Hot Water Fish

Killi fish


When we talk about Killi fish, Killis fish or Killisfish , we are not talking about a fish, we are talking about a family of fish, specifically we are talking about the oviparous Cyprinodontiformes, leaving aside the viviparous Cyprinodontiformes, the famous Mollies , Platys or Guppys .
This division is not very orthodox, from the scientific point of view, but nevertheless Killis fish associations exist all over the world , so there is a real fever for the Killi fish.


When we talk about a group of fish, as varied as the Killi fish are, we can find a great variety of sizes, appearance and color of the fish.
Killis are divided into at least 10 families of fish, with 65 genera and some with more than 100 different species of fish.
The sizes of the Killi fish can measure up to 7 centimeters, although there are much smaller species of Killi fish and others that can exceed these dimensions.
There is also no uniformity in terms of their body shapes, there are Killis with a cylindrical and elongated body, while others show a laterally flattened body.
There is a really curious variety, which has a lance-shaped tail fin, while in the vast majority the tail fin is more rounded.
A common morphological characteristic is that they have a protractile mouth, in which small teeth are arranged, which run through the jaw and pharynx.
What most Killi fish agree on and what has undoubtedly given them great popularity is their color, they are very attractive fish, with vibrant colors.
We can distinguish that there is sexual dimorphism, quite evident between males and females.
It is easy to differentiate males from females, because they have a greater number of colors, or are present in a more intense way than in females.
Another useful morphological aspect to distinguish between both sexes, we have it in the caudal and anal fins, much more pointed in the males. Not to mention size, males differ because they are larger.

Distribution and habitat

Killis are distributed almost throughout the world, with a huge variety of habitats. They are absent in Oceania, North Asia, and Northwest North America.
We have the Cyprinodon macularius that lives in the California desert and that supports temperatures of up to 52ºC, while we have the Fundulus that lives in Canada and supports temperatures below zero.
Killis produce eggs capable of withstanding dry spells of up to two years, even longer in some species.
This particularity can also explain the Killisfish phenomenon, since lovers of these fish can exchange eggs with a simple postal package.

Aquarium conditions

Continuing with the thread of the article, the great variety of existing Killis fish would make it necessary to adapt the aquarium to its correct habitat.
However, we can venture some general characteristics, which could be used for a great variety of species, the most commercial ones.
As we are talking about small fish, we do not need an excessively large aquarium, 50 liters would be enough.
There are species with jumping tendencies, in this case the aquarium should be covered, to avoid greater evils.
It is a great idea to include enough plants inside the aquarium, to generate natural shelters, and that the fish can hide.
The water temperature should be around 18ºC and 26ºC, with a pH between 5.5 and 7.
The Killis like the aquarium water to be renewed frequently. We must remove at least 50% of the aquarium water, once a week.

Aquariums by size

  • Small aquariums
  • 10 liter aquariums
  • 20 liter aquariums
  • 30 liter aquariums
  • 40 liter aquariums
  • 50 liter aquariums
  • 60 liter aquariums
  • 80 liter aquariums
  • 100 liter aquariums

Aquarium type

  • Complete aquarium kits
  • Nano aquariums
  • Prawns
  • Aquariums for Bettas
  • Tortugueros
  • Aquariums for kids
  • Farrowing
  • Cheap aquariums


  • AquaLed
  • Tetra


They are fish that feed almost exclusively on live prey in the wild, but in the aquarium they not only admit live prey, they can also be fed with frozen products, such as red larvae or brine shrimp.
Some hobbyists include highly chopped chicken liver in their diet, which is usually to their liking.
You have to be careful, and the leftover food should be removed to avoid problems and diseases.

Everything you need to maintain your aquarium

  • Best digital pH meter
  • Best Aquarium Test
  • Best anti-algae
  • Best bacteria for aquarium
  • Best siphoner for aquarium
  • Best Aquarium Water Clarifiers
  • Best reverse osmosis filters for aquarium
  • Best UV lamps for aquariums

Behavior and compatibility

Most Killis species are annual, meaning they only live for one year.
When they are fry and very young, they are sociable and have no problem sharing space with other specimens.
As their biological clock is activated, some species become more aggressive, trying to guarantee their survival and that of the species.
When the spawning season arrives, the males will try to protect their territory from other congeners, they become more aggressive.


In the reproduction of Killis, a distinction must be made between annual species, which bury their eggs in the substrate, and non-annual species, which lay their eggs stuck to plants.
The spawning of the annual species occurs in a 15 to 20 liter aquarium , where several pairs of the same species are introduced.
The bottom is covered with boiled peat, which will serve as a nest for the pairs.
Females usually lay a few eggs each day. The substrate is removed every two weeks and placed in bags, which will be kept at a temperature between 15ºC and 25ºC, until we place them in their final aquarium.
Once a month it is checked how they are developing and how much they need to hatch.You can tell that little is missing, when you can distinguish the black eyes of the fry.
The fry that have consumed their yolk reserve are fed with Artemia nauplius.


The variety of Killis out there makes offering concrete advice very difficult.
Perhaps the best advice I can offer you is that if you are interested in learning more about the Killi fish, head over to the Spanish Killis Society, Sek: .

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