| Summary: | Many swimming fishes in nature have been endowed with high hydrodynamic efficiency and performance, such as low resistance, high speed, and good maneuverability, both when swimming individually and in groups, i.e., using schooling arrangements. The main purpose of the present thesis is to study the fish hydrodynamics through both experimental and numerical investigations, to better understand the physical mechanisms behind high propulsive skills of fish-like bodies, and to build knowledge relevant for the design of greener and more efficient bio-inspired underwater vehicles, which could lead to positive consequences for the environment and the society. Observational experiments were carried out in swim tunnels under different conditions and examined two fish species using different swimming modes, i.e., a labriform swimmer (shiner perch, Cymatogaster aggregate) belonging to median and/or paired fin (MPF) propulsion category, and a sub-carangiform swimmer (Atlantic salmon, Salmo salar) belonging to the body and/or caudal fin (BCF) propulsion category. In the experimental investigations performed on the shiner perch, the examined fish were randomly assigned to one of the three experimental scenarios: a solitary fish (Single), a schooling pair of fish (Pair), and a false pair where a single fish swam alongside a video of a conspecific fish (False pair). The swimming behaviours and metabolisms of the fish were analyzed and discussed among different arrangements. The comparisons suggested that schooling confers both hydrodynamic and behavioral advantages over swimming alone for a gregarious fish, but that the relative contribution of the two mechanisms depends on the speed of swimming. In the experiments carried out on Atlantic salmon, the observed results showed that the examined hatchery-reared fish had lower critical swimming speed than biological data of wild fish and fish swimming in larger flumes. The influence of fish body size and swim tunnel boundary walls on the salmon behaviors in the flume was discussed ...
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