ONE PIECE Episode 39: Luffy Submerged! Zoro vs. Hatchan the Octopus!
Episode 39 of 1180 of ONE PIECE, aired August 30, 2000, 25 minutes. Available with English subtitles and dub where released.
Episode summary
The Straw Hats and Arlong's fishmen are locked in a swashbuckling slugfest, but things take a bad turn when Luffy gets trapped beneath the waves.