OF all animals living fish are probably the most brilliantly coloured. Many have the power of changing colour, in some cases very rapidly. It is impossible to describe adequately the immense variety and striking colour effects present in some species. At the other end of the scale may be placed the uniform sombreness of certain fish inhabiting the depths of the sea.
Fish possess great variety of bodily shape. Compare, for instance, the serpent-like eels with the flattened skates and rays living on the sea-bottom, or the spherical globe-fish with the strange rectangular coffer-fish. In some fish there is great disproportion between the parts of the body, the head usually being the most varied in appearance. Mention may be made of the phosphorescent organs of some deep-sea fish, which enable them to find their prey in the dark abysses they frequent.
Contrary to general belief, certain fish are capable of producing sound, in some cases by rubbing together bony joints, or grating their teeth, or through muscular control of the air bladder. The sound has been described as a deep drumming, whilst in other cases it is like the grunting of a pig-
THE SIX BRANCHES OF THE FISH FAMILY
FISH have been divided into six orders :
2. LAMPREYS AND HAG FISH.
3. BONY FISH.
4. GANOID FISH.
5. SHARKS AND RAYS.
6. MUD FISH.
The first two orders have no biting jaws, but have instead a highly specialised tongue in the form of a rasp. The lancelet is the only representative of its order; it is a very curious
animal, of exceedingly simple construction, found in sandbanks, especially in the Mediterranean. It is transparent, pointed at both ends, about two inches in length, with hardly a vestige of brain. The lampreys and hags are also very primitive—they are eel-like, slimy creatures with rudimentary eyes.
The bony fish are comparatively modern, but they are now the dominant class and the most numerous. This order includes most of the edible fish with which we are familiar. In their case the skeleton, instead of remaining more or less gristly throughout life, is more or less bony. In one small group the gills are arranged in a little tuft instead of in the usual form of plates. To this group belong the sea-horses, often seen in aquariums. They have the additional curious feature that the male has a sort of pouch, into which the eggs are placed by the female, and to which the young can retreat when threatened by any danger. Another species is just like a piece of seaweed in appearance, whilst the pipe fish, one species of which is British, are an allied group.
The sturgeons make up the majority of the fourth order. They are large fish inhabiting the rivers and seas of the north temperate zone. They have rows of large, bony shields on the body; the mouth is toothless and the upper lobe of the tail is the larger one. This order has declined in numbers in recent geological times.
GIGANTIC TERRORS OF THE DEEP
THE sharks and rays constitute an order whose members have no swimming bladder. Some species bring forth their young alive. With the sharks there are often many rows of teeth, which are continually growing forward to replace the outer rows as they are worn out. Owing to the position of the mouth, a shark may have to turn over when seizing any animal—a man, for example—swimming on the surface, but this is not its normal method of feeding. Many sharks have been accused of man-eating when doubtless not guilty, but the big White Shark, which grows so long as forty feet, is one of the terrors of the sea.
Some species are truly remarkable, as for instance the Thresher or Fox Shark, which is distinguished by the great length of the upper lobe of the tail fin. This is often as long as the rest of the body, the creature measuring about fifteen feet in all. It is inoffensive as regards man, but is a voracious
destroyer of other fish, and has been known to attack whales. Extraordinary, too, are the Hammer-headed Sharks, which have the head prolonged horizontally on either side, with the eye at the end of each lobe. They often attain a length of fifteen feet.
The Basking Sharks include the largest of all living fish, specimens measuring fifty feet in length being known. They have, however, small teeth and are harmless to man. The Dog Fish are also of the Shark family. They are much smaller, and the British species are familiar to fishermen by whom they are much disliked owing to the damage they cause to the nets.
The true Saw Fish are also remarkable. They measure ten to twelve feet long, their ‘saws ‘being six feet by a foot across the base. By powerful strokes of this weapon they are capable of lacerating the bodies of other animals and tearing off pieces of flesh to devour.
The Skates are allied to the Rays. Some of the Rays carry terrible stinging spines at the end of a long, whip-like tail. This, joined to their enormous size, makes them truly fearsome creatures.^ The giants of the race are found in the West Indies, and are often known as ‘Sea-bats ‘or ‘Devil-fish.’ They sometimes measure twenty feet across. At times they rise out of the water and for a short time skim along through the air; when they fall back into the water, the sound is like the firing of a cannon.
Lastly there is a decreasing and intermediate order, the mud fish of the Amazon and Australia. At certain seasons these fish burrow in mud, breathe through their lung, and can exist a long time without water.