Fish Suit

From Astral Adventurer's Guide, page 22.

Description
Wondrous item, very rare

This bulky suit, which fully encases your head and body, takes 1 minute to don or doff. While worn, it enables you to breathe in an airless environment and renders you immune to the harmful effects of any gas that surrounds you. The suit also grants you a swimming speed equal to your walking speed while underwater, or a flying speed equal to your walking speed in an environment with no gravity.