Meeting Abstract
Agonid poachers are benthic, heavily armored fishes with modified, robust scales that protect against predation. Although the entire body is covered in a fused armor, scales transition from a flattened scale morphology on the ventral surface to a convex scale on the dorsal surface. We hypothesized the dome-shaped dorsal scales of the Smooth-eye poacher, Xeneretmus leiops, are mechanically reinforced when compared to the lateral and ventral scales. Smooth-eye poachers (n=28) were separated into intact fish (scales left on) and fish with scales removed (skin exposed). Puncture tests were performed on 1) intact fish, 2) partially descaled fish, and 3) scales that were removed from the fish. We measured the fracture point (strength), Young’s modulus (stiffness), and work of fracture (toughness) for each group. Treatments were analyzed using ANOVA with post-hoc Tukey tests. Removed scales were 29% stronger than scales on intact fish and 779% stronger than skin. Removed scales were 27% and 524% stiffer than intact fish and skin, respectively, and 26% tougher than skin. Scales also differed in strength, stiffness, and toughness among the dorsal, lateral, and ventral surfaces of the fish. Dorsal scales were almost twice as strong (9.1MPa ±5.6) as lateral (4.8MPa ±3.9; p=0.005) scales and 1.5 times as strong as ventral scales (5.7MPa±6.9; p=0.019). Dorsal scales were almost twice as stiff (10.4MPa ±8.8) as lateral (5.9MPa ±4.9; p=0.011) and ventral scales (5.3MPa ±3.8; p=0.0009). We predict that the majority of predation attempts are focused along the dorsal surface of this benthic dwelling fish, and therefore, the dome-shaped scales help to increase the resistance to meridional stresses (tooth puncture forces).
