‘The ultimate setting’: Why Japan wants to grow fish in space

Scientists at Okayama University of Science hope to make aquaculture part of space-exploration programs

With the world’s population continuing to grow, moves are underway to determine whether human activity could expand beyond our Earthly realm. One example is NASA’s Artemis program, which envisions building a lunar base that could support long-term habitation.

One major challenge in such an endeavor is sustaining astronauts on long space missions and ensuring that enough essential nutrients, such as protein, vitamins and omega-3s, are provided. Against this backdrop, researchers at Japan’s Okayama University of Science are investigating whether fish and other species such as shrimp could be successfully reared in space. By establishing a Closed Recirculating Aquaculture System (C-RAS) that uses a uniquely formulated water called The Third Water, they want to prove the feasibility of aquaculture as a food solution for astronauts.

The work is the brainchild of Associate Professor Toshimasa Yamamoto. By integrating a terrestrial C-RAS model with specialized equipment adapted for space, he hopes that his team can be the first in the world to farm fish where no fish has gone before.

“When it comes to raising organisms in a completely closed environment, outer space is the ultimate setting,” Yamamoto told the Advocate. “As humanity looks to create and sustain life-supporting systems beyond Earth, research like ours becomes essential. Our work had been under consideration for some time before we launched our space aquaculture experiments three years ago.”

The larger goal of Yamamoto and his colleagues is to conduct a full-scale aquaculture experiment aboard the International Space Station (ISS) by around 2030. For now, the team is researching how different species, including plankton, respond to hypergravity (when the force of gravity is greater than normal on Earth) and microgravity (when the force of gravity is less than normal on Earth).

Hatching and feeding experiments with Kuruma prawns (Marsupenaeus japonicus), greasyback shrimp, flounder, red sea bream and tiger pufferfish have produced encouraging results. Plankton can withstand hypergravity and work is underway to determine whether they also respond well to microgravity. Red sea bream eggs have hatched successfully under simulated microgravity and footage of the feeding behavior of Kuruma prawns has been obtained in the same conditions. The team has also gained valuable insights into specific growth rates (SGR).

The Third Water is an artificial breeding water with a pH of seven that has been optimized to include only essential elements such as sodium, potassium and calcium. This allows marine and freshwater fish to be raised together, but the water’s low density has been a challenge for Yamamoto and his team. Outer space, however, is a viable location for the rearing system.

“When fish spawn, the male releases sperm over the eggs to fertilize them,” said Yamamoto. “But the density in our Third Water is so low that all the eggs sink. Even after hatching, the larvae don’t float, and if they can’t swim, they can’t feed on plankton drifting in the water. In a weightless environment, however, the eggs and larvae remain suspended. For us, that changes everything. The biggest challenge we’ve faced – the sinking of eggs in low-density water – is instantly solved in space.”

The C-RAS system is designed to be fully automated and to operate without water exchange for three months, in line with the typical cargo resupply interval to the ISS. It will include a completely closed-loop setup to handle feeding and the monitoring and control of water quality, temperature, dissolved oxygen and salinity. Aquaponics will be another key component to prevent waste, by recycling fish waste as nutrients for plants.

Possible hurdles include power outages or pumps shutting down, but raising living organisms in zero gravity brings other challenges, said Yamamoto. For example, shrimp shells become thinner, while in freshwater fish, the bone density of structures such as the skull decreases. How these species will adapt in space is still largely unknown. By far the most important task for Yamamoto and his colleagues is to continue evaluating how hypergravity and microgravity impact hatching, species behavior and whether larvae feed successfully.

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Yamamoto’s research suggests that red sea bream, flounder, greasyback shrimp and grouper are potentially space-worthy.

“Feed conversion efficiency is one of our top priorities, and with grouper, for example, it only takes about 1.2 kilograms of feed to produce a kilogram of fish,” said Yamamoto. “Nutrition is important, and astronauts can obtain this in tablet form, but relying on that alone for extended periods would take a toll on their mental well-being. We also want to farm popular seafood species. When it comes to essential fatty acids and high-quality protein, fish is the clear choice.”

Research into the potential of aquaculture in space isn’t entirely new. In France, the French National Institute for Ocean Research (Ifremer) has been investigating space-based fish farming as a food solution for future moon and Mars missions. Yamamoto’s project is different in that its scope is more extensive, covering a broader range of species including crustaceans and plankton. Yamamoto says that there is already much to learn from fish when it comes to rearing them in space and hopes that the lessons he has learned so far from his work can make valuable contributions.

“Fish maintain neutral buoyancy through their swim bladders, which essentially means that they are already adapted to living in a state of neutral gravity,” he said. “Even on Earth, they are effectively in a weightless environment, since they regulate buoyancy within water. From birth, they are equipped to float – that’s a critical factor. We also know that bacteria, phytoplankton and zooplankton are not negatively impacted by microgravity, and that bacteria can carry out nitrification and denitrification. We hope that this information can be put to use in other space- and aquaculture-related endeavors.”

The harsh environment in space and potential hurdles mean that Yamamoto and his colleagues still have much work to do. Nevertheless, the prospect of enjoying fresh, nutritious food grown in space remains a compelling goal for future space exploration.