Whale shark (Rhincodon typus). The whale shark, found in tropical seas, is the world's largest fish, reaching an average length of 8 metres. It is harmless to humans, moving slowly through the water as it uses specially adapted gill arches to filter the water, removing anything edible. Its 1.5 metre diameter mouth can circulate up to 6000 litres of water an hour. It is thought to live to an age of 60-150 years. Photographed in the Gulf of California, Mexico.