WHAT FISH SEE.

Hokitika Guardian, 5 January 1922, Page 1

WHAT FISH SEE.

What, does, a. fish see in its world under the water and of the outside world above it?. What is this under-water world like, and how does the angler appear to the fish. By the use of glass-fronted observation chambers, and with the knowledge that the eye of the fish differs only from the eye of the human in that, tjie fish is a little more short-sighted, these questions can bo easily answered, writes Laurence Easterbrook in the “Daily Mail.” The first thing, that must be realised is that the surface of, the water, when viewed from underneath, or, from the fish’s point of view, the “ceiling,” becomes an extensive mirror reflecting the river bottom. Except for a small hole, or “skylight,” in this ceiling, the fish sees nothing of the world outside. ITe only sees the river bed below him reflected above in its natural colour. So it is that the world under the water is usually green in colour owing to the reflection of the vegetation growing on the river bottom. But there is, for the fish, a circular hole immediately above him in the “ceiling,” through which lie can see objects in the world outside. Those directly overhead .appear normal, bin objects seen through the “skylight” at an angle appear dwarfed and distorted, and suspended in the air. The “skylight” is separated from the shrrouiuling surface by a ring of iridescent colours. The explanation of this - “skylight” is that only rays of light that strike the surface of the water at a certain angle reach the fish’s eye. Other rays are reflected or refracted away so that they do. not come to it. The size of the “skylight” varies with the position of the eye of the observer. It a depth of 9ft the circumference of the hole is 54ft. At 3ft the circumference is 9ft, and as the observer approaches the surface the hole gradually diminishes and disappears. It is only through this “skylight-,” then, that the eye of the fish can detect the fisherman. Outside its radius he is concealed. What does he look like from the fish’s -point of : view ? If his clothing blonds with the hushes, trees, or buildings beyond, his image above the arc ol the “skylight’ is not easily detected. Bold “camouflage” patterns of clothing would be quite useful if an angler frequently fished in front of the same background. But if be stands behind a bush apd pokes his head and shoulders over the top, then the fish can see him plainly and will give him a wide berth. If the angler is standing in the water in waders, the result is peculiar, for fish sees the submerged part of him rip #to bis waist, blit nothing of the rest of bis body that is above the surface; the submerged legs are also reflected on the “underneath” side of the surface of the water, so that an inverted image of the angler’s legs ns far as bis waist is imposed on top of the ienl legs and waist directly seen. The result is like two pairs of legs cut off, and the one pair put- on the top of the othei;, with a common waist- The heron and other “wading birds make use of this ontical law to catch their prey. The : fish only sees their thin, spindly legs standing in the water and the reflected image of them (for their bodies aie •above and invisible), and these legs are easily mistaken for twigs undergrowth. But the heron is watching from above, still, and ready to strike.. The fish comes a little too near the undetected legs, and with a lightning flash the heron darts its head beneath tlie surface and seizes its victim in its beak.