THE question of the powers and limitations of the organs of sight in fish, and the extent to which they enable them to discriminate between colours, is an interesting and difficult problem, appealing strongly to the fisherman as well as to the naturalist.

As in all questions connected with the investigation of the life-history of fish, the matter is rendered all the more difficult by the fact of their inhabiting a different medium from ourselves. Nevertheless the experienced angler who is also an observant man,—and the two are not necessarily always synonymous,—must have often had opportunity of noting facts throwing light on some aspects of the question.

From the point of view of the fisherman the sense of sight of fishes, and particularly of the Salmonidae, is doubtless of much importance. That their eyesight is acute, to an extent that is proverbial, needs no demonstration. The veriest tyro, as he passes along the banks of a clear trout-stream, will soon learn this elementary fact for himself. As his education proceeds, he will also speedily note that the trout's range of vision is chiefly forward and upward ; and lying, as they necessarily do when at rest, with their heads up-stream, he finds that to approach within reasonable distance unseen he must keep down-stream from them and as low as possible. This is the foundation of the first principle of clear-water stream fishing, wading upstream.

A much more intricate and difficult question is that as to the power of discrimination of colour by fish. Do they perceive the differences of colour; if so in what degree ; and do these colours produce the same effect on the fish's as upon the human eye? It is permissible to assume that as fishes see, partly, at least, through a different medium, the resultant impressions received by them will vary from that in our own experience. In the case of the angler's fly, it will be generally seen by the fish against the sky, that is, against the source of light; and if we hold a salmon-fly, however gaudy and brilliant, between our own eyes and the sky, we find but a dark silhouette appearing, with possibly reflected rays of coloured light from hackle-fibre or tinsel ; but all the meticulous minutiae of the fly-dresser have disappeared.

Half a century ago the salmon flies of the Tweed, and generally throughout Scotland, were sombre affairs, as is seen by the patterns of Stoddart and others ; black, red or claret rnohair or pigswool, a hackle dyed or plain, a turkey, mallard or teal wing, with perhaps a little tinsel. But Stoddart thought it wiser that the tinsel, if used, should be tarnished. When later the fashion of using the bright, so-called Irish, flies came in, the solemn warning was given that the fish were being frightened back into the sea.

To-day the gaudy fly reigns almost indisputed. Yet there are many anglers, and these not the least experienced, who hold that if the old quiet patterns were once more fished as assiduously as the new the results would be much or quite the same; that the 'best fly,' in fact, is still that which is oftenest and longest in the water.

Formerly there were few professional tackle-makers. Flies were dressed by the angler himself or obtained from the local semi-professional who, in the days of unprotected waters, was everywhere to be found. These naturally used the materials readiest to hand, and the results being satisfactory, they were content. The increase in the ranks of fishermen, consequent on increased travelling facilities, changed all that, and much else. New men brought new ideas, new materials, new experiments.

A fisherman, however, is not necessarily a logician. He fishes, we will say, with a certain fly without success; changes it for something different in colour, and lo! fish after fish succumbs to its attractions. What more can he wish? Of course the fly has done it.' It does not seem to occur to him that had he continued to fish with No. 1 the result might, very possibly at least, have been the same. In fact we have here simply the old problem of post hoc or Propter hoc.

As a rule gillies and boatmen are very opinionative as to the patterns that alone, according to them, are of any use in their particular waters, and for the sake of peace it is as well, perhaps, to give in to their prejudices. Should the angler, however, persist in the use of some unorthodox lure and achieve success, he must by no means assume that he has thereby converted his attendant, who will believe, and probably assert, that had his advice been followed the bag would doubtless have been doubled.

It is not always so, however ; there are some in the ranks, more especially among the younger and better educated, who have profited by experience and observation, as in the following instance, which took place some years ago on a well-known stretch of the Aberdeenshire Dee. Pool after pool had been fished in vain, and a new cast having been reached the old vexed question was discussed with the gillie, who on that famed water had assisted at the death of hundreds of salmon.

One of the most successful salmon fishers of the last generation, as the result of the experience of a long life-time on Tay and Tummel, latterly confined himself strictly to a single pattern of salmon-fly, dressed by himself. It was a thin, light-blue floss-silk body ribbed with tinsel, and a light wing of mixed fibres.

When we come to consider trout and troutflies, the question is in one way different; for whatever salmon-flies, so-called, may be supposed to represent, they certainly bear no resemblance to flies; whereas trout-flies are presumed to be imitations of natural insects, at least in so far as river-fishing is concerned. One might therefore suppose that here, at least, the matter of colour must be all important, always assuming that trout have the power of colour discrimination; and in the view of the `Dry-fly purist,' as he loves to be termed, it is taken for granted that it is so. One has only to study the very interesting text-books of Mr. Halford, for instance, to find that the most delicate shades of colour in silk, hackle or wing are strenuously insisted on.

