The world's largest mammal, the blue whale, weighs 50 tons at birth. Fully grown, it weighs as much as 150 tons.

One way to tell the age of a fish is by looking at its scales. They have growth rings just like trees. These are called circuli. Clusters of them are called annuli. Each annuli show one year.

Fish swimming at depths of 15,000 feet (almost 3 miles down!) can withstand a pressure of 7,000 pounds per square inch. They are able to live in these crushing depths by pumping gas into their swim bladder.

Fish have gel-slime on their bodies that protects them from parasites.

At 188 decibels, the whistle of the blue whale is the loudest sound produced by any animal.

A newly hatched fish is called a "fry."

The world's largest rodent is the Capybara. An Amazon water hog that looks like a guinea pig, it can weigh more than 100 pounds.

The smallest fish in the world are the pygmy goby and the Luzon goby, from the Philippines, which are only one-half-inch long when they are full grown.

Minnows have teeth located on a bone in their throat.

When an octopus gets angry, it shoots a stream of black "ink".