8 Different Tropical Aquarium Killifish - Rare & Common

Killifish are a popular addition to many nano aquariums; its easy to see why as Killifish are the most colourful species of freshwater fish in the aquarium hobby.

With more than 1270 species of Killifish documented so far, finding one you fall in love with isn't tricky.

Description

Killifish are egg-laying Cyprinodontiform fish. Their family members include Fundulidae, Cyprinodontidae, Aplocheilidae, Valenciidae and Profundulidae. There are around 1,270 species of Killifish in total, with the most significant family being Rivulidae, containing more than 320 species.

Most Killifish are extravagantly coloured, and most species are easy to maintain and breed in the aquarium. The vast majority of Killifish are 2.5 cm to 5cm in size, with the largest species reaching up to 15 cm. Killifish vary extensively in appearance. However, all Killifish have the following in common: their vivid patterns, bright colours, flatheads, mouths at the point of their face or underneath, and their long, pointed and curved teeth.

The majority of Killifish species have no barbels and round scales, and they are slender and pike shaped, which makes them excellent swimmers. Some individuals have a more cylindrically shaped body with short-round fins, whereas others may have long, broad fins. Body shapes of Killifish vary depending on the species, but they all have a dorsal fin fixed towards the back half of their body. In most species, the males are usually much brighter than females and typically have more prominent anal and dorsal fins.

Natural Habitat

Killifish can be found in freshwater or brackish waters in the Americas, as far north as southern Ontario and as far south as Argentina. You can also find species south of Europe, as far south as KwaZulu, in Africa, South Africa, Asia, the Middle East, and several Indian Ocean islands.

A majority of Killifish can be found in rivers, lakes and permanent streams. Some of these habitats can be pretty extreme; the only natural habitat of the Devils Hole Pupfish is Devils Hole, a cavern at least 299 feet deep, branching out from a small opening on the surface, approximately 5.9 feet by 18 feet wide. Killifish usually live between two and three years.

Some specialised forms live in flood plains and temporary ponds and usually have a significantly shorter lifespan. These species, known as annuals, live no longer than nine months and are used as illustrations for studies on ageing. These individuals include the South American genera ranging from the more tropical Pterolebias, Simpsonichthys, Gnatholebias, and Terranatos and the African genus Nothobranchius to the cold water Austrolebias of Uruguay and Argentina.

Behaviour

A small fraction of species will shoal while most are territorial to varying degrees. Most Killifish are peaceful and get along fine in community tanks; however, the males can be aggressive towards each other. Populations can be dense, and territories can change quickly, particularly for species of the extreme shallows.

Many species live as passive tribes in small streams where the dominant males will defend a territory while allowing females and juvenile males to pass through the area. In the home aquarium, territorial behaviour is different for every individual and grouping. In a large enough aquarium, most Killifish species can live in groups as long as there are no more than three males.

One characteristic of Killifish behaviour that you must know about when setting up your tank is almost every single one of them are excellent jumpers and can get through the smallest gaps. Therefore, you must make sure you cover your tank with a tight-fitting lid and ensure its security.

In the aquarium

In the wild, Killifish live in a wide range of habitats, and most Killifish are also quite hardy; therefore, replicating their natural surroundings into a tank setting isn't too tricky.

The size of the aquarium and set up will depend on how many fish you want to keep and your reasons for keeping them. You don't need a large aquarium to keep these fish; you can house a pair or a trio in a small nano tank. The water needs to fill around 70 per cent of the tank, and the temperature should be approximately 73 Degrees Fahrenheit; a couple of degrees on either side of this can affect spawning activity.

Most Killifish should be housed in a long shallow tank with very little to no water movement. Your aquarium should have plenty of live plants, with the majority being floating plants. Although most people like to cover it with a dark substrate, the tank can have a bare bottom. If you choose to use gravel, you should choose a type that will not harden the water.

It is recommended that you do not use gravel if you intend to get bottom spawners; instead, you may use peat as long as it doesn't contain fertilisers or additives. It would also be better for your Killifish if you provided them with plenty of hiding places; these can be roots of the floating plants, wood or rocks.

