Head to head
Killifish vs Guppy
Killifish and guppies are both small, often brilliantly coloured fish beloved by aquarists, but their reproductive strategies could hardly be more different, one built around eggs that survive being dried out, the other around live young produced on a near-constant schedule.
| Killifish | Guppy | |
|---|---|---|
| Reproduction | Egg-layer; annual species survive drying | Livebearer; gives birth to live young |
| Typical lifespan | As short as 4 to 6 months (annual species) | About 2 to 3 years |
| Breeding effort needed | Specialised; eggs often collected and dried | Minimal; breeds on its own readily |
| Water tolerance | Varies; many need soft or specific water | Wide range, including hard water |
| Colour | Often extremely vivid in males | Often extremely vivid in males |
| Origin | Africa, the Americas, parts of Asia and Europe | Northeastern South America and the Caribbean |
| Population control | Not a typical issue | Can overpopulate a tank quickly |
| Beginner suitability | Better for a specialist keeper | One of the easiest beginner fish |
Killifish vs Guppy: common questions
Which is easier to keep, a killifish or a guppy?
For most beginners, the guppy is considerably easier, since it tolerates a wide range of water conditions, breeds readily and continuously without any special intervention, and is widely available as hardy, captive-bred stock in a huge range of colours. Killifish, especially the annual species from temporary pools, can be more demanding, often needing more specific water conditions, a shorter and more intensively managed life cycle, and, for serious breeding, a deliberate process of collecting and storing eggs through a simulated dry period, making them a more specialised branch of the hobby generally suited to a keeper with some prior fishkeeping experience.
Why do some killifish eggs need to dry out to survive?
Certain killifish, called annual species, evolved in seasonal pools in Africa and South America that dry up completely for part of the year, so the entire adult population dies when the water disappears, and the species survives only through eggs buried in the damp mud. These eggs can enter a genuinely arrested state of development called diapause, allowing them to withstand months of drying, heat, and otherwise lethal conditions, resuming development only once the pool refills with rain, an adaptation guppies, which live in more permanent water and give birth to live young, have no need for and do not share.
Do killifish and guppies get along in the same tank?
It depends heavily on the specific killifish species, since guppies are generally peaceful, but some killifish, particularly certain larger or more aggressive species, can be territorial or even predatory toward smaller tankmates, including guppy fry, while other, more peaceful killifish species can coexist reasonably well with guppies given adequate space and hiding places. Because killifish keeping is such a varied and specialised hobby with very different species having very different temperaments, anyone wanting to combine the two should research the specific killifish species involved rather than assuming all killifish behave the same way toward other small fish.