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Why The Killifish Is the Fish You Should Consider Raising?

Are you considering adding a new species of fish to your existing aquarium? Perhaps you are just getting started, and looking for a gorgeous species that will liven up your living space. If so, you should consider keeping killifish.

These fish are some of the most gorgeously colored and patterned freshwater fish. Although they take a bit of experience to raise, you can easily learn how to raise killifish with a bit of proper training. Researching the specific care requirements of killifish – and reading this ultimate guide! – will help you learn whether they are the right fish for you.

The Killifish

Killifish Background

Killifish 1-1
Photo by Peter Maguire

Killifish are almost never sold by the name “killifish,” and are instead marketed under their scientific names. This can make them a bit challenging to find in stores, but they are well worth the extra hassle. The killifish name actually applies to an entire family of fish which comprises over 1250 species – these species are then classified into ten different groups.

This diverse group lives in a wide range of habitats spread all over the world. They are found on almost every continent, with the exception of Antarctica and Australia. They tend to live in shallow tropical and subtropical waters, preferring mostly freshwater. That being said, there are some that can live in brackish or completely saline waters as well. Killifish can tolerate both slow and fast-moving waters, and can even survive in bodies of water that are entirely still.

Unfortunately, in the natural environment, killifish have a lifespan of only a few months. This is largely due to their natural habitat, as they tend to live in temporary ponds and floodplains which eventually give out. However, there are some species that live in more long-term environments and can survive a bit longer.

Killifish, despite their name, are not actually dangerous. Their name is instead derived from the Dutch word, killy, which means ditch.

You can purchase killifish online from breeders or hobbyists – it can be difficult to find them for sale at regular fish or pet stores. Generally, if they do happen to stock them, they will have only one or two different species. You will find a much better variation online.

Whenever possible, only choose healthy-looking fish, and make sure they match the exact description of the killifish species you want to raise. Manty variations look similar, and it’s common for them to be misidentified either intentionally or unintentionally. However, since care requirements differ drastically, it’s important that you understand the nuances between the species and choose your pet accordingly.

Killifish Appearance And Behavior

Killifish 2
Photo by Gersom Monerris

Most killifish are small, only growing to about an inch or two in size. Some larger species may grow up to six inches in length, but you will rarely find any larger than that. The smallest species of killifish include the Dwarf Madeka and the Hummingbird Lampeye, while the largest killifish is the Orestias. This latter species in particular can grow up to ten and a half inches!

They all vary widely in appearance, but all will have bright colors and vibrant patterns. Male killifish are more colorful than the females, who tend to be drabber. Killifish have heads that are flattened at the top, as well as mouths that sit at the tips of their faces. They can also ride underneath. They have curved, pointed teeth that are relatively long, along with round scales and a lack of barbels.

This varies, again, between species, but most killifish are slim and excellent swimmers. There are some that have bodies that are rounder, possessing shorter fins, while others have long, broad fins. The body type varies depending on the species, as you can see, but all will have dorsal fins that are placed towards the back of their bodies. Most males also have large anal and dorsal fins.

Killifish tend to be peaceful species and can thrive in community tanks, but it’s important to recognize that the males have a tendency to be aggressive toward each other. This isn’t true of all killifish species, but it is true of most. They tend to live in dense populations, in which dominant males will defend a given territory to allow females and juvenile males to pass through the area.

This varies in captivity, where territorial behavior will be unpredictable and based mostly on how you have your killifish groups. There can also be some variation between individuals. You can generally keep multiple killifish together in an aquarium as long as you have no more than three males.

If you want to keep a larger group of killifish in a tank – which is recommended, as a small amount of killifish species prefer to shoal – you can do this, just make sure you provide plenty of natural hiding places and retreats. You can have multiple females together, but you should try keeping more than two or three similar-looking male species.

You can keep killifish with a range of other fish, particularly those that are peaceful and require similar water conditions. Good options to consider include tetras like Neon Tetras and Rummy Nose Tetras.

Killifish have a tendency to jump, so you need to make sure you cover your tank with a well-fitting hood. Make sure it is secure and does not have a lot of large gaps. Because killifish are small and agile, they can easily leap through very small openings in the lid.

Killifish Tank And Water Requirements

Killifish 3
Photo by Peter Maguire

Killifish have a broad habitat range in the wild, so it would make sense that they are quite hardy and resilient to most conditions in the tank setting, too. Research the individual tank and water requirements of your particular killifish species before determining the best possible set up for you tank, but know that much of how you arrange your tank will depend on how many fish you want to keep. Whether you choose to keep your killifish in a freshwater or saltwater tank, for instance, will also depend on the species.

