Swimming ability is critical for navigating complex benthic habitats, yet the biomechanical strategies demersal sharks employ to modulate body and fin movements across varying speeds remain largely unexplored. This study examines speed-dependent kinematic patterns in the small-spotted catshark (Scyliorhinus canicula), a benthic species with limited endurance for sustained swimming. Using high-speed videography in a flow tank, we quantified adjustments in tail beat frequency, body angle, wave speed and curvature across a range of speeds (0.5–6 body lengths per second). Our results reveal that S. canicula exhibits distinct kinematic shifts as speed increases, adopting a more streamlined posture and increasing tail beat frequency to accommodate higher flow rates. Principal component analysis identified swimming speed as the primary factor influencing kinematic variation, with higher speeds necessitating more consistent body alignment and tail movement. Strouhal numbers within the optimal range for propulsive efficiency (0.2–0.4) at intermediate speeds (1–2 BL s⁻¹) suggest that S. canicula maximizes energetic efficiency within this range, although further research is required to elucidate the metabolic implications. This study establishes a foundational framework for understanding the biomechanics of steady swimming in a demersal shark, providing insights into the ecological and evolutionary pressures shaping locomotor adaptations in benthic species.

Shoaling behavior is known to increase survival rates during attacks from predators, minimize foraging time, favor mating, and potentially increase locomotor efficiency. The onset of shoaling typically occurs during the larval phase, but it is unclear how it may improve across ontogenetic stages in forage fishes. Warming is known to increase metabolic rates during locomotion in solitary fish, and shoaling species may adjust their collective behavior to offset the elevated costs of swimming at higher temperatures. In this study, we quantified the effects of warming on shoaling performance across the ontogeny of a small forage fish, zebrafish (Danio rerio) at different speeds. Shoals of larval, juvenile, and adult zebrafish were acclimated at two temperatures (28°C and 32°C), and metabolic rates were quantified prior to and following nonexhaustive exercise at high speed. Shoals of five individuals were filmed in a flow tank to analyze the kinematics of collective movement. We found that zebrafish improve shoaling swimming performance from larvae to juveniles to adults. In particular, shoals become more cohesive, and both tail beat frequency (TBF) and head-to-tail amplitude decrease with ontogeny. Early life stages have higher thermal sensitivity in metabolic rates and TBF especially at high speeds, when compared to adults. Our study shows that shoaling behavior and thermal sensitivity improve as zebrafish shift from larval to juvenile to adult stages.