Where is the largest reef in the world?

 

   Reef - the largest reef in the world is the Great Barrier Reef off the northeast corner of Australia. From Anchor Cay or island above the northern tip of Queensland, the reef runs parallel to the mainland at a a distance of about 60 miles, to Lady Elliot Island, 1,250 miles away to the south. This reef which is 80,000 square miles in area, was discovered in 1770 by Captain Cook. He called one of the many navigable passages Providential Channel after he had edged his ship through it to the coast. he named Endeavour Reef where he ran a ground after the ship itself. The fantastic coral forms give shelter to a collection of other living creatures such as fish, crustaceans, worms, molluscs and starfish, or greater variety than can be found anywhere else. Ninety per cent of the reef is under water and the remainder is composed of some 200 islands dotted along its length. A few of these islands remain permanently dry and swarm with bird life. They are used also by turtles who come ashore to lay their eggs. The Great Barrier Reef is a delicately balanced system suffering, from time to time an upset in its regular routine. Such an upset began in the 1960 with the invasion of the large poison spined starfish which is still going on. Appropriately called "crown of thorns", this starfish has infested some parts of the reef and by feeding on the polyps has ravaged vast areas of living coral. Even so the reef remains one of the most colourful regions of the world.   

What are fish scales?

Fish scales - are the remnants of the bony armour which enveloped the very earliest fish. Fish have scales as a protective coated for the skin. In fact, not all fish have them. But we usually think of a fish as a cold blooded, aquatic animal that swims by means of fins breathes by means of gills and is covered with scales. Scales may be of four different kinds placoid, granoid, cycloid and ctenoid. Placoid scales are long, spiny and toothlike, and the made of enamel and dentine. These are found on fishes which have a backbone made of gristle, such as sharks and rays. Ganoid scales are rather like placoid scales but are mainly bony and covered with kind of enamel called Ganoin. These think scales are found especially in garfish. Cycloid scales are thin, large, round or oval scales arranged in an overlapping pattern. They are found in carps and similar fishes.