IN TOUCH WITH NATURE

Otago Daily Times, Issue 21054, 17 June 1930, Page 2

IN TOUCH WITH NATURE

ELECTRIC FISHES. By J. Deummond, P.L.S., F.Z.S. Electric rays, or torpedo fishes, found iu New Zealand waters and in many other parts of the world, have living storage batteries, which look like honeycomb structures, usually at the side of the head. The electric organs arc tissues of inusclcs. The upper surface of the organ is .positive, the lower surface negative. There may be 400 prisms in the organ, each prism filled with a clear, trembling, jelly-like substance. An iron spear, a knife handle, or any other metallic conductor, may convey a shock. A large electric ray, it is stated, can give a shock sufficient to paralyse temporarily a strong man’s arm. The sensation is peculiar and unpleasant, but not dangerous. The batteries show all the known qualities of magnetism, rendering the needle magnetic, decomposing chemical compounds, and emitting sparks.

A shock is given by an electric ray voluntarily, presumably in defence against an enemy or to stun or kill prey. In soine rays the , electric organs are at the sides of the root of the tail. In other electric fishes they extend over the whole length of the tail. The strength of the shock increases with the number of electric plates included iu the circuit. The greatest shock by one species of electric fish is given when the fish’s body is curved, so that the head and the tail arc in contact with different points on the surface of another fish. The electric eel, the most powerful of the electric fishes, is not an eel, but an ecl-like ally of the catp. It lives in the': rivers of Brazil and Guiana. Its electric organs are in two pairs, one pair on the back of the fail, the other on.a fin, Each organ is composed of a great number of small cells. The star-gazer fish keeps its electric cells under the skin on the top of the head. An electric cat fish of the Nile; related to a cat fish introduced into New Zealand for food and sport, has electric organs all over its body. Like a garment, they cover the whole fish, which puts upon Itself an armour of light.

In addition to generating electric current, some fishes; develop organs to produce light. These organs- are developed independently in four groups of fishes, in no way related, to one ..another. The Organs' have' beeff stimulated by the application of electricity, although not electrical in principle. A midshipman fish of California was stimulated in this way. When a current sufficiently strong to pain the hands was applied the fish sent forth a, brilliant glow from every luminous organ. Lines on the surface of the body glowed with a brilliant light, which -continued while the stimulation was applied. A single well-developed light Morgan Und behind each; eye was particularly prominent. ’ The light was a. white one. When induced by electrical stimulation, it did not reach its maximum intensity suddenly, but come in gradually. When stimulation ceased it faded out in the same way. The light was merely strong enough for the observers to distinguish the apparatus used in the experiment.

The more complicated luminous organs possessed by fishes have lenses, and in that way resemble eyes, but they also have layers of cells that .contain a shiny substance, which makes the layers act like reflectors. On light being‘produced in the middle of an organ, the light that comes back against the reflector is shot forward and out through the lens, and all the light is concentrated in a beam.In addition to a reflector, each organ has an opaque screen, which protects the organs from a strong light, destructive to the tissues. There may be also colour screens. These allow only certain wavelengths.oL light, to pass,.giving: the, light a definite colour. A cuttlefish that lives in the ocean’s depths has luminous organs of three colours—blue, red, and violet.

Two species of fishes in the Dutch East Indies, having no luminous organs, but feeling the need for them,: have developed an organ to support luminous, bactqria. This is. a largo; organ, under each eye: The bacteria are - of a special kind. They do :nqt; grow on the surface of the fish. It seems to bo'another case of two different, kinds of organisms: living, together, for mutual benefit. . The .fish have the benefit of the light emitted by the bacteria, and the bacteria have a comfortable and cosy home, free-of charge. The light of these ■ bacteria shines by night and day. continually. The • fish have a black screen, like an eyelid, which they can drew over the organ, obscuring the light and making use of it only when desired. Fishermen cut off the organs, remove th screens, and use the organs for bait, the light shining steadily during a night’s fishing.’ These fish, syylm in the sea, turning! the fight on qnd off like any-fish that generate their nwn Tight.

A lantern-fish, Myctophum, which has relatives in New Zealand, is iridescent copper above and silvery below, not more than two inches long. About 450 of these mites, fully grown, would weigh a pound. Each has sufficient energy to keep 100 lamps alight. The lamps are small, round organs, scattered over the surface of the body, over the sides, near the head, ’and near the base of the tail. In an aquarium,' Mr,. W. Beebe, of New York, Saw a lower battery of lights, when going strong, east a solid sheet of light downward. Five times, he saw small-marine creatures go within range of the light and then turn and swim close to the brilliant la'ntern-fish, which, twisting round, seized some of the victims lured to destruction. When several lantern-fishes swam about, the portholes on their sides were almost always alight. They seem to be used at times as recognition signals, enabling members of a school to keep together, and showing stray individuals the way to safety.

A lantern-fish that exerted - itself unduly to get out of the way of another fish made its tail-lights Hash and die down in quick succession. Those lights flashed like heliographs. They were much stronger than the combined, steadier glow of all the other lights together, and their luminescence was a much deeper green. Luminescence in fishes is one of the most fascinating facts in natural history. It has attracted attention and curiosity, and several valuable monographs have been written on it, but they are insufficient to show the profoundly ‘ important part light plays in the lives of some fishes down there in the world of darkness.

Passing from creatures of the sea to creatures of the air, Mr J. B. Davcy, Pirongia, Waipa County, Auckland Province, lias sent a record of interesting observations on the tui’s notes. He has wandered through New Zealand forests for more than 50 years. Some 45 years ago, he lived at Featherston, where almost everybody whistled or hummed a melody that closely mimiced the tui’a notea in that district. Surveying close to the Tararua Range, not far from Dannevirkc, he found that the notes resembled “There is Nae, Luck About tile House.” Later, Mr Davey lived for ten years at Hikimutu, near Taumarunni. At first the tuis seemed to sing “ What Would You Do If You Married a Soldier?” At that time bo suspected that tuis had been given a lead or had picked up tunes casually. After listening for three years, it occurred to him that the tuis might be induced to change their tune. He had a splendid English concertina, with notes in the key of B flat singularly clear-cut, round, mellow and flute-like, and about the pitch of a .tui’a range. He played the opening notes of the song “Good News From Homo, Good Nows For Me.”