18 THE FISHING INDUSTRY 



in such a way that it becomes practically invisible 

 when seen from above or below, the under-surface being 

 silvery white, and the upper surface generally olive or 

 blackish-green. Sometimes, as in the mackerel, the 

 upper surface is mottled, resembling rippled water. 



Most small fish in ponds and streams reflect their 

 surroundings so well, and are coloured and marked in 

 such a way, that they are almost invisible to the large 

 fish, for example pike, that prey upon them. Generally, 

 they reveal their presence by the flash of light reflected 

 from above by their scales, as they turn suddenly to 

 snap at a morsel of food. In the same way, many 

 predatory fish, e.g. the angler fish, resemble their 

 surroundings so closely that the fish for which they are 

 lying in wait swim within easy reach of them without 

 perceiving their danger. Many fishes, particularly 

 in tropical waters, are remarkable for their bright and 

 gorgeous colouring. It is impossible to preserve 

 these colours in their natural brightness after the fish 

 have been taken from the water, but amongst the 

 brightly coloured corals, and anemones and seaweeds, 

 in the crystal clear water of their natural environment, 

 they flit like gorgeous tropical birds in a tropical forest. 



Distribution. Fishes are found in practically every 

 ocean, lake and river in the world, with a few notable 

 exceptions, such as the Dead Sea, in which the con- 

 centration of salt is too high. They appear to exist 

 at all depths of water, and have been found in the sea 

 as deep down as 2,720 fathoms. Fish living at this 

 depth generally possess enormous mouths, long, attenu- 

 ated, soft bodies, and are equipped with highly developed 

 phosphorescent organs. 



The distribution of a particular species appears to 

 depend upon the salinity of the water, the temperature 

 of, the water, the kind and quantity of food available 



