Inspired by the hierarchical skin architecture of tuna, which features an imbricated scale array working in concert with a dynamic mucus layer to minimize flow resistance, this work systematically develops bioinspired drag reduction surfaces by constructing three-dimensional tuna-scale topographies and subsequently integrating them with advanced functional coatings. Stereolithography 3D printing is employed to fabricate biomimetic scale arrays with gradient inclination angles of 10°, 15°, 20°, and 30°, followed by spray deposition of a superhydrophobic composite coating composed of ZIF-8 nanoparticles and PFOTS, with comprehensive characterization confirming that the inclination angle critically governs surface topography and coating deposition behavior. Drag reduction performance is evaluated using a custom-built elongated channel test, wherein the transit time of water droplets through the channel is recorded to calculate the reduction rate. Experimental results demonstrate that the surface with 30° inclination achieves a water contact angle of 152.9° and an outstanding drag reduction rate of 92.1%, significantly surpassing the performance of individual structural or coating strategies. While the 30° configuration exhibits the highest drag reduction efficiency, the 20° inclination angle is selected as the optimal design for further functional innovation, as it combines exceptional drag reduction performance with superior overall properties including mechanical durability, chemical stability, and anti-icing capability, thereby offering the most balanced and practical solution. Building upon this optimized structure, a liquid-like biomimetic surface is developed by covalently grafting flexible siloxane molecular brushes onto the 20° fish-scale substrate to emulate the lubricating function of the natural mucus layer, yielding a surface that exhibits a water contact angle of 134.2°, an ultralow sliding angle below 10°, and a drag reduction rate of 36.1% under turbulent flow conditions, as measured on a water circulation test platform where pressure drop across the sample surface is monitored to quantify the reduction efficiency. Both surfaces demonstrate outstanding mechanical robustness against sandpaper abrasion, tape peeling, and water erosion, excellent chemical stability across extreme pH conditions and various liquid media, efficient self-cleaning capability, and significant anti-icing performance, as evidenced by substantially prolonged freezing delay times. Computational fluid dynamics simulations consistently reveal that the remarkable drag reduction originates from a shared multiscale synergistic mechanism wherein the fish-scale imbricated macrostructure generates stabilizing counter-rotating vortices that regulate near-wall flow and suppress turbulent bursts, while the functional coatings—whether superhydrophobic ZIF-8 micro-nano roughness or flexible molecular brushes—induce effective interfacial slip that significantly reduces velocity gradients and wall shear stress. This integrated investigation demonstrates that the thoughtful combination of bioinspired structural optimization with tailored surface chemistry offers a durable, versatile, and promising strategy for achieving substantial drag reduction and advancing the practical application of biomimetic surfaces in underwater engineering and marine environments.

Bio-inspired surface; Drag reduction; Tuna skin; Liquid-like coating; Superhydrophobic coating; ZIF-8; Interfacial slip; Surface engineering