Cartilaginous vs. Bony Fish

What kind of an animal is humuhumu? It’s a fish! What about a shark? They are, in fact, ALL FISHES! But sharks are a special type of fish. The biggest difference between sharks and other fish is their skeleton. A fish has a skeleton of bone while sharks have a skeleton made of CARTILAGE. Cartilage is a flexible yet tough material that provides support for the body.


What are Chondrichthys?

Chondrichthy is the family of sharks and there are actually more than 350 species of sharks. Tiger Sharks and Great White Sharks are two types of sharks found around the Hawaiian Islands and their teeth are specially formulated for their prey type-fish, sea turtles, marine mammals, invertebrates, etc. You can actually tell what kinds of things sharks like to eat by looking at a shark’s teeth. Mako Sharks have large, longer, pointed teeth for grabby slippery prey like fish or octopus but Nurse sharks have small, flat teeth that are used to crush hard shells of crabs and lobsters. Tiger Sharks have large, triangular, serrated teeth that almost look like knives. 

Sharks are able to replace their teeth. Our baby teeth fall out and get replaced by adult teeth, but once you get those, you’re done replacing teeth. Sharks have these rows of teeth that are ready to replace the front teeth. If a tiger shark went to attack its prey, and in the process, lost some teeth, the teeth in the back will then come to the front, like a conveyor belt, to replace the lost teeth. Sharks can replace about 10,000 teeth in a lifetime! Sometimes sharks lose teeth and we find them and make them into a necklace, but the ancient Hawaiians used to use them to make weapons like this one seen here.


Shark Size

Sharks come in all different shapes and sizes. The Dwarf Lantern Shark is the smallest shark, which only grows to be the length of a pencil. The Tiger Shark and the Great White Shark, on the other hand, are both very large fish. However, they are not the largest. This title goes to the Whale Shark. The Whale Shark is as large as a school bus. You may think that a shark that big would have rows and rows of enormous teeth, but they don’t. They’re as gentle as can be and don’t even eat large fish.


Shark Senses

Sharks are sometimes called the ‘perfect hunters’. This is for a good reason; sharks have been around the earth since the time of the dinosaurs and have not changed too much. They are highly adapted to their life and have many different things that help them to survive. Some sharks sense of smell is so strong that it can smell one drop of blood in a large (Olympic sized) pool. They also have a sense organ in a line along their body called the LATERAL LINE (point to it on either a picture or use the bony fish skeleton) that they use to feel movement or vibration in the water. The body and heart releases very weak electricity. Sharks are also able to feel electrical charge through their AMPULLAE OF LORENZINI so they are able to find fish who have hidden themselves below the sand. 



Sharks have something called a nictitating membrane. We have eyelids to help keep our eyes moist. Since sharks live in the water, their eyes are always moist. So they have these “eyelids” to protect their eyes. Right when they are about to attack their prey, they cover their eyes for protection.


How They Breathe

Sharks use their gills to breathe oxygen from the water. Most sharks have 5 gill slits but there are few that 6 or 7 gill slits. The dorsal fin of a shark helps it to keep balance in the water just like a dolphin. The bodies of most sharks are usually a mixture of a light color on the bottom and a darker color on the top. This is a form of camouflage called COUNTER-SHADING. When looking up from under the shark, their light underside will blend in with the bright ocean surface lit by the sunlight. When looking down from above the shark, the dark top side of the shark will blend in with the deep dark ocean bottom. A sharks skin can feel rough. Their skin is actually made up of tiny modified teeth-like scales called DERMAL DENTICLES. This shape helps the shark swim fast and smooth through the water. If you were to pet the shark from head to tail, it would feel smooth. 


Marine Debris

A lot of marine animals, including our sharks, are falling victim to something called “Marine Debris”. This is just a fancy word for trash that is found in the ocean. “Marine Debris" is rubbish left behind by people and it can be very dangerous to animals. It could be left on the beach when people go swimming or fishing. But trash left on the side of the street or even up in the mountains can find its way down into the ocean by catching a ride on the wind or flowing down a river. Trash left anywhere can eventually make its way into the ocean. It is a very big problem but there is a very easy solution. To help, you can pick up rubbish and throw it in the trash can. You can also reduce, reuse, and recycle things and make new products out of what was once trash. If we all can do this, our ocean friends, like our sharks, will be much safer.

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