It happened in Ranma Movie 2 (the dub at least.)
	When the girls started disappearing, Genma (of course) told 
Ryouga: "Didn't you know that these seas are filled with evil, man-eating 
octopi?" (or words to that effect.)  Ryouga predicatably panics over a 
similar fate happening to Akane, and when the next girl disappears, Genma 
stoically pronounces "Curse those evil octopi."

In the sub, don't they say something like 'The kidnapper is a GHOST!!!'?

Kun-chan...