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Today on Animal Fact Files we’re discussing killifish. Get schooled on all kinds of other animals by subscribing to the channel! Killifish have a couple different common names like pupfish or mud minnows; it all really depends on the species - of which there are more than a thousand - and some species don’t even have common names, so for simplicity's sake, we’ll just say killifish are any fish from the cyprinodontiformes order that lay eggs. That does indeed imply that the other fish belonging to that order give birth to live young, but we’ll have to explore that in a future episode!

Some killifish species are found in permanent water habitats such as stream, lakes, and even coastlines. Depending on the species, killifish are quite adaptable to environmental conditions such as heat and cold as well as water salinity. This means killifish are euryhaline because they’re able to tolerate freshwater as well as saltwater - and, yes, that technically means they can handle brackish water, too.

Killifish species not found in permanent locales basically live in puddles. These killifish are usually called annual fish because they don’t live for more than a year; killifish found in more permanent homes can live up to five years. Longer-living killifish usually lay eggs that float on the surface of the water, while annual killifish tend to bury their eggs in the dirt. The eggs of annual killifish can survive without water - sometimes months depending on the species. I would make a fish out of water joke here, but I’m saving it for later, you’ll see why. The eggs will hatch once rain refills their temporary homes. Some killifish species have this whole lifecycle process down to a science in which they can hatch and develop into fully formed, reproductive adults within the span of about two weeks - that’s faster than any other vertebrate scientifically studied thus far. Of course, that also means they die faster, well, unless they eat poop, then they might live longer.

Reproduction really depends on the species when it comes to killifish. Some do the normal fish thing with males fertilizing the eggs of females; females might lay eggs one at a time or in groups; there’s even one species that almost exclusively self-produces in which individuals fertilize their own eggs. And just as different as their mating habits can be, so, too, are their color patterns. Killifish can range from simple browns to dazzling reds, and they can range in size from under an inch (2.54cm) to over six inches (15.24cm)!

Even though they might come in small sizes, they’re still great snacks for other larger fish as well as birds. They’ll swim in schools to help deter predation, but some killifish are attacked from the inside by parasites who will cause the fish to swim belly up thus exposing their shiny bellies to birds looking for an easy meal. Those who don’t become dinner eat plant material as well as insect larvae, including mosquito larvae. Because of this, it’s thought that the presence of killifish may help reduce mosquito populations in an area

All right, I said I would come back to this. Some killifish species might qualify for the best “fish out of water” award. The mangrove killifish specifically has been observed surviving more than 60 days out of the water while still maintaining completely normal function. This awesome act is accomplished via their ability to breath through their skin. Technically speaking, they can also poop through their skin, but I’m not sure if you guys would count that as less awesome or even more awesome.

For more facts on killifish, check out the links in the description. Give a thumbs up for fish, and thank you for watching Animal Fact Files.