Just off the tip of Mexico’s Yucatan Peninsula is a small island relatively untouched by tourism. Isla Holbox might go unnoticed entirely, except for some high-profile visitors that frequent its warm ocean waters each summer. At an average 40 feet long and 15 tons, the presence of these stately filter feeders is hard to ignore. These are gentle whale sharks—not whales at all, despite their size, but actually the world’s largest fish. Docile and unafraid, they allow us to swim close enough to observe the checkerboard pattern of pale white dots and stripes covering their thick gray skin. If you're looking for a fish tale to trump all others, this is it!