SPRING EEL. A fish of the small order Opisthomi and family Mastacembelidæ, several species of which occur in the fresh waters of the East Indies; they are eel-like in form, with the dorsal fin very long, and the fore part of it composed of low free spines. Allied to this is a small, curious eel (Derichthys serpentinus) dredged from the depths of the North Pacific. See Plate of Eels.