Most fishes have external fertilization. In external fertilization, the eggs are fertilized outside the female’s body. The male hovers close to the female and spreads a cloud of sperm cells over the eggs she releases. The young develop outside the female’s body.
A shark’s mouth contains jagged rows of teeth arranged in rows. Most sharks use only the first couple of rows for feeding- the remaining rows are replacements. If a shark loses a front-row tooth, a tooth behind it moves up to replace it.
Sharks spend most of their time hunting for food. They will attack and eat nearly anything that smells like food. Because they see poorly, sometimes they swallow strange objects. One shark was found to have a raincoat, three overcoats, and a license plate in its stomach !
Most species of fish have a 'swim bladder' - an air-filled sac inside their bodies, which makes them float. These fish use their swim bladders to stay at one level. That way, they don't have to use much energy to stay in one place.
They can change level by swimming or by adding or
removing air from the bladder. Other fish, such as