Investigating the effect of morphology on the terrestrial gaits of amphibious fish using a reconfigurable robot

• Published in: Bioinspiration & biomimetics Vol. 20; no. 4; pp. 46002 - 46017
• Main Authors: Gevers, Louis, Gupta, Astha, Paez, Laura, Fu, Qiyuan, Standen, Emily, Ijspeert, Auke
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 31.07.2025
• Subjects: amphibious fish; Animals; biomimetic robotics; Biomimetics - instrumentation; central pattern generators (CPG); Computer Simulation; Equipment Design; Equipment Failure Analysis; Extremities - physiology; Fishes - anatomy & histology; Fishes - physiology; Gait - physiology; locomotion; Locomotion - physiology; Models, Biological; morphologies; multi-objective optimization; Robotics - instrumentation; multi-objective optimization; central pattern generators (CPG); biomimetic robotics; morphologies; locomotion; amphibious fish
• ISSN: 1748-3182; 1748-3190; 1748-3190
• DOI: 10.1088/1748-3190/addc27

The relationship between morphology and locomotion performance in amphibious fish remains poorly understood, particularly in axial-appendage-based and appendage-based movements. To address this, we introduce Polymander, a reconfigurable robot capable of mimicking Polypterus -like walking and mudskipper-like crutching, enabling systematic investigation of body length and limb movement. Using a CPG-driven controller, we optimize locomotion patterns via multi-objective optimization in simulation, comparing resulting Pareto fronts across different morphological configurations. Our results reveal that (1) mudskipper-like crutching is better suited for short bodies, while Polypterus -like walking is better suited for longer bodies; (2) symmetric anterior-to-posterior motion of the limbs is optimal for crutching, while increased anterior limb movement benefits Polypterus -like walking; and (3) sufficient limb strength is necessary for crutching but less so for walking, where axial bending mitigate its effects. Overall, our findings provide a potential explanation of why Polypterus and mudskippers adopt their distinct gaits, emerging as optimal solutions for their morphology within the broader space of all possible gaits.