean up after the fish.
A balanced freshwater aquarium will require a filter in place to break down toxins, chemicals, and other organics.
Most fish keepers prefer to use filter wool or a simple filter sponge with a box filter. You might want to use under-gravel filters for larger tanks.
What do Killifish Eat
Most killifish are meat-eaters, and in their natural habitats, their diet involves eating worms, larvae, insects, and crustaceans.
However, some species are known for eating algae. Make sure you can provide live food to your killifish – don’t toss flake food and call it a day! If you’re facing a hard time procuring live food for your killifish, then this species is simply not for you.
An ideal diet for adult Killies include the following:
- Daphnia – most fishkeepers use this as live food. It can be collected from ponds or prepared at home.
- Shrimp – A great source of nutrition for killies. You can also feed them frozen shrimp.
- Larvae – You can collect them from ponds based on availability.
- Tubifex – Can be sourced from local stores. Tubifex worms are a good source of nutrition but may carry diseases. To reduce the risk of diseases being spread to your killifish, rinse the Tubidex worms under cold water.
- White worms – They are a good source of nutrition. Just don’t use white worms as an exclusive food because they can be fattening.
- Black Worms – Easy to get ahold of and a good source of nutrition for killifish.
- Algae – You can easily grow some algae at home by leaving a jar full of water to become green with algae.
Killies will also eat the following types of foods:
- Beef heart
- Fruit flies
- Dry foods
- Paste foods
Pro Tip: Never put your killies on a diet of exclusively one type of food, even if the food is a healthy one.
Many aquarists prepare their own fish food to ensure a proper balance of nutrition for their killifish.
If you go down this route, make sure to closely monitor their diet if you plan on breeding them.
If you have newly hatched killies in your aquarium, try feeding them on a diet of vinegar eels, brine shrimp, grindal worms, and infusoria.
If you give live food to your killifish, they will quickly reach sexual maturity at only 2 months old.
Breeding Guidelines
Seeing a killifish grow into a mature adult is a rewarding experience. It’s really simple to breed adults if you want to witness the process from start to finish.
If you want to breed killies, follow these steps:
- Place the killies for breeding in a small tank. Create a substrate of peat moss and sand.
- The female will lay her eggs under the substrate and completely cover them.
- Remove the two parents from the tank once the eggs are laid
- Provide the eggs with a moist environment for the next 3 months
- Now add water to the tank when the eggs are about to hatch
To successfully breed killifish, you have to form a pair first. This can be done only if you know how to spot the differences between males and females. The main differences between the two are:
- The males are brighter and more colorful
- The females have plain patterns and could be colorless in some cases
As a general rule, the blue, red, yellow, and green killifish are males. The females have a dull color. This is all you need to know if you plan on breeding them.
Now simply place one of the vibrant killifish in an aquarium full of female killifish.
The male will quickly start attracting the females by displaying their colors. Interested mates will respond by following the male to the breeding area. The pair will dig into the peat moss and lay their eggs.
Killifish are known for quickly mating with other killifish. Females aim to lay as many eggs as possible and will try to mate with multiple partners.
Breeding Bowl
To speed up the breeding process, try to create a specially prepared breeding area, such as a small enclosure where spawning can take place.
This way, the fertilized eggs can be reared and collected under improved conditions, through natural and artificial processes.
If you don’t provide a breeding space to your killifish, they will simply lay their eggs at the bottom of the aquarium in the gravel.
It is recommended to create a separate breeding area; here’s what you’ll need:
- Peat moss
- A breeding bowl
One convenient solution is to use a plastic tub. You can get one easily from a local store near you.
Make sure to buy one with a lid. The peat moss can be purchased from a local market or nursery. Make sure you’re buying ‘peat moss’, instead of simple peat.
Cut a small hole in the lid, no more than a few centimeters. The hole should have a max radius of about 2.5 cm.
As a general rule, the hole should allow the fish to easily get in and out without getting hurt in the process. Now take some peat moss and sterilize it by bringing it to a boil. This will kill any bacteria or toxins that could harm the eggs.
Before placing it into the plastic tub, let the peat moss reach room temperature. You could run it under cool water to speed up the process.
Some killifish like to dig deep into the peat moss to ensure their eggs are secure. Others will lay their eggs over the peat moss, barely dug in.
The peat moss you prepared will be ideal for both types of fish.
Once the breeding tank has been lined up with the peat moss, fill it up with water.
To restrict the spread of velvet in the bowl, add 2 tbsp of salt as a precautionary measure. Add a few heavy rocks in the bowl to tether it to the aquarium.
Caution: Before placing the bowl into the aquarium, make sure the peat moss is fully soaked with water.
Once you have prepared the bowl, gently place it in the aquarium.
Don’t worry if parts of the peat moss float out of the plastic box, that’s a common occurrence.
But once the killifish start getting in and out of the breeding space, expect a whole lot of mess. Make sure to clean the bowl once breeding is complete.
How to Hatch Killifish Eggs
Once the eggs have been laid in their place, it’s time to incubate them. You will have to provide the right circumstances to hatch them.
The eggs may hatch as soon as 2 weeks or as long as 8 weeks. Try to keep the temperature consistent around the eggs by covering the peat with a foam box. The peat should be placed in a dimly lit area.
Once your eggs are ready to be hatched, they will resemble eyes. This is a big indication that the eggs have reached full maturity.
If it’s been more than 8 weeks, it could be too late. But you can continue to monitor the eggs to see if they’re ready to hatch. When this happens, do the following:
- Fill a 5 cm deep bowl with water
- Put the peat in this bowl and let it gradually soak up the water
- Carefully break each lump apart
- As the peat stats soaking up the water, it will drown to the surface
- The egg will now begin to hatch
- You’ll see the first fries emerge in just a matter of hours – it could take 2 days
- Wait at least one more week before discarding the peat (more eggs could hatch)
The young killifish will struggle to swim at first, but they’ll quickly get adjusted to life outside of the egg.
Once they’re ready to swim around, you can shift them to a different bowl. You’ll have to look after the fry for 3 more weeks if you want them to survive the first few days of hatching.
Where to Buy Killifish
As we mentioned at the beginning, Killifish are a little hard to come by and won’t be easily available in pet stores.
Stores that do stock them won’t have more than a few species. Most people get their killifish from online stores, hobbyists, breeders, and at auctions.
Make sure your killifish are healthy before buying them, your goal should be to buy the best killifish possible.
Try to see if their appearance matches the description of the species you want to buy. Most species share the same traits making it a little difficult to properly identify them in pet stores.
This is extremely important because each species has its own tank requirements.
Are Killifish Aggressive?
Killifish are peaceful most of the time. But when they get agitated, they’ll get downright aggressive. Some species, such as the Blue Gularis, are better kept alone or with compatible fish that can defend themselves in case of an attack.
Final Thoughts: Is Killifish the Right Fish For Your Aquarium
Killifish don’t have much in the way of special requirements. They are an ideal choice for you if you belong to one of the following groups:
- You’re new to fishkeeping
- You have some experience with fish before
Make sure to only pair the killifish with peaceful mates if you want to start a community of fish.
Did you find this guide helpful? Have you got your own tips to share with us? Let us know in the comments below! We’d love to hear from you!
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