HE STALKS HIS PREY.

Auckland Star, Volume LXVIII, Issue 84, 10 April 1937, Page 4 (Supplement)

HE STALKS HIS PREY.

By E. G. TURBOTI, B.Sc

JOHN DORY.

ON Muriwai Beach I have ctten found large fishes, tall and very thin, which always have a kind of dark thumb-mark on their sides. There can be no mistaking creatures of iuch noticeable characteristics. They are John Dories, called by the Maoris kuparu. "John Dory" is, however, a name known throughout a large part of the world, for ite owner was familiar in the seas of Europe before he was

found in this country. Wherever he is he lives his life in the same interesting way. The first thing which you would notice if you were watching a living John Dory, would be his method of propelling himself. He does not drive through the water on a sideways movement of his tail and body as most fishes do. Instead, he keeps his body rigid, not moving it either to right or left. You notice, however, that his hind mid-fins, above and below, are waving constantly. Their movement keep him moving forwards, and his tail is free for use as a rudder, which is an unusual state of affairs among fishes. When we know something of the dory's way of feeding we see that this stiff-backed progress on a steady course is quite useful. He swims along not far above the ground and looks as if nothing could possibly excite him. Then he sights a small fish. Immediately he begins to stalk it very carefully. Now, to understand what he is doing, it is necessary for you to imagine meeting a dory head-on. You are in the place of the small

fish which the dory has decided to catch, and you see a kind of narrow, upright shadow coming nearer. There seems to be no need for alarm. Ni-ally, however, that «shadrwy line is the dory, who Ui too thin from aide to side to be very distinct from the front; and who is very wkely not making himself visible by flashing his tail about. Steadily, however, his fin-propel-lers drive him toward the unconscious small fish. As he approaches hie prey the dory shows signe of great excitement, his spiny back fin being erect as in the picture, and his colour changing rapidly from dark to light.

I At last lie is close enough to grab. Even now an alert little fish might escape but for another useful feature lof the dory. He has a mouth like elastic. He shoots it, out like a grasping tube and the small fish's doom is sealed. Too late it has fouud out the true nature of the shadowy line which approached it. Once a John Dory was seen to take a quite fresh dead fish into its mouth. This seemed to have been a great mistake, for the food was spat out again in great disgust. So it seems that this fish will not eat anything that does not move. The dead fish was probably rejected because it did not wriggle. It is worth while noticing ajrain the unusual nature of the .John Dory's "propeller." Most fishes move bv causinsr their bodies to wave from side to side in the water. The dory, however, really uses a kind of propeller, instead of emploving this scullintr method. In using' his midfins, above and below, to drive him along, the dorv resembles an even stranger fish—the sea-horse. (This creature has a single back fin, which performs 15 to 2i> shivering beats in every second.) On the whole this is not a verv speedy way of progressing. but it is very suitable for such fishes as these, which are not torpedo-shaped like their fast-moving cousins.