In 1994, NASA flew four Japanese red-bellied newts on STS-65 for nearly 15 days; two adults died, but 32 newt eggs hatched

Space shuttle launches often make headlines because of the rockets, spacewalks, and flight duration. But when Space Shuttle Columbia lifted off in July 1994, one of the quieter experiments on board involved four Japanese red-bellied newts and a specially designed aquatic habitat. The experiment was part of STS-65, the second International Microgravity Laboratory mission, which carried more than 80 experiments examining how materials and living organisms behave in microgravity.

The seven-member crew launched Columbia on July 8, 1994, and returned to Kennedy Space Center on July 23 after 14 days, 17 hours, and 55 minutes in orbit. At the time, it was the longest shuttle flight yet completed. Among the life-science investigations was an experiment involving Japanese red-bellied newts, Cynops pyrrhogaster, designed to examine fertilisation, embryonic development and the formation of gravity-sensing organs in microgravity.

The mission report recorded that at least 32 newt eggs hatched during the flight. Two of the adult newts died, but the remaining experiment continued, allowing researchers to examine embryos that had developed in space and compare them with ground controls.


An aquarium designed for microgravity

The newts were housed in NASA's Aquatic Animal Experiment Unit, or AAEU, developed by Japan's National Space Development Agency. It was more sophisticated than an ordinary aquarium. The facility was designed to support fish and small amphibians in microgravity, with life-support systems that supplied oxygen, removed carbon dioxide and waste, and controlled the water temperature. The unit also allowed astronauts to observe spawning, fertilisation, embryonic development and animal behaviour.

Four experiments used the AAEU during STS-65. One examined how fish adapted their vestibular systems to microgravity. Another investigated the development of otoconia, the tiny mineral structures in the inner ear involved in sensing orientation and gravity. A third examined the fertilisation and embryonic development of Japanese newts, while a fourth investigated mating behaviour and egg development in medaka, also known as Japanese rice fish.

The newt experiment involved adult females and eggs. The females were induced to lay eggs in orbit, allowing researchers to observe early development under microgravity. NASA's later summary of the experiment records that two adult newts did not survive the flight, one dying on flight day five and another on flight day nine.

The deaths created an additional challenge for the crew because a decomposing animal could affect the water system and the other specimens. The mission records show that astronauts ultimately carried out an in-flight maintenance procedure to remove the dead newts and preserve them for examination after the flight. The procedure was completed in the weightless environment rather than simply leaving the animals in their cassettes.

The AAEU also experienced operational problems during the mission, including an issue with water circulation in one cassette. Nevertheless, the experiment continued, and the crew was able to observe the developing embryos. The mission report states that at least 32 newt eggs hatched, while at least 25 medaka fry also hatched during the flight.

What the newt eggs revealed

The significance of the experiment was not that scientists had discovered that life could somehow begin in space. The eggs were part of a controlled biological experiment, with researchers interested in what happened to development when gravity was greatly reduced.

The mission report says the space-developed embryos could be compared with eggs developed under Earth's gravity to study embryonic development in microgravity. Researchers used video observations and postflight analysis to examine the embryos and compare their development with ground controls.

Later NASA records summarising the experiment report that the flight and ground-control groups developed at similar rates based on morphological analysis. Researchers also found differences in the development of gravity-sensing structures in the inner ear. In particular, flight-reared larvae showed changes in the development of the otoconia and associated structures, giving scientists another way to examine how gravity influences the developing vestibular system.

Newts were useful subjects for this kind of research because their eggs and embryos are relatively accessible for observation, while their development provides an opportunity to study gravity-sensitive organs as they form. The Japanese red-bellied newt was therefore well suited to an experiment that had to operate inside a compact aquatic habitat in the Shuttle's Spacelab.

The newts were only one part of a much larger biological programme aboard Columbia. NASA says STS-65 carried more than 80 experiments involving more than 200 scientists from six space agencies. Fifty of those investigations were in the life sciences, covering areas including space biology, human physiology, bioprocessing and radiation biology. The European Space Agency's Biorack facility also carried biological samples including cells, eggs, sea urchin larvae, fruit flies and plant seedlings.

The newt experiment nevertheless offered an unusually tangible look at what microgravity could mean for living organisms. Eggs were fertilised or developed in space, embryos continued to grow, and some eventually hatched. The results did not show that life could originate in orbit, but they demonstrated that important biological processes, including embryonic development, could continue in the microgravity environment.

For researchers thinking about longer human missions, that distinction matters. If people eventually spend months or years away from Earth, understanding how gravity affects reproduction, development, and the formation of gravity-sensing organs could become increasingly important. The small group of newts aboard Columbia did not answer all of those questions, but their brief journey provided another piece of evidence about how life responds when one of Earth's most familiar environmental forces is largely removed.