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weaknesses, using only one method may provide unconvincing results. The combined use of multiple
research methods not only achieves the complementary benefits of each method but also allows each
method to verify the others to ensure the accuracy of the results.

● There is a lack of sufficient research on motion coordination and communication of multiple robot fishes.
Multiple robot fishes in an appropriate formation have been shown to reduce energy consumption [47-53] . In
nature, the number of fish in a school is usually greater than three, and the school is in a three-dimensional
formation. However, the current study has limitations in terms of the number and formation of robot
fishes. Specifically, the number of robot fishes is generally two, and the formation of robot fishes is mostly
flat. The research of three or more robot fishes and the research of three-dimensional formation of robot
fishes will be future research trends. The communication of multiple robot fishes is an intriguing research
topic. Robot fishes need to communicate with each other to form formations, thus reducing energy
consumption. The research on communication among multiple robot fishes has only recently received
adequate attention. The related technology is not yet fully mature and should be tested in the actual
environment. In addition, the research on communication between robot fish and fish schools is interesting
content. We can imagine a future where schools of robot fishes swim together with schools of fish to form a
larger school, achieving energy savings as well as harmony between robot fishes and fish.

6. CONCLUSION
This paper provides a comprehensive review of recent advances in several important fields of bionic robot
fishes. The latest achievements in the development of robot fishes are presented. Based on the discussion of
the main swimming theories of fish, the latest progress in the study of the swimming mechanism is
summarized. The current state of research in the new field of motion coordination and communication of
multiple robot fishes is analyzed.

Based on the survey, the data show that robot fishes in BCF propulsion mode can obtain high propulsion
speed. This reflects the speed advantage of BCF propulsion mode. Robot fishes in MPF propulsion mode
realize a small radius or even in situ turning. The turning radius is an important indicator of
maneuverability. This reflects the high maneuverability of the MPF propulsion mode. The maneuverability
of robot fishes in BCF-MPF propulsion mode is improved compared to robot fishes in BCF propulsion
mode. However, in terms of swimming speed, compared with robot fishes in MPF propulsion mode, they
fail to demonstrate the expected superiority. As a result, robot fishes in this propulsion mode have more
room for advancement. The high-frequency oscillation of the caudal fin can significantly increase the
propulsive speed. The soft robot fish has a low speed of propulsion compared with the rigid-soft coupled
robot fish.

This paper primarily summarizes research results on robot fishes from the last five years, and the reader
should be aware of the paper’s time constraints. In the future, we will make efforts to improve the
swimming performance of robot fishes and continue to track new advances in the research of robot fishes.

DECLARATIONS
Authors’ contributions
Made substantial contributions to the research and investigation process, reviewed and summarized the
literature, wrote and edited the original draft: Li K, Ji Y
Performed oversight and leadership responsibility for the research activity planning and execution, as well
as developed ideas and evolution of overarching research aims: Yu Z