Cartilaginous Fish

The ocean floor is one of the most fascinating habitats of all, with many colorful corals and schools of many fish. Fish are usually oval shaped, flattened either dorsal ventrally or sideways and spindle shaped. Fish also have a layer of scales that protect their bodies. Some fish have only cartilage (soft bone) while others have a vertebra or a back bone. Cartilaginous fish belong to the group of vertebrates that consist of fish like sharks, stingrays and chimeras.

Cartilaginous Fish Classification

• Kingdom: Animalia
• Phylum: Chordata
• Sub phylum: Vertebrata
• Infra phylum: Gnathostomata
• Class: Chondrichthyes
• Sub class: Elasmobranchii, Holocephali

Cartilaginous Fish Facts

There are many characteristics of cartilaginous fish that differentiate them from other species of fish.

• The internal skeleton of the cartilaginous fish is completely made of a flexible bone known as cartilage. The skeleton does not have any ossified or rigid bone.
• These fish have a single or a pair of dorsal fins, an anal fin, a pair of ventral fins that are supported by the girdles present in the internal skeleton and a single caudal fin.
• The swim bladder and lungs are absent and the liver is filled with oil to provide buoyancy to the body while swimming.
• The heart consists of two chambers like other fish and amphibians.
• The fish habitat consists of mostly creeks and rocks where they can get their prey easily. Sharks are mostly found near the seabed.
• These fish have jaws which have tiny teeth, with the upper row of teeth having a layer of enamel and the lower row of teeth is made up of bone tissue, which attaches them to the skin. The teeth are modified and are replaced by new teeth, when the older ones become worn out.
• There are many types of sharks like great white sharks and whale sharks to name a few. The skin of the sharks are rough and feel like sandpaper.
• Sharks and stingrays have an opening, called spiracle or gill slits that is situated on both sides of the head right behind the eyes, for breathing.
• The pectoral fins of the shark are called claspers and used for copulation. There are three ways in which sharks reproduce; oviparous, where the female lays eggs which takes a few months to develop, ovoviviparous, where the eggs are hatched in the oviduct and the embryo develops in the uterus and viviparous, in which the gestation period of the embryo is about one year.
• The sharks feed on other sea animals like zoo plankton, other smaller fish, whales and shellfish, etc.
• An interesting fact about sharks is that they have a huge mass and have to keep swimming continuously. If they stop swimming, they will sink like a stone.

Cartilaginous Fish vs Bony Fish

Approximately 400 million years ago, the ancestors of the bony fish and cartilaginous fish separated in the Silurian period. The bony fish belong to the class Osteichthytes and have a bone in their body, whereas cartilaginous fish are a family of Chondrichthyes, and have a skeleton made of cartilage. The bony fish have a pair of gills that are situated inside their bodies, and the cartilaginous fish have gill slits on the outer side of their bodies, present on both sides. In the latter fish species, the teeth, nostrils on the side of the head and the tiny tooth like scale are not fused together to the jaw. Fertilization of the eggs occurs through the process of internal fertilization unlike bony fish, where fertilization takes place outside the body.

Cartilaginous fish, especially sharks are ocean predators and are considered the king of the underwater world. Contrary to the popular belief as shown in movies, sharks only turn into man eaters, when they are provoked or when they sense a threat to their habitat.