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Page 193 Yu et al. Intell Robot 2022;2:180-99 https://dx.doi.org/10.20517/ir.2022.10

A proper electronic communication system facilitates the communication of multiple robot fishes. Since the
robot fish’s electronic communication system frequently uses the same channel, collisions always occur
during communication. To solve this problem, based on carrier sense multiple access with collision
[54]
avoidance (CSMA/CA), an electronic communication system was proposed by Zhang et al. . This system
incorporated a communication channel detection circuit and employed a CSMA/CA-based protocol. The
simulation and experimental results validate the system’s effectiveness. Nevertheless, this communication
system suffered from effective bandwidth loss.

[55]
Fish can perceive information from the surrounding fluid using the lateral line system (LLS) . This has
serious implications for their underwater survival. Inspired by the excellent performance of the fish’s LLS,
the artificial lateral line system (ALLS) was designed and applied to the robot fish. Predictably, ALLS plays
an important role in improving the interaction and collaboration capabilities between adjacent robot fishes.
Zheng et al. established ALLS by composing an array of pressure sensors . This ALLS could detect vortex
[56]
streets generated by adjacent robot fish. According to the experimental results, it allowed the robot fish to
perceive the relative vertical distance and yaw/pitch/roll angle with the adjacent robot fish. Furthermore, the
oscillation amplitude/frequency/offset of the adjacent robot fish could also be sensed. However, the study
was limited to the perception of the outside world by only one robot fish applying ALLS. Therefore, Zheng
et al. further investigated ALLS on the perception of longitudinal separation sensing of two robot fishes .
[57]
Longitudinal separation implies that the two robot fishes maintain constant lateral spacing, change the
longitudinal spacing, and keep the robot fish within the influence of the vortex produced by another robot
fish. The meaning of longitudinal spacing and lateral spacing is clearly shown in Figure 12. The authors
experimentally obtained a qualitative relationship between the longitudinal separation of two robot fishes
and the ALLS-measured hydrodynamic pressure variations. The effectiveness of ALLS in relative state
awareness applications was also verified. Unfortunately, the study was limited to qualitative analysis, with
no quantitative analysis.

Using vision for communication is the most straightforward method. Berlinger et al. devised a new method
of communication in schools of robot fishes that was inspired by the fact that fish could use vision to
[58]
coordinate their motions . The vision system of the robot fish was comprised of two cameras and LEDs.
Through the algorithm, the robot fish could quickly determine the location of the adjacent robot fish after
recognizing the light. The experimental results demonstrate that the robot fish could perform a variety of
school behaviors using visual information. However, it is unclear whether the communication technology is
still effective in environments that may hinder vision, such as murky waters.

We find that communication can be established between the robot fish and the fish school. When the robot
fish swims in the water, it attracts the fish school to move closer to it. Eventually, the robot fish becomes the
leader, leading the whole school of fish to swim forward, as shown in Figure 13. It is worth noting that the
robot fish does not have smell, sound, or light to attract the fish. We hypothesize that the tail vortices
created by the robot fish when it swims are the cause of this phenomenon. The swimming performance of
robot fish is much inferior to that of fish. One of the reasons for this is that the tail vortices are not fully
utilized. As is known, creatures have always tended to be profit-oriented. When fish perceive tail vortices,
they tend to take advantage of them. In turn, it follows the robot fish, which eventually leads to this
phenomenon. This brings the robot fish into communication with the fish school. We are confident that
finding out how to exploit this communication would be meaningful research.

5. CHALLENGES AND FUTURE WORKS
Thanks to a lot of research on bionic robot fishes in recent years, significant progress has been made.