A twenty-gallon tank is all that is required for a pair of killifish, but if you are interested in one of the larger species of killifish, you may want to invest in a slightly larger tank. Killifish can be kept in shallow, long tanks with little water movement required. Again, you can base this on the needs of the other inhabitants of your tank.

The water conditions will vary depending on the species of killifish you select. Most require water temperatures between 70- and 75-degrees Fahrenheit. You can use a regular aquarium heater to accomplish this. pH needs will also change depending on the species you select. Some prefer waters that are naturally soft and acidic, while others like harder, more alkaline waters. Generally, a water hardness between 120 and 160 ppm is acceptable for killifish.

Water hardness is not as vital to killifish health as is pH balance. That being said, there are some that require softer or harder water for breeding or other specific activities.

Lighting, too, will vary depending on the species, as some are used to being shaded from direct sunlight while others need more light. In general, a tank with low lighting is appropriate for killifish, but you can always adjust this as needed.

You don’t need a lot of water movement, but a filter is essential – particularly if you don’t plan on conducting regular water changes. Killifish are generally kept in small tanks, making them easier to dirty than larger ones. A filter will help keep your tank clean as it breaks down toxins. You can use a simple box filter with a filter sponge or filter wool to do this, or, if you have a larger tank, you can use an under-gravel filter. Your killifish will not disturb the filter.

Decorating A Killifish Tank

Killifish 4
Photo by Peter Maguire

You should include plenty of plants in your killifish tank. Good options include live plants, ideally those that are floating. You might consider cryptocorynes, which is a good plant for killifish because it can thrive in low levels of lighting.

Cover the bottom of your tank with dark gravel, ideally a type that will not harden the water. If you intend to get killifish that are natural bottom spawners, use fertilizer – or additive – free peat, or skip the substrate altogether. Killifish do just fine with nothing on the bottom of the tank.

Make sure you provide plenty of hiding places for your killifish, too, particularly if you have multiple males. You can use floating plants, driftwood, rocks, or other store-bought decorations like castles or large structures for this purpose.

What Do Killifish Eat?

Killifish 5
Photo by Peter Maguire

In the wild, killifish are mostly carnivores and eat a varied diet that includes foods such as worms, crustaceans, and insect larvae. A few species of killifish are omnivores, and will eat algae in addition to the aforementioned meat-based foods.

You should feed killifish live foods in the aquarium, and they will rarely be able to transition to flake or pellet foods. This is part of the reason why killifish can be so challenging to raise. You need to keep their dietary requirements in mind when you make the decision to raise killifish.

A nutritious and varied diet is critical, particularly if you plan on breeding killifish. You can make your own food or purchase it from the aquarium hobby store, but keep in mind that there are certain foods which will fit best in a killifish diet.

Adult killifish can be fed brine shrimp, which are a good source of nutrients and are the most easily eaten by killifish. These can be fed fresh or frozen. Daphnia is another popular choice. It should not be used exclusively as a food source, as it can serve as a laxative, and it should be fed live (not frozen). You can collect your own daphnia from a pond, but make sure you don’t bring any other organisms or bacteria into the tank with it.

Mosquito larvae is another common choice for feeding killifish. You will likely have to collect this food on your own by scooping it out of ponds. This is only available on a seasonal basis, but you can culture it by leaving a container of water to create algae. Be careful, though, as it’s easy to accidentally breed mosquitoes this way.

Tubifex worms may be an easier choice than mosquito larvae, as these can be purchased from most stores and are an excellent source of nutrition. That being said, they can carry disease, so make sure you choose a reputable source and always rinse the worms under cold water to prevent accidentally spreading an illness to your fish. As an alternative, black worms are similar to tubifex worms and provide excellent nutrition, and are bred commercially by many people so they are easy to find.

You can also feed your killifish foods like white worms, fruit flies, paste foods, dry foods, and beef heart. A variation of all foods listed is ideal, which will provide your killifish with plenty of nutrients, vitamins, and minerals. If you are feeding killifish fry, you can choose foods like recently hatched brine shrimp, grindal worms, infusoria, microworms, and vinegar eels.

Killifish Tank Mates

Killifish 6
Photo by Peter Maguire

Because killifish are small and not terribly predatory, you can keep them with a wide variety of tank mates. You will likely need to look up your particular killifish by its scientific name to determine whether it will fit in well with your existing aquarium because, again, there are thousands of types of killifish, with some adapted to saltwater and others preferring freshwater habitats.

