1837, shortened form of cockroach (q.v.), in contemporary writing said to be from a polite desire to avoid the sexual connotation in the first syllable; meaning "butt of a marijuana cigarette" is first recorded 1938, perhaps from resemblance to the insect, but perhaps a different word entirely.
"small freshwater fish," early 14c., from O.Fr. roche (13c.), perhaps from a Germanic source.