1.The skeleton of the cartilaginous fish is out of a flexible bone- cartilage. The skeleton does not have any bone.
2.These fish have dorsal fins, an anal fin, a pair of ventral fins and a single caudal fin.
3.The swim bladder and lungs are absent and the liver is filled with oil to provide buoyancy to the body while swimming.
4.The heart consists of two chambers like other fish and amphibians.
5.The cartilaginous fish habitat comprises mostly of creeks and rocks where they can get their prey easily. Sharks are mostly found near the seabed.
6.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.
7.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.
8.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.
9.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.
10.Approximately 400 million years ago, the ancestors of the bony fish and cartilaginous fish seperated 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 cartilaginous fish, 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.
11.Sharks occupy a variety of ecological niches, and the different species pursue a diversity of prey; from minute plankton and small invertebrates right up to large marine mammals. Some of the smaller reef sharks such as the Epaulette shark have narrow flexible bodies and strong pectoral fins that allow them to hunt through small crevices in coral reefs in pursuit of ‘cryptic’ prey. Such species occupy an ecological niche similar to the Moray eel
12.They occupy a huge range of ecological niches, from the huge, planktivorous Basking and Whale sharks to the bottom dwelling Carpet sharks, and probably the ultimate pelagic predator; the Great White shark.