How Fishes Feed Epicurian Oysters and Omnivorous Shrimps

Sun (Auckland), Volume 1, Issue 4, 26 March 1927, Page 17 (Supplement)

How Fishes Feed Epicurian Oysters and Omnivorous Shrimps

(Written for THE SUN".)

Vast though the sea may be, it is crowded with a myriad forms of life, the most pressing need of each member of which is to find food. The struggle for existence is largely a struggle for food, and the problem of obtaining this has been solved in the most diverse ways by different animals, so that there is practically no conceivable source of food which has not been utilised by some creature or other. Particularly in the waters near the shore the sea is always rich in tiny particles, both animate and inanimate. If the former, they may be either plant or animal —microscopic fragments of living matter —either fully grown or the eggs of larger animals or seaw'eed spores. Many animals feed exclusively on this type of diet. Fishes' Sorting Organs. Sponges (which are really animals) do this, their bodies being honeycombed with canals which are lined with fine threads, the lashing of which creates a continuous current of water in at one part of the sponge and out at another. Shellfish, such as oysters and mussels, possess a very elaborate ar }d beautifully efficient apparatus within the shell which causes a current of water to flow over a fine network that allows the water to pass through but retains all solid particles, which are gently wafted to the mouth by vast numbers of minute, vibrating hairs. Round the mouth are a pair of sorting organs which reject the larger particles and pass the smaller to the mouth. There are certain worms which live in self-constructed tubes of sand, limestone, or mud. They cannot leave these tubes, and so must take such food as comes to them in the water. Around the mouth they carry a crown of delicate, feathery filaments, often very beautifully coloured, which are pushed out through the open ends of the tubes within which they are withdrawn in a flash on the approach of an enemy. These tentacles are covered with a slimy substance that entangles all minute particles, and with microscopic hairs the movement of which carries the food to the mouth. Tentacles as Food Ladles. The little sea cucumbers (near relatives of the starfish), which live in holes and fissures in rock, also carry a crown of foliaceous tentacles round their mouths. These also are covered with slime in which food collects, but Lhere are no moving hairs to carry this to the mouth: instead each tentacle is curled inward and pushed to its full extent within the mouth, which shuts tightly around it so that the food is left behind as the tentacle is slowly pulled out. One tentacle after another is pushed into the mouth and sucked clean—exactly like a child sucking jam off its fingers! The mud that covers the bottom of the sea in many regions provides food for many sluggish beasts which spend

their lives ploughing through it, swallowing as they go large quantities from which they extract such nourishment as it contains. The limpet, which browses on the rocks, obtains its food by scraping off the seaweed that grows upon them. It does so by the aid of a long horny ribbon bearing a series of fine teeth, which it pushes against the food and draws backwards and forwards so that the w r eed is rasped off and carried to the mouth. The sea-urchin takes the same kind of food as the limpet, but bites off the weed with five long teeth which are supported in a very intricate skeleton known, on account of its discoverer and shape, as Aristotle’s lantern. The muscles which work the lantern force the teeth downwards so that they all come together beneath the mouth, biting off a circular piece of weed, which is pushed into the mouth. Careless Shrimps. Creatures such as crabs, lobsters, prawns, and shrimps are far from particular on what they feed. All is grist that comes to their mill, being seized by their large claws and passed on to a series of complicated jaws which tear it to pieces before passing it into the mouth. Their near relations, the barnacles, literally kick food into their mouths: being attached they do not need feet to walk with, but use them instead as a kind of net which is jerked out of the shell and then drawn in with the contained food. The octopus and squid seize their victims by the suckers on their tentacles, kill them by squirting poison over them, and then tear them open with horny jaws shaped like a parrot’s beak. Starfish, though slow, are powerful and persistent creatures, and by exerting a steady pull can finally open the shell of a large mussel. They have no jaws, and must swallow their prey whole, and, if it is too large to be swallowed, with great resource they protrude the stomach through the mouth and around the food! Whales’ Microscopic Prey. Finally, there are the whales, with or without teeth. The toothed spermwhale takes the largest prey of any animal known, feeding on the gigantic and little-known cuttlefish which inhabit deep seas. These have never been seen intact, but from the stomach of a sperm-whale taken by the Prince of Monaco a single tentacle was taken which “though incomplete from being partly digested, still measured twentyseven feet in length.” The toothless whales, on the other hand, feed on minute animals which float near the surface of the sea, straining water continuously through their mouths and collecting the tiny animals on the frayed edges of the whalebone plates which hang down from the roof of the mouth. Amongst this type of whales are the largest animals in the world, so that we have the striking paradox j of the greatest of creatures feeding on i microscopic prey.