Killifish biology has long intrigued fish enthusiasts and scientists. But human encroachment, habitat loss and climate change are dwindling killifish populations in the wild. Thankfully, collection efforts by conservationists are saving these creatures. The conservationists distribute specimens and their eggs to academic and hobbyist circles for captive breeding and stewardship.

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To date, at least 1,270 killifish species are known worldwide, according to Portland State University’s Podrabsky Laboratory. Every continent, save Antarctica and Australia, has killifish.

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The BBC and Smithsonian Magazine rank killifish among Earth’s “most extreme” fish. They live in small bodies of water that dry up quickly. Through evolution, they’ve adapted to grow and develop rapidly before their watery homes evaporate. Some killifish species even mature in just a couple weeks.

To illustrate, the arrival of rain spurs the tiny fish embryos, dormant in the sediment, to rapidly develop and hatch. The fry next attain sexual maturity, complete the mating cycle, and deposit new batches of embryos — all before the puddle evaporates, sometimes within 14 days. Other adaptations, described by Science magazine, are that killifish can handle intense pollution, fluctuating salinity and unpredictable pH. Superfast maturation, highly evolved versatility and extreme coping strategies toward harsh water conditions have inspired many scientific studies on killifish to determine their secrets on aging and adaptability.

Moreover, some species’ embryos, reported by Ecology Journal of the Ecological Society of America (ESA), are hardy enough to survive birds’ digestive tracts. In other words, these killifish embryos hatch even after ingestion by waterfowl. Birds can consume these resilient floating embryos from one body of water then deposit them in a different body of water, miles away, therefore ensuring species dispersion to counteract inbreeding risks.

Inhabitat caught up with David Huie and John Pitcairn, avid killifish hobbyists who helped found the San Diego Killifish Group (SDKG), a Southern California satellite of the American Killifish Association (AKA). From 1980 to the early 2000s, both Huie and Pitcairn participated in several conservationist collection teams, traveling to Mexico to save endemic killifish.

On the left, David Huie sitting at a desk speaking to a group. On the right. John Pitcairn smiling at camera

Inhabitat: What anecdotes can you share that show how killifish have become endangered?

Huie: There was a time — the early ‘90s — when a professor and his grad students collected desert killifish to breed in the laboratory but lost them. They returned to collect more in the wild, but the fish were eradicated. Sometime before year 2000, the Mexican government, to grow more corn in the desert, pumped the water down 70 meters, drying up streams. Almost everywhere we collected were signs fish weren’t going to be there much longer. Many have gone extinct.

But some species are just extirpated in the wild. You can’t find them out there anymore. But we have them in the hobby, the Cyprinodon alvarezi, for example. Ceciliae — they were named after the researcher’s daughter — they went extinct before we got there. I think veronicae was extirpated, but might still be in the hobby, and one type of fontinalis is still in the hobby. The hobby’s the only thing keeping them from extinction.

Pitcairn: Actually, there’s still new killifish being found all the time, even during collections. In a way, we stop them from going extinct before they’re discovered [scientifically recognized and named].

Inhabitat: What fascinates you about killifish?

Pitcairn: They’re neat fish because they aren’t common in stores. Lately, I’m getting into nothobranchius. There are fewer and fewer people who have nothos, making them hard to get. So somebody needs to start breeding them to keep them around.

killifish swimming in aquarium

Inhabitat: Killifish can be tough to breed. That can make them rare in pet stores, making them highly prized.

Huie: If you really want a variety of killifish, you just won’t see them unless you’re in the hobby, for no store will carry them by choice, since few customers buy them.

Pitcairn: I went by a local fish store the other day and, surprisingly, they had a half-dozen pair of gardneri. Usually you don’t even see those. Killifish aren’t often in stores, mainly because they’re not easy to mass produce. Something like swordtails, you throw half a dozen pairs in a pond — you can go back and harvest a couple hundred fish.

Huie: Same with cichlids — you spawn a pair, you’ll get a thousand. To get a thousand killifish, you’d have to work at it. You’ll maybe get just 20 to 30 per spawn.

Pitcairn: Depends. With nothos, you can get 50, but then you can also get three, which is frustrating. It’s not so much difficult [to breed killifish] as it is labor-intensive.

Inhabitat: How else are hobbyists protecting killifish species from extinction?

Pitcairn: It’s more important to try and keep the species we’ve got, so hybridizing is frowned upon.

Huie: Before 1960s, European killifish hobbyists crossbred killifish — it wasn’t about making a better-looking killifish — but just to find out which ones were related, by getting viable fry. In fact, a lot of books then were full of hybrids. But in the ‘60s and ‘70s, when they started finding different types of killifish, it became a real problem because you wanted to have the killifish name — hybrids just muddled that. So from the ‘70s to ‘80s, it became anathema to have hybrids.

Inhabitat: What can you share about the hobby’s history in the U.S.?

Huie: The reason the AKA started, and killifish became a hobby, was because at that time it was expensive to get killifish, but relatively economical to send eggs. For peat spawners, you’ve a couple of months where you can send eggs through the mail without a problem. Then for egg-layers, you’ve about a week or two where you can just mail eggs. That’s so much cheaper and easier than sending fish — it’s a smaller package, without worrying about water. Plus, eggs are more temperature-tolerant.

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The first time I really saw killifish as a group was when our friend Monty Lehmann became active as a killifish breeder. He contacted killifish people all over because, generally, there were only a few species available in pet stores back in the ‘70s. Even now, depending on availability, there’s not that many. So in the late ‘70s, I made Monty’s acquaintance, and he tried to get our group going in San Diego. That was a baby brother group to this group [SDKG]. That group kind of dissipated when Monty moved.

Inhabitat: How did the current SDKG group start?

Huie: We had board game meetings on Fridays and Saturdays. While we played Risk, we’d talk about fish. So our original name was San Diego Fish & Game.

Pitcairn: San Diego Killifish and Games — that’s how we got San Diego Killifish Group now, because of the same initials, SDKG.

Huie: Our group realized if we wanted to see killifish we didn’t have, we needed to host a show. To get the fish and egg listings, the group had to be part of the AKA. The AKA still supports the show because they run a Killifish Hobbyist of the Year award, where you receive points for entering fish in different sanctioned shows. It’s great for the hobby and killifish as a whole because you’re sending fish across the U.S.

+ San Diego Killifish Group

Photography by Mariecor Agravante / Inhabitat