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What Is a Cartilaginous Fish?

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Whale Shark / Darcy McCarty, Flickr

Whale Shark (Rhincodon typus)

Courtesy Darcy McCarty, Flickr
Question: What Is a Cartilaginous Fish?
Have you heard the term cartilaginous fish? Here you can learn what that term means, and what types of fish are cartilaginous fish.
Answer:

Cartilaginous fish are fish that have a skeleton made of cartilage, rather than bone. All sharks, skates, and rays (e.g., the southern stingray) are cartilaginous fish. These fish all fall into the group of fish called the elasmobranchs.

Characteristics of Cartilaginous Fish:

In addition to the difference in their skeletons, cartilaginous fish have gills that open to the ocean through slits, rather than the bony covering that is present in bony fish. Different shark species may have different numbers of gill slits.

Cartilaginous fish may also breathe through spiracles, rather than gills. Spiracles are found on top of the heads of all rays and skates, and some sharks. These openings allow the fish to rest on the ocean bottom and draw oxygenated water in through the top of their head, allowing them to breathe without breathing in sand.

A cartilaginous fish's skin is covered in placoid scales, or dermal denticles, tooth-like scales different from the flat scales (called ganoid, ctenoid or cycloid) found on bony fish.

Classification of Cartilaginous Fish:

Evolution of Cartilaginous Fish:

Where did cartilaginous fish come from, and when?

According to fossil evidence (primarily based on shark teeth, which get preserved much more readily than any other part of a shark), the earliest sharks evolved about 400 million years ago. 'Modern' sharks arrived starting around 35 million years ago, and megalodon, white sharks and hammerheads came about 23 million years ago. Read More About Shark Evolution

Rays and skates have been around longer than us, but their fossil record dates back to about 150 million years ago, so they evolved well after the first sharks.

Where Do Cartilaginous Fish Live?

Cartilaginous fish live all around the world, in all kinds of water - from rays that inhabit shallow, sandy bottoms to sharks that live out in the deep, open ocean.

What Do Cartilaginous Fish Eat?

A cartilaginous fish's diet varies by species. Sharks are important apex predators and may eat fish and marine mammals such as seals and whales. Rays and skates, who primarily live on the ocean bottom, will eat other bottom-dwelling creatures, including marine invertebrates such as crabs, clams, oysters, and shrimp. Some huge cartilaginous fish, such as whale sharks, basking sharks and manta rays, feed on tiny plankton.

How Do Cartilaginous Fish Reproduce?

All cartilaginous fish reproduce using internal fertilization. The male uses "claspers" to grasp the female, and then he releases sperm to fertilize the female's oocytes. After that, reproduction can differ among sharks, skates and rays. Sharks may lay eggs or give birth to live young, rays give birth to live young, and skates lay eggs that are deposited inside an egg case.

In sharks and rays, the young may be nourished by a placenta, yolk sac, unfertilized egg capsules, or even by feeding on other young. Young skates are nourished by a yolk in the egg case. When cartilaginous fish are born, they look like miniature reproductions of adults.

How Long Do Cartilaginous Fish Live?

Some cartilaginous fish may live for up to 50-100 years.

Examples of Cartilaginous Fish:

References:

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