Locomotor Biomechanics in Stream Gobies, Rhinogobius sp.: Functional Performance of Waterfall-Climbing Behavior

Gobiidae is the taxonomic classification of a large fish family comprising over 2,000 species. A few goby species have the unique ability of scaling waterfalls using pelvic fins that are fused into a suction disc (pelvic sucker) located on the ventral side of the body, aiding them in upstream migration to freshwater feeding and reproduction locations. This study aimed to investigate the locomotor biomechanics of Rhinogobius goby fish due to the lack of literature in the area, and to better understand solutions this particular gobiid species exhibits while facing physical challenges. In particular, climbing performance variables (pressure differential, force, endurance, and kinematics of attachment), pelvic sucker fatigability, and ontogenetic patterns of physical development and suction adhesion were evaluated. The present study found that in relation to the body mass of the Rhinogobius sp. specimens, total body length (TBL) showed slight allometry, maximum sucker area (MSA) showed moderate negative allometry, and suction force (Fps) showed strong positive allometry. These findings suggest the ability of Rhinogobius sp. to retain climbing capacity with maturity, similarly to Sicyopterus japonicus, another waterfall-climbing goby that occurs in the same locale. While a wide range of variability of sucker fatigue time was observed, no clear ontogenetic pattern of fatigue was found. Additionally, dissections of the Rhinogobius spp. specimens suggested similar skeletal and muscular pelvic structure to S. japonicus, in particular the anatomical structures that control the pelvic sucker organ during climbing adhesion