Fig. 1

Pseudogobio esocinus. (A) Resting state, (B) feeding state, (C) wider mouth, and (D) narrower mouth. In the panels C and D, the bones in the head and mouth parts of the fish specimens are stained by Alizarine Red S to visualize anatomical differences. This fish usually exhibits remarkable upper jaw protrusion by opening its mouth to suck prey from the bottom sand (i.e., bottom sucking). It repeats this process by opening and closing its mouth. A wider mouth is linked with markedly downward protrusion, whereas a narrower mouth is linked with more forward and moderate protrusion. Photos (C) and (D) are reprinted from Endo and Watanabe ([20]; partial modification)