Royal knifefish generate powerful suction feeding through large neurocranial elevation and high muscle power output

Suction feeding in ray-finned fishes involves powerful buccal cavity expansion to accelerate water and food into the mouth. Previous XROMM studies in largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus), and channel catfish (Ictalurus punctatus) have shown that more than 90% of suction power in high performance strikes comes from the axial musculature, with cranial muscles primarily acting to transmit power and control cranial kinematics. Royal knifefish (Chitala blanci) have an unusual hump-like appearance, a product of a curved vertebral column and a large mass of epaxial muscle. Based on their body shape, we hypothesized that royal knifefish would generate high power strikes by utilizing large neurocranial elevation, vertebral column extension, and epaxial shortening. As predicted, C. blanci generated high suction expansion power compared to the other three species studied to date (up to 160 W), which was achieved by increasing both the rate of volume change and the intraoral subambient pressure. Such increases are likely a product of its large epaxial muscle (25% of body mass) shortening at high velocities to produce large neurocranial elevation (18-28 deg) and vertebral flexion, as well as high muscle mass-specific power (up to 800 W kg-1). For the highest power strikes, axial muscles generated 99% of the power, and 60% of the axial muscle mass consisted of the epaxial muscles. This supports our hypothesis that postcranial morphology may be a strong predictor of suction feeding biomechanics. ### Competing Interest Statement The authors have declared no competing interest.