Cartilaginous vs. Bony fish
What kind of an animal is humuhumu? It’s a fish! What about a shark? Or a ray? They are, in fact, ALL FISHES! But sharks and rays are a special type of fish. The biggest difference between the sharks and rays and fish is their skeleton. A fish has a skeleton of bone while sharks and rays have a skeleton made of CARTILAGE. Cartilage is a flexible yet tough material that provides support for the body.
Chondrichthys’ (sharks and rays) teeth
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. They eat larger animals, and they use their sharp, knife-like teeth to cut and tear their food. Stingrays also have flattened teeth to crush hard things like crabs.
Sharks and rays 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.
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. They are filter feeders, which means that they swim through the water with their mouth wide open and eat the small animals that get stuck on its gill plates when it filters out water.
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.
They have nostrils which they use to smell in the water. And they have a mouth with lots of teeth. Shark eats fish, squid, crabs, etc. There are many different types of sharks in the world, and they eat different things in the ocean including other sharks. Because of this, the jaws of our sharks are very different in size as well as the shape of their teeth.
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. But if you went the opposite way, it would feel very rough. Some sharks have different tail shapes, but most of them have a similar forked shape with the top being larger or longer than the bottom.
Some rays flap their fins like wings while others move their fins in a wave like a Hawaiian Brown Stingray. Stingray’s have a spine on their tail which is how they got their name. A stingray uses its spine not for hunting but for protection. Most stingrays spend their lives along the ocean floor and are also very well hidden in the sand/rocks. When something comes near it and threatens it, they may whip their tail to scare it away.
If you look at the underside of the stingray, you will see that their gills are there. Many times you will see stingrays lying motionless on the sea floor so in order to breathe, they have an opening called a SPIRACLE behind their eyes which allows water to flow down over their gills. This is a really cool adaptation they have to help them live on the ocean floor.
A lot of marine animals, including our sharks and rays, 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 and rays, will be much safer.