What is a Cartilaginous Fish?
Cartilaginous Fish are fish without bones. Instead of bones, they have softer stuff called cartilage. Our skeletons are made of bone, but we also have some cartilage in our bodies. For example, if you hold your nose and wobble it, you’ll see the middle bit is a bit hard, but not as hard as bone. That’s cartilage!
So, if you’re having trouble spelling Cartilaginous, just remember it comes from the work Cartilage. That’s why it’s not Cartiligenous, or Cartileginous, or Cartilogunous or anything else!
The most common types of cartilaginous fish are sharks and rays. like most other fish, Cartilaginous fish mostly
- Have gills, and breathe water,
- Are “cold-blooded” – their body temperature will be the same as the surrounding water, and
- Cannot survive in air.
The things make cartilaginous fish different from other fish are
- They have cartilage, instead of bone. This means that cartilaginous fish don’t make good fossils. For example, the only fossils we have of the Megalodon are of its teeth!
- As fish go, cartilaginous fish have big brains, compared with their body size. There are a few exceptions, but that’s the general rule.
- Most vertebrates make their red blood cells in their bone marrow. Cartilaginous fish don’t have bones, so they don’t have marrow. They use different organs for making red blood cells,
What kinds of cartilaginous fish are there?
The scientific name for the class of Cartilaginous fish is Chondrichthyes, which just means “Cartilaginous Fish”. No surprises there, hey? This class is broken into three main groups, which are in turn divided into 12 smaller groups, called “orders”. These are
- The Chimaeras are the only type of Holocephali that are still alive. They are sometimes called ratfish or elephant fish. They live at the bottom of the sea, and defend themselves with a poisonous spine.
- The Batoids are the rays and skates. There are three groups (called ‘orders’) of Batoids.
- The Rajiformes are the “normal” rays and skates. They have flat bodies, and kind of “fly” through the water.
- The Pristiformes are the “sawfish”. The Greek word Pristis means Saw. Sawfish have a big snout, which helps them sense where their prey is hiding. They should not be confused with Swordfish, which are not cartilaginous fish at all, or the Sawsharks mentioned below!
- The Torpediniformes are the electric rays. Like the electric eels, they generate electricity to stun or kill their prey. Some species can generate enough current to stun a human!
- The Selachimorphs are better known as… Sharks ! The shark’s body is shaped just right for it to flow through the water. Its special skin helps, and also defends it against parasites. Sharks have replaceable teeth! There are 8 different groups (orders) of sharks.
- The Hexanchiformes have six or seven gill slits on each side. Most sharks have only five.
- The Squaliformes have an extra fin on top, and cutting teeth at the top and the bottom.
- The Pristiophoriformes are the Sawsharks – not to be confused with the Sawfish mentioned above! Sawsharks use their toothed snout to hack and slash at the fish they are eating. All species of sawsharks are in danger of extinction.
- The Squatiniformes look like rays. However, their gills are on the sides of their heads, like all other sharks. They are also called Angel Sharks.
- Heterodontiformes means “Different kinds of teeth”, and sure enough, these sharks have a variety of teeth so that they can grasp and crush shellfish.
- The Orectolobiformes are commonly called “Carpet Sharks” because their skin has nice patterns on it. The world’s largest fish, the Whale Shark, belongs in this group.
- The Carcharhiniformes are the most diverse group of sharks, with over 270 species. They have an extra set of eyelids to protect their eyes.
- The Lamniformes, also called Mackerel sharks, include the biggest cartilaginous fish ever, the Megalodon, as well as the most famous type of shark, the Great White Pointer. It also includes the harmless and very rare Megamouth Shark.
The Rays and Skates (Batoids) and the Sharks (Selachimorphs) are grouped together into a larger group called the Elasmobranchii.
What is the world’s largest cartilaginous fish?
The world’s largest living cartilaginous fish is a very gentle shark – the Whale Shark. Although it’s a shark, it’s very harmless – unless you are a tiny plankton or miniature squid! Despite eating such tiny things, it can grow up to 12 metres (about 40 feet) long or more – that’s twice as long as a Great White Pointer – and weigh around 12000 kg, or 26000 pounds!
The world’s largest ever cartilaginous fish is also a shark – but not one you would want to share the water with! The Megalodon or Megatooth Shark was similar to the famous Great White Pointer – except three times as big! At 18 metres (60 feet) long, its main food would have been Whale.