The pH balance differs in each Killifish tank because every Killifish has a distinct preference. For example, some species come from soft acid waters, where others inhabit hard alkaline waters. Although for most Killies, a water hardness of 120-160 ppm is suitable, water hardness is not as essential to get right as the pH balance. However, there are a few species that require soft or hard water, such as the Nothobranchius.

The lighting again depends on the individual species; most Killifish prefer shade from direct sunlight and like low lighting tanks.

As for filtration, if you decide to have a small tank, you will more than likely need to use a filter unless you are prepared to do small frequent water changes. Small tanks are easier to befoul than larger ones, as waste products build up quickly. A filter will break down toxins, and the most popular type to use in a small tank is a simple box filter with filter wool or a filter sponge.

Tankmates

Generally, the Killifish have a peaceful temperament which makes them compatible with several fishes. Killifish do well in a tank with other similarly sized fish with the same character. Ideal tankmates for most Killifish are Danios, Smaller catfish varieties, Tetras, Rainbowfish, Rasboras, Apistos and other peaceful fish.

However, if you want to breed the Killifish, it is advisable to separate the breeding pair from the community tank. This is because most species prefer isolation, as well as preventing interbreeding with other killifish species that will form hybrids. Additionally, it would be best if you did not keep Killifish with larger fish species such as goldfish or larger Barbs as they may very well see them as snacks.

Feeding

Killifish are carnivores, and they feed primarily on aquatic arthropods such as mosquito larvae, crustaceans and worms. As a result, they specifically need live foods such as daphnia, bloodworms and brine shrimp rather than frozen or freeze-dried foods as their base, which is another reason why they're not usually a good choice for beginner hobbyists.

Some species of Orestias from Lake Titicaca are microscopic organism filter feeders, where other species such as Megalebias, Cynolebias and Nothobranchius ocellatus are predatory and feed mainly on other fish.

The American Flagfish feeds heavily on algae and plant matter as well as aquatic invertebrates. And finally, Nothobranchius furzeri needs a lot of food because they develop quickly, so when the food supply is inadequate, bigger fish will eat the smaller fish.

Breeding

There are two types of breeding killifish. Some species are annual spawners, while others are non-annual spawners. Females are mild and can be kept in large numbers together, but the males must have plenty of space to prevent aggression towards one another.

Like most fish species, the males are more brightly coloured than females, especially during the breeding season. Killifish are usually reasonably easy to breed when given the correct setup.

If you have an annual Killifish, you will need to keep their natural breeding sequence in mind. In nature, these fish reside in bodies of water that are not permanent. So every year, this body of water dries up, which results in all the fish dying. Because of this, the breeding timeline for the annual Killifish is concise. The Killifish do this by laying their eggs in the moss where it will be safe. The eggs then stay there until the water comes back the following year.

You should provide them with peat moss or sand in their substrate, where they will feel comfortable to bury and lay their eggs. If your fish don't feel like they have a good location for their eggs, it can lead to various issues that may stop the process before it starts. After they have laid their eggs in the tank, you'll want to mimic their environment in the wild by removing the water in the tank.

You will need to keep the substrate warm so the eggs can develop. However, do not let the tank become bone dry; a little moisture is required. After around 90 days, you will need to add water back into the tank so the fry can hatch. Once the fry hatch, they will consume their egg sack, and once this is gone, you should then feed them brine shrimp.

Non-annual Killifish are much more straightforward to breed. Also, unlike the annual Killifish, non-annual Killifish don't have to go through the nightmare of having their home dry up every year.

The breeding process for these Killifish is pretty standard. However, it would be best to make sure that there are not too many things in their tanks, such as plants or decor, to replicate the areas where they would be laying their eggs in the wild.

The eggs incubate in water for a much shorter period than that of the Annual Spawners. Therefore, you should ideally remove the parents soon after they have laid eggs to avoid them consuming them. In addition, the growth rate is much slower than annual Killifish; however, they live longer.

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