A lot of mischance can happen to tetrapods, but non-tetrdapod vertebrates are also not immune towards misadventures. One example for this is this common barbel (Barbus barbus) from the exhibition of the Deutsches Jagd-und Fichereimuseum (German Hunting and Fishing Museum) at Munich, which was found with its mouth muzzled with a rubber ring:
Common barbel with mouth caught in rubber ring.