Let us look, however, for a moment on the other side of the shield, and recall the most interesting and practical experiments of Sir Herbert Maxwell, well known as an angling expert, an observant naturalist, and one endowed to an unusual degree with the faculty of critical analysis and deduction. The results of his experiments are embodied in a report published in the Field of 19th June, 1897. As all readers may not have access to it, a short summary may be of interest. Sir Herbert had some May-flies dressed in the ordinary way, except that they were dyed of a brilliant scarlet or blue ; and with these he proceeded to fish during the May-fly season in a well known southern trout stream noted for its large and wary trout. Beginning with the usual more or less exact copy of the natural insect, with which he caught several trout, he then proceeded in bright sunshine to cast a scarlet fly over a rising fish; it was at once accepted, and a fine trout landed-all doubtless to the utter astonishment of the attendant keeper. The same fly was then presented to another trout, with the same immediate result. A brilliant blue May-fly was mounted and just as greedily taken by another victim ; and so on throughout a most successful day, when some thirty trout, none under a pound in weight, were landed, of which nine weighing 13 1/2 lbs. were kept. Of the thirty a few were caught on the usual imitation ; the rest took the gaudy scarlets and blues, some of which eccentric-looking patterns are now before me. Sir Herbert then gives in detail a second and equally successful experiment in another river, where trout up to 2 or 3 lbs. in weight fell victims to the same unorthodox flies.'

Against this instance may be given an experience of the writer's, which seems to point in the opposite direction. Fishing a number of years ago on the River Deveron, a big rise of fly came on suddenly, and large trout were at at once rising in a 'boil' in all directions; but, as so often happens in such circumstances, they would not look at the artificial flies offered to them. After several changes, a cast of Yorkshire hackles was tried with gratifying success, and a nice basket of good average size was secured. But every one of these was taken on one particular fly, the so-called `partridge and blue.' This fly, moreover, was not at the end of the cast of four flies-usually the most killing position-but higher up.

This was thought at the moment to be a great discovery, and many 'blue partridges' were sent for; but never again was it found to be of much, or any use. Now all the other flies on the cast were likewise Yorkshire hackles of exactly the same size and pattern, save only colour, and all were patterns of proved value as killers on Deveron; so wherefore the preference for that particular blue? To the writer the riddle remains unsolved.

On the point in question, Mr. J. A. HarvieBrown says:' 'Trout show decided preferences, for colours (at least educated trout).' That writer's opinion on any subject connected with Angling or Natural History must carry great weight, although in this instance running counter to the experience of Sir Herbert Maxwell, as given above.

To leave the Salmonidae for the moment, and to turn to the pike, it seems to have been long generally held that a `bit of red' about the bait often proved enticing. We have all seen the tuft of red wool so frequently tied round the end triangle of a spoon. In corroboration of this theory a friend recently related the following instance to me. During a visit to Loch Awe, trout fishing being 'off,' it was resolved to make a raid in the loch upon the pike, of of which there are only too many for the wellbeing of the nobler species. Two rods were equipped, the one with an ordinary brown phantom, the other with a red one-at one time, if memory serves, esteemed to be 'good medicine' for salmon in Loch Tay.

The pike proved to be in taking humour, and the result was something like nine or ten of good average weight. But every one of these was caught on the scarlet bait ; the other, with exactly the same chance, did not elicit so much as a casual `offer.' It is, perhaps, worthy of notice that a pike following a spinning bait will see it more or less on its own level and often against a background, say of weeds or shore ; and this is also true to some extent in the case of the salmon, which frequently follows the fly a long way before making the final dash. Whereas, as a rule, the trout must see the fly against the sky and light, presenting therefore only a dark outline.

The same friend was good enough to call attention to a passage in Herbert Spencer's Autobiography, bearing on the subject under consideration:

`My constitutional tendency to call in question current opinions, was manifested when fishing, as on other occasions. While in Wales the year before, occupied in writing on Psychology and occasionally casting a fly over a stream or llyn, it occurred to me that, considering how low is the nervous organization of fishes, it is unlikely that they should be able to discriminate so nicely as the current ideas respecting artificial flies imply-unlikely, too, that they should have such erratic fancies as to be taken by combinations of differently coloured feathers, like no living creature ever seen.

`I acted upon my scepticism, and ignored the local traditions. Hearing me vent my heresies, the farmer, tenant of Beoch, challenged me to a competition. It was scarcely a fair one, for my flies, made by myself without practice, were, of course, ill-made, and the bungling make of them introduced an irrelevant factor into the competition. Notwithstanding this, however, fishing ,from the same boat we came back ties ; showing that the local flies had no advantage.

`I may add here that in subsequent years I systematically tested this current belief in local flies; and on various lochs and four different rivers found it baseless. This experience furnished me with a good illustration of the uncritical habits of thought characteristic, not of the common people only, but of those who have received University educations. For in every case I have found highly cultivated men -professors and others such-accepting without hesitation the dogmas of keepers and gillies concerning the flies of the river. Always their assigned reason is that these dogmas express the results of experience.

'But inquiry would show that those who utter them have never established them by comparisons of numerical results. They simply repeat, and act upon, what they have been told by their predecessors; never dreaming of methodically testing their predecessors' statements by trying, whether, all other things being equal, other colours and mixtures of colours would not answer as well. The delusion results from pursuing what, in inductive logic, is called the method of agreement, and not checking its results by the method of difference.’

This passage emphasises admirably the vague attitude of thought of even educated men on such questions, and the fallacy of drawing general or universal conclusions from isolated and exceptional instances. If we are to arrive at a more exact apprehension of the powers and limits of the vision of fish, and of the impressions produced in them by colours, we must first have a series of long and carefully conducted experiments. The results, duly noted and tabulated, would form a ground-work for investigations that should lead to conclusions of greatest interest to anglers and naturalists.