Nearly a decade before Sally Ride became the first American woman in space, two humble little mummichogs became the first fish in space. In 1973, these little fish rocketed to space aboard one of the famed Apollo crew capsules as part of Skylab 3, a three-month mission to NASA’s early space station. For three weeks, the fish tumbled about in their plastic bag aquarium, totally disoriented by the lack of Earth’s familiar gravity, until they finally regained their bearings and could once again swim straight.
Those two mummichogs (plus another 48 that hatched from eggs onboard Skylab 3) were the first entries into a long history of orbiting fish who have taught us a great deal about how microgravity affects living creatures. Nearly 50 years later, four zebrafish are now swimming aboard China’s Tiangong Space Station, adapting to their strange outer space environment—except now instead of a simple plastic bag, they’re living in a first-of-its-kind self-sustaining ecosystem.
Four zebrafish swim inside a tank aboard China’s Tiangong Space Station. Credit: CNSA
Last week, China’s astronauts (also known as taikonauts) reported that the zebrafish, launched on April 25th along with some algae, are alive and well. This experiment aims to see how microgravity will affect the fish’s life cycle and other natural cycles within their closed environment.
Microgravity’s effects reach far beyond the weightlessness humans experience in space. It leads to changes in nearly all of our bodily functions, from our bones to our hearts and our brains. In order to spend more time in space, such as on long missions to Mars, it’s absolutely crucial that we understand these biological changes. Humans are complicated and hard to study, though, especially if you want to track changes from birth. That’s where fish come in.
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Zebrafish are a great example of a model organism, a species that’s been extensively studied to help us understand a particular aspect of biology, often in ways we can’t experiment on humans. Although zebrafish might seem quite unlike us, they actually “have many of the same major organs and their bodies generally work the way ours do even down to the cellular level in many cases,” explains University of Washington developmental biologist Aaron van Loon.
Zebrafish are also small, easy to take care of, and actually entirely see-through before they hatch, making it possible for scientists to peer inside them during their development. It’s also a lot easier for scientists to manipulate genetics in these fish, enabling “a lot of important experiments that simply wouldn’t be possible or ethical to perform with humans,” adds van Loon.
Here on Earth, zebrafish have already been used for numerous medical experiments that eventually help humans, “from the inner workings of embryonic development, to the function of immune cells during infection, and even insights into genetic disease,” says van Loon. And in space, they’ve been studied as early as the 1970s, when they flew aboard the Russian Salyut 5 space station mission. More recently in 2015, zebrafish aboard the International Space Station were used to investigate how muscles atrophy in microgravity.
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Many other fish—including those very first mummichogs—have flown to space as well.
For example, the slightly larger (and admittedly, uglier) oyster toadfish soared on NASA’s Space Shuttle Columbia in the late 1990s, so that scientists could watch their brains readjust to Earth’s gravity upon their return. In fact, a whole menagerie of creatures was aboard that flight on Columbia’s STS-90, including “68,000 freshwater swordtail fish, 5,000 freshwater snails, 2,000 goldfish, 1,000 crickets and 125 saltwater toadfish” according to a NASA annual report. On the International Space Station in the 2010s, a school of medaka fish were used to track bone density loss and see how the higher radiation in space degrades their DNA.
NASA archives also contain “several records about the research done using jellyfish, goldfish, guppies, salamanders, and newts,” says NASA archivist Julie Pramis, such as those aboard space shuttle mission STS-65 in 1994 to investigate the critters’ balance, spatial awareness, and mating behaviors.
Similarly to human astronauts, fish are carefully chosen to go to space, and always with a particular mission in mind. From mummichogs to zebrafish and beyond, our little aquatic friends are leading the way for us to brave the final frontier safely, with full knowledge of how to keep ourselves safe and healthy in microgravity.