Basking sharks (Cetorhinus maximus), are the world’s second-largest fish (whale sharks being the first). In summer, it swims open-mouthed at the surface, filtering out plankton. Every hour, the shark passes up to 395,000 gallons (1.5 million liters) of seawater through the huge gills that almost encircle its head.
My oceanography professor told me the gills on huge basking sharks are large enough for small humans to swim in and out of.
(Info from AMNH.)