That being said, killifish are best kept with tetras such as Cardinal Tetras, Neon Tetras, and Rummy Nose Tetras. Other god options include the Orange Lyretail, Dwarf Gularis, Endlers, and Gardners. Generally, any peaceful fish is fine to keep with killifish.

You should avoid more aggressive fish and you might want to avoid those that are surface-dwellers or long finned. You should also avoid any fish species that can disrupt the process of egg laying and breeding, particularly creatures that have a tendency to sift through the substrate where the eggs will be laid.

Common Killifish Diseases

Killifish 7
Photo by Peter Maguire

Killifish are not prone to very many diseases, but one of the most common issues that arises in the wild has to do with a certain type of fluke. This fluke infects the killifish and causes it to swim near the surface of the water, which they usually avoid in order to prevent being eaten by predators. Swimming at the top of the water column exposes their reflective bellies to predators from above.

You are unlikely to find this disease in the tank, however, but you do need to make sure you avoid exposing your killifish to other common aquarium diseases. The most common reasons for exposure and susceptibility to disease in killifish include severe pH water changes, severe temperature changes, water pollution, fish incompatibility, and poor feeding practices.

Use a pH test kit to monitor the quality of your water. Keep in mind that younger killifish are more sensitive to changes in pH changes than are adult fish. You need to gradually introduce new fish to the tank to limit the impact of the shock on their systems.

Bacterial infections are not uncommon, and usually are brought on by injury or parasitic attacks. These can usually be viewed around the body, fins, mouth, and gill plates of the fish, typically appearing as fuzzy white patches. Fungal infections are rare, but bacterial infections, which look much like fungal infections, are common. You will likely need to treat your fish with an antibacterial agent and quarantine it to prevent the likelihood of it spreading.

Bacterial infections are usually caused by poor water conditions. You may also find that parasites arise as the result of poor water quality or even by the introduction of contaminated food or already infected fish. Parasites are usually visible to the naked eye, and while they don’t typically hurt larger fish, they can harm or even kill small fish. You will need to purchase an over-the-counter ointment to treat a parasite outbreak in your tank.

While you can’t control all of these factors, regular water changes can prevent and easily control most issues. Conduct changes at least once a week, removing only ten to twenty percent of the water at a time to prevent shock. When you introduce new fish, quarantine them for at least two weeks to ensure that they don’t have any diseases to transmit, and rinse live foods before you feed them to prevent parasites from spreading.

Breeding And Life Spans Of Killifish

Unlike most freshwater and saltwater aquarium species, killifish are shockingly easy to breed. This is one of the most common reason why people raise killifish, and why they are so popular. There are two reproductive types of killifish to be aware of for breeding success: the annual killifish and the non-annual killifish.

In the natural world, the annual killifish will live in a body of water that is not permanent – think temporary ponds or gullies. This body of water will dry out each year, killing the fish. Therefore, these fish only survive for a few months at a time, and need to be able to grow and reach sexual maturity in just a few weeks.

These fish lay their eggs in the peat moss. The eggs hatch when the water returns, long after their parents have died. In the aquarium, you can replicate this effect by putting down a peat moss substrate. This will provide a place for the fish to bury their eggs. You can also use sand. You should have them set up in a separate breeding tank so that they are not disturbed by other fish.

After your fish have laid and buried your eggs, you can remove the parents from the tank. Leave the substrate alone, keeping it warm and moist for three months. Add more water after three months, and you’ll see that fry begin to hatch. These annual killifish can live for up to two years in the aquarium.

Non-annual killifish, on the other hand, are those that live in permanent bodies of water that do not dry out. The eggs are allowed to incubate in the water for a shorter period of time. For these fish, a tank that is more sparsely decorated and planted is ideal.

You can use some fine leafed plants, but exercise caution, as you may find eggs stuck inside their leaves that are impossible to remove. If you do use plants, remove the parents after they have laid the eggs, as they will eat the eggs. Non-annual killifish live for much longer than annual killifish, but they will grow and mature more slowly.

Is A Killifish For You?

If you have a bit of experience in the aquarium world and are looking to keep one of the most beloved fish species, whether for breeding or just for entertainment, you should consider raising killifish. These fish are incredibly rewarding to keep, offering months of entertainment and adding vibrant colors to your tank.

As a peaceful species, they cohabitate well with other fish and you don’t need to keep them in a ridiculously large tank. Instead, you can keep killifish with a few other species and have a diverse, colorful tank. If you’re ready to take on the challenge of raising killifish, it could very well be a decision that you will thank yourself for later on down the road.

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