A LUMINOUS FISH.

Manawatu Herald, Volume XLVIII, Issue 3018, 1 April 1926, Page 4

A LUMINOUS FISH.

DISCOVERY IN IRISH WATERS.

Deep-sea hake trawlers ply their craft from the West of Ireland to Morocco, where the submerged edge of the continent begins to plunge down rapidly to the depths of the Atlantic Ocean. Mr. C. F. working as a naturalist on commercial trawlers, by the courtesy of their masters, has discovered a luminiferous fish with a hitherto un-, known type of light-producing organ, and has made some very interesting observations on it, published in the journal of the Marine Biological Association. The fish, known as Malacocephalus leaves, belongs to a small group of deep-water bony fishes generally with large head and whiplike tails. They seldom reach the surface alive, and so naturalists are acquainted with them chiefly fiom specimens preserved in spirit. The object of Mr. Hickling’s studies reaches a length of over a foot and a half, and comes up within 150 fathoms of the surface, so that it is often taken in the hake trawl, and although damaged, may stil be alive when emptied on the deck. The light-producing organ is a gland lying under the ventral surface of the body v between the pelvic fins some little way in front of the anal orifice. It position is marked by two triangular, nearly transparent and scaleless areas of skin. No light, however, is emitted through these. The gland, in Mr Hickling s opinion, is modified from the slimeproducing organs abundant in the skin of many kinds of fish, and the slimy secretion is discharged to the exterior by a duet which surrounds the anal orifice. Either by deliberate contraction of the muscles which surround the gland, or from the convulsions of dying fish, or perhaps only from pressure of other fish in the trawl, the secretion is discharged abundantly when the contents of the trawl are poured out on the deck. Ike smeared surface of the fish itself, the bodies of other fish with which it has been in contact, ropes,. tarpaulins, or the hands of sailors, glow with a blue light. When a still living fish is thrown back into the sea the secretion, as it spreads in the water, makes a glowing disc of light as large as a soup plate, behind which the creature disappears. By a rough-and-ready measurement the light was shown to have, a candle power of about .14., the print of a newspaper and the hands of a clock could be read by a solution of the secretion in water, and when held in the middle of a cabin, objects on the walls could be distinguished. NATURE OF THE LIGHT.

A number of experiments showed that the secretion itself was the source of the light, and not bacteria present in the slime, as in the case of not quite fresh fish, which are phosphorescent in the dark because they have been invaded by phosphorescent bacteria. All animal phosphjoresence is now supposed and nearly proved to be due to the presence of two substances, luciferin and lueiferase. The former is the fuel, which, when united with oxygen- to form oxy-luciferin, emits light and is used up in the process. Lueiferase is a ferment necessary to the oxydisation of the fuel. The ferment, like other organic ferments,, is permanently destroyed by heat under that of boiling water, but remains active in a solution which has ceased to give light when the luciferin has been burnt up and starts the emission of light again when added to a solution the luciferase of which has been destroyed by heat. Various tests made on the secretion by “Malacocephalus” showed that its light-producing properties are due to the presence of lucifcrase and luciferin.. It was noted, however, that it consumed rather an unusual quantity of oxygen, and that agitation of a fading solution, so bringing it in contact with a fresh supply of air, restored the luminescence. Those who have watched the phosphorescence of surface organisms from a steamer at night will recall how contact with the side of the ship, or still more the whirl of the screw, makes all the floating creatures flash out a medley of coloured light. Mr. Hickling suggests that the phosphorescence was at first, so to speak, an accidental by-product of the secretion of the slime glands of the skin. In its extreme development in the fish he has studied it may serve as a protective device, concealing the fish from its enemies in the fashion that squibs escape by clouding the water with discharges from their ink-sac. Possibly, also, it may serve to attract the food. The fish lives chiefly on Crustacea, and some of these are known to move towards sources of light.

In the case of most luminous creatures the light-producing substance is produced only in very minute quantities. In this ease each lish, when the abdomen is pressed, yields a large viscid drop of the greenishyellow slime. As the lishes themselves can be caught in great numbers (writes the scientific correspondent of the The Times), there seems to be an unusually favourable opportunity for the study of animal light. Mr. Hickling has shown the way, and it is to be hoped that research on an extended scale will be •carried out. The biological and chemical problems involved are more than sutlicient to justify this. But there might also be a practical result. In the forms of artificial light with which we are acquainted a large portion of the energy is transformed into heat instead of into luminous rays. This is not only extremely uneconomical, but

in most cases is of direct disadvantage. The light produced by phosphorescent organisms is a cold light —that is to say, only an insignificant part of the. energy is sidetracked as heat- rays. Announcements of the. artificial reproduction of animal phosphorescence have been made more than once, but so far they seem to have been premature. A knowledge of the exact nature of lueiferase might well lead to the use of fats and oils for illumination on a scale far more economical than any existing mode of employment.