Department of Ecology, Evolution and Organismal Biology, Brown University, Providence, RI 02912, USA.
3D Anatomy Studios, Providence, RI 02860, USA.
J Exp Biol. 2022 Jun 1;225(11). doi: 10.1242/jeb.244294. Epub 2022 Jun 6.
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. Thus, the shape of the axial muscles and skeleton may affect suction feeding mechanics. Royal knifefish (Chitala blanci) have an unusual postcranial morphology, with a ventrally flexed vertebral column and relatively 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 with 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. The large epaxial muscle (25% of body mass) shortened at high velocities to produce large neurocranial elevation and vertebral extension (up to 41 deg, combined), as well as high muscle mass-specific power (up to 800 W kg-1). For the highest power strikes, axial muscles generated 95% of the power, and 64% of the axial muscle mass consisted of the epaxial muscles. The epaxial-dominated suction expansion of royal knifefish supports our hypothesis that postcranial morphology may be a strong predictor of suction feeding biomechanics.
射水鱼通过强有力的口腔扩张将水和食物吸入嘴中。之前对大口黑鲈（Micropterus salmoides）、蓝鳃太阳鱼（Lepomis macrochirus）和斑点叉尾鮰（Ictalurus punctatus）的 XROMM 研究表明，高性能射水的吸力超过 90%来自轴向肌肉。因此，轴向肌肉和骨骼的形状可能会影响射水的力学机制。皇家刀鱼（Chitala blanci）具有不寻常的后躯形态，其脊柱向腹侧弯曲，并且轴上肌肉的质量相对较大。基于它们的体型，我们假设皇家刀鱼会通过利用较大的颅神经提升、脊柱伸展和轴上缩短来产生高功率的射水。正如预测的那样，与迄今为止研究的其他三个物种相比，C. blanci 产生了高吸力扩张力（高达 160 W），这是通过增加体积变化率和口内亚大气压来实现的。较大的轴上肌肉（占体重的 25%）以高速缩短，从而产生较大的颅神经提升和脊柱伸展（最大可达 41 度，两者结合），以及较高的肌肉质量特定功率（高达 800 W/kg-1）。在最高功率的射水中，轴向肌肉产生了 95%的功率，而轴向肌肉的 64%由轴上肌肉组成。皇家刀鱼以轴上肌肉为主导的射水扩张支持了我们的假设，即后躯形态可能是射水生物力学的一个强有力的预测因素。
