Fig. 1. Schematic picture of a zebrafish larva, at approximately 5 d.p.f. The eye, intestine and swimbladder are marked on the drawing. The intestine is divided into proximal intestine (PI; also referred to as the intestinal bulb), middle intestine (MI) and distal intestine (DI). The length of the larva is approximately 3.5–4 mm. The arrows indicate the starting point and direction of anterograde and retrograde contraction waves, respectively.