Planet Earth's largest fish Sharon Spence Lieb Friday, May 4th, 2012 Tweet Back To Story × Photo Being eye to eye with the biggest fish on Planet Earth is scary. But this magnificent encounter is life changing. All you need is a snorkel and courage. × Photo Whale sharks congregate offshore Cancun, Mexico from May-September. They dine on a buffet of fish eggs and plankton. × Photo Whale sharks are light grey, white spotted and often grow to be 40 feet long. Scientists have tracked them living at depths of up to 2,300-feet.