Misterjaw (voiced by Arte Johnson) was a blue-colored great white shark (who wore a purple vest with white collar, a black bow tie and black top hat) who liked to leap out of the water and shout "HEEGotcha!" or "Gotcha!" at unsuspecting folks who would run off in terror. He spoke with a German accent and was known to mispronounce words, such as "knucklehead" pronounced as "ka-nucklehead". He also had a sidekick, a green-scaled, brown bowler hatted Brooklyn-accented catfish named Catfish (voiced by Arnold Stang) who usually referred to Misterjaw as "boss" or "chief"; Misterjaw usually called Catfish either "pal-ly", "fella" or "sonny" when in a good mood, or names like "dumbkoff", "ka-nucklehead" or "macaroni brain" when irritated. At times, Misterjaw would mistakenly address his sidekick as "Dogfish", only to correct himself a split second later by saying "I mean, Catfish."
The primary goal of Misterjaw and Catfish was to catch Harry Halibut (voiced by Bob Ogle). In several instances, the duo were pursued by Fearless Freddy the Shark Hunter (voiced by Paul Winchell) in Merry Sharkman, Merry Sharkman and To Catch a Halibut.