Breakthrough in enclosed aquatic ecosystems in space: Supporting zebrafish survival for 43 days

In June 2024, the China space station's closed aquatic ecosystem (CSS's CAES) achieved a remarkable feat: zebrafish completed their life stages, from growth to development and reproduction, in 43 days, setting a new record for space ecological experiments. This milestone not only means progress in China’s space ecosystem technology but also provides valuable data and technical support for closed-loop ecosystems in space missions. The impressive accomplishment is essentially attributed to the innovative design of the CAES, representing an advanced scientific experimental platform that comprises a biological regenerative life support system, a gas balance control system, and a microbial treatment system. This design achieves highly integrated and automated regulation, ensuring the survival of zebrafish in various life stages.

Zebrafish, as a vertebrate model organism with more than 70% genetic similarity to humans, play a vital role in research in life sciences, health sciences, and biomedicine.1,2 The CAES system intelligently integrates life sciences with engineering technology to craft an environment suitable for the long-term survival of zebrafish. On the CSS, these zebrafish are more than just research subjects; they are essential components of the CAES. Zebrafish (Danio rerio), aquatic plants (Ceratophyllum demersum), and microbes form a harmonious micro-ecosystem, where the aquatic plants absorb carbon dioxide and produce oxygen through photosynthesis, playing a pivotal role in the CAES gas cycle.3 Zebrafish receive oxygen and produce carbon dioxide through their metabolic processes. Microbes on the surface and intestines of zebrafish also play a significant role in the decomposition of waste materials and water purification (Figure 1). Thanks to the integration and automation of the control system, the volume of the CAES cultivation chamber has been further improved. Meanwhile, the design of CAES cultivation chambers takes into account the balance of biomass and space, with the animal cultivation chamber set at 750 mL and the plant cultivation chamber at 500 mL. The total volume of the cultivation chamber is 20.8 times the size of the CAES on the Shenzhou-8 spacecraft, which enables the support of more biomass and a richer ecological community.4 The zebrafish and aquatic plants are separated by a perforated partition, with holes providing a vital pathway for the circulation of oxygen and carbon dioxide. Based on a closed ecosystem, the CAES methodically incorporates a sensor network and intelligent algorithms to fully automate lighting time, temperature control, waste filtration, and feeding modules, successfully establishing a self-recycling environment for the long-term zebrafish survival.