17) Characteristics of cartilaginous and bony fish.

CARTILAGINOUS FISH.

Cartilaginous fish are fish that have a skeleton made of cartilage, rather than bone. All sharks, skates, and rays are cartilaginous fish.

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.

Cartilaginous fish have entirely cartilaginous endoskeletons, meaning their skeletons are made from cartilage. They also have strong jaws, paired appendages, well-developed sense organs, and hunt using a system known as the lateral-line system, which uses vibrations to recognize prey. They can have placoid scales or be naked, and they do not have a swim bladder. They have a dorsal nerve cord that leads to a distinct brain, and they have a notochord.

• The internal skeleton of the cartilaginous fish is completely made of a flexible bone known as cartilage.

• The skeleton doesn’t have any ossified or rigid bone.

• These fish have a single or a pair of dorsal fins, an anal fin

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. Read more at Buzzle: http://www.buzzle.com/articles/cartilaginous-fish.html

BONY FISH.

Bony fish have a hard, bony plate, called an operculum, covering their gills. They may also have distinct rays, or spines, in their fins. About 90% of the world's fish species are bony fish.