Whale shark is massive but eats ocean's smallest creatures

"What is the biggest fish?" asked Rebecca Lothspeich, 11, a rising sixth-grader who will attend Libertyville's Highland Middle School in the fall.

The biggest fish is a shark - the whale shark. How big is it? The largest is thought to have been 65 feet in length - that's longer than a six-story building is tall.

The plus-sized whale shark weighs about 60 tons - that's heavier than an 18-wheeler. But don't be afraid. These guys have a big appetite for the tiny stuff - plankton, nekton, small fish, squid and crustaceans. They can't gulp anything bigger than a quarter.

Can the gigantic whale shark hide? Its unusual markings, soft gray with spots and stripes and a white belly, is a type of camouflage you might find on a bottom-feeding fish. But these big fish grab their meals at the ocean's surface and the world is their ocean. Whale sharks travel across the warmer ocean waters throughout the planet.

What scientists are trying to piece together is how and what the massive whale shark eats and why it has some of the same characteristics found in bottom-feeder fish. Experts from the Georgia Aquarium, the University of South Florida, Mote Marine Laboratory and Mexico's Project Domino have been studying whale sharks for the past five years.

Whale sharks have a huge, 4-foot wide mouth right at the tip of their snout. They have lots and lots of tiny teeth - 300 rows inside their lips. It's all part of a huge filtering system that is present in two other shark species.

The way they eat is typical for some bottom-feeding fish. They open their huge mouths and gulp in gallons and gallons of ocean water. Mixed in the water is nutrient-rich plankton and nekton. The watery mix rushes over the teethy filters which capture the nutrients and shoot water out through the gills. These giant animals gulp about nine pounds of the tiny plant matter per hour.

The Georgia Aquarium in Atlanta, the only U.S. aquarium that features whale sharks, has been sending researchers to Mexico to study the animal's habits. Scientists were surprised to learn how far these big fish can travel. One tracked by satellite was found cruising from Mexico and voyaging half way to Africa. In August, a field research team will journey to Mexico's Yucatan peninsula to gather more information about these amazing fish.

It's not an understatement to say that the Georgia Aquarium's home for its four whale sharks is humongous - the size of a football field. Visitors can observe whale sharks Taroko, Yushan, Alice and Trixie through a viewing window or a 100-foot-long acrylic tunnel.

These fish may be big eaters, but they're not good for eating. Unregulated fishing in some countries has placed them on the "vulnerable" list.

People tend not to see whale sharks unless they go look for them on tours. The world's biggest fish shy away from beaches, preferring the open sea for their home.

Check these out

Cook Memorial Library in Libertyville suggests these titles on whale sharks:

• "The Whale Shark" by Kris Hirschmann

• "Incredible Fish" by John Townsend

• "Classifying Fish" by Richard and Louise Spilsbury

• "Surprising Sharks" by Nicola Davies