My Little Flying Fish is Sick(1982)

Overview

An anime about Operation Castle and the demise of the crew on the Daigo Fukuryuu Maru (S.S. Lucky Dragon 5). On March 1st 1954, a hydrogen bomb went off (that ended up being similar sized to the atomic bomb dropped on Hiroshima). The radioactive ash fell on the crew, poisoning them, as well as local marine life--that talk and wear human clothing.