定義： Body/caudal fin propulsion, retaining eel-like body movements and exploiting interactions between the sidewash from an anterior median fin with the next posterior fin, increasing its effective angle of attack
定義： length from the tip of the snout to the tip of the longer lobe of the caudal fin, usually measured with the lobes compressed along the midline. It is a straight-line measure, not measured over the curve of the body
