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Synopsis Structures specialized for adherence, such as suction cups, toe pads, barbs, and hooks, are abundant in nature. Many of these structures function well passively and are reversible, making them potent inspiration for biomimetic technology. However, the biological aspect of how these structures are used by animals in nature is often ignored or abstracted, even though active input by the animal often improves the structure’s adhesive performance. The northern clingfish, Gobiesox maeandricus, is a common animal model for bio-inspired suction cups because it performs well where standard cups cannot, such as dry, rough, and fouled surfaces. Here, we investigated whether suction performance is actively modulated in response to increasing flow speeds using a dynamic experimental design. We compared maximum suction pressures, maximum suction forces, and detachment speeds between live and euthanized clingfish. We found that both living and euthanized individuals increase suction in response to faster flows, but that live animals increased their suction to a greater extent, suggesting both behavioral and morphological components contribute to suction performance. Our results indicate that active modulation improves aspects of suction performance, making them important to consider for advancing bio-inspired design applications. 

Synopsis Armor is a multipurpose set of structures that has evolved independently at least 30 times in fishes. In addition to providing protection, armor can manipulate flow, increase camouflage, and be sexually dimorphic. There are potential tradeoffs in armor function: increased impact resistance may come at the cost of maneuvering ability; and ornate armor may offer visual or protective advantages, but could incur excess drag. Pacific spiny lumpsuckers (Eumicrotremus orbis) are covered in rows of odontic, cone-shaped armor whorls, protecting the fish from wave driven impacts and the threat of predation. We are interested in measuring the effects of lumpsucker armor on the hydrodynamic forces on the fish. Bigger lumpsuckers have larger and more complex armor, which may incur a greater hydrodynamic cost. In addition to their protective armor, lumpsuckers have evolved a ventral adhesive disc, allowing them to remain stationary in their environment. We hypothesize a tradeoff between the armor and adhesion: little fish prioritize suction, while big fish prioritize protection. Using micro-CT, we compared armor volume to disc area over lumpsucker development and built 3D models to measure changes in drag over ontogeny. We found that drag and drag coefficients decrease with greater armor coverage and vary consistently with orientation. Adhesive disc area is isometric but safety factor increases with size, allowing larger fish to remain attached in higher flows than smaller fish.