THE SENSES OF FISH.
IN the winter season of hard frost the young fisherman, frozen out of all pursuit of his sport, may receive in one respect at least an object-lesson which should be of value to him when the angling season returns, and which cannot be conveyed to him so strikingly except in the frosty weather. The angler of experience is continually giving counsel to the tiro that in his passage up and down the river's bank, and especially when approaching a part of the stream in which he expects his fish to lie, he shall walk as far away as may be from the water, and shall approach it again, in order to throw his fly, in the most stealthy manner. It is not difficult for the tiro to understand that if ho marches along in full view of the fish in the stream the noble spectacle afforded them is likely to distract them from any interests of a gastronomic kind, and he is therefore ready enough to follow the counsel to keep himself as much concealed as possible ; but what it is not nearly so easy for him to realise is the equal necessity for the very stealthy, quiet approach, because it does not seem very evident to him how the beat of his foot on the earth can be communicated to the senses of the fish in the stream. Yet at a moment when the sides of the river are fringed with a coating of thin ice, stretching out as far from the bank as the current will permit it to solidify, some idea may readily be formed of the manner in which the footfall is communicated to the fish and how perfect a means of communication the water may afford. There is not much reason to suppose that fish are easily affected by noise,—in the ordinary sense, as an appeal to a distinct auditory organ. There is every reason, on the other hand, to believe them very keenly sensible to any vibration given to the element in which they live. The distance at which a dynamite cartridge exploded under water can communicate a fatal shock is testimony to it, and the fact that the impact of a bullet within a few inches of a pike lying on the surface is generally fatal points to the same conclusion. And when the ice is fringing the river it is scarcely possible to approach it with such gentle steps as to avoid causing it to tremble so as to send over the water circling waves extending outwards from the edge of the frozen surface. The elevation of the wave is very slight—
it is, of course, proportionate to the violence of the step, and the consequent movement imparted to the ice—but it is very perceptible from the bank, and on first seeing it it appears very remarkable and quite sufficient to account for the alarm of the fish. The landward edge of the ice, being attached to the land, receives and transmits any tremor of the ground, and it is singular that though the height from the ice- fringe to the bank on which the fisherman is walking may be several feet, the effect of the tremor should be so evident on the fluid surface of the water. It is not really right to dismiss the sense of hearing in fishes in the few words above. It has a claim to more attention, for though the question whether fish "hear," distinguishing this from the more general sensibility to vibration, is much debated, and would be more usually answered in the negative, there is no doubt whatever of the possession by certain fish of an extremely complicated apparatus, analogous to, and actually resembling, an ear. Neither is there the least doubt of the ability of some fish to emit various sounds, whence it is
argued that others of their kind must possess correlative auditory organs to receive the sounds; but there is perhaps a little too much a priori argument in this to carry great weight.
We have to remember, in any discussion of the senses of fish, that the fish family is a very large one and very various, some of its members living under conditions which differ very much from the circumstances of the lives of others. It is only reasonable to expect that the organs of the different senses should be modified in some accord with the conditions; and so we find it. It would be absurd to expect the organs which are sensitive to material vibrations to be the same in an animal which lived near the surface of the water, and in one which had its home in the lower depths of the sea, under great pressure. The life conditions of fish differ far more, for different species, than the conditions in which birds and mammals live, and it is therefore only natural that we should find far more difference in the sense organs of various fish than in those of other animals. With regard to the sense of sight, there is a vast difference in the different kinds. The salmon, trout, and most of the other surface-living fish are very keen-sighted, as the fisherman knows very well. Of course the angle of their vision is modified by the refraction of the water when it is directed towards the angler on the river's bank. They require a keen sight to find their food and to escape their foes,—otters, seals, and so forth. No doubt they see less far than a man, but far more minutely, especially in the water, and it has been practically proved of some species of sea-fish that their eyes are microscopic as compared with ours, for they are to be observed feeding on creatures and objects which we can only see with a rather high power of magnifying glass. But ordinary vision can be of comparatively little service to the fish which live in the great dark depths, and still less perhaps to those which find their food in the tangle of the seaweed forests. For them it is far more useful to have a very sensitive tactile apparatus and sense of smell ; and thus we find them with the vision but little developed. There is at least one kind which has fine powers of vision when young, in which state it is a daylight and surface feeder ; but in adult life it becomes a night feeder in the seaweed tangle, and in that state almost loses the use of its eyes. By compensation, infinitely of greater value, it develops sensitive tactile appendages about the head and lips. In fact, the case with fish is much as with ants, of which those that are of the " miner " kind, as it is called—that is to say, which live entirely in tunnels in the ground, like the small ,common ants of our fields—have very little power of vision, so far as we can perceive, in spite of their complicated eyes ; but they have a fine sensory organ, perhaps both olfactory and tactile, at the end of their mobile antennae, which must be of far more use to them in the dark than eyes could be. On the other hand, the wood ants, which go about their business out of doors in the full sunlight, see quite plainly a stick with which you menace them at the distance of a yard or so. The ability of even our most keen-sighted fish, such as our game fish, to distinguish colour has been much contested, even so good a field naturalist and observer as Sir Herbert Maxwell maintaining that they have not this faculty; but the great majority both of anglers and of naturalists seem disposed to think that an artificial fly which imitates the colour of the natural insect has a better chance of alluring a trout than one which merely imitates the form and disregards the colour.
The strictly tactile sense in fish appears, as a rule, to be much more localised, in such appendages as the barbels, than in most other animals. Generally speaking, the body of the fish does not seem to have much surface sensibility, and even the laceration caused by a hook swallowed far down affects sonic kinds with very little discomfort, although impalement by the book in the soft parts of the mouth evidently causes great agony.
To the present writer it seems very singular that much doubt should exist about the possession by very many fish of a keen olfactory sense. Izaak Walton knew something about it. He even sent a precious bottle, containing an oil which should attract the trout, to some old cronies, but he has to admit that the results of the trial which they made of it were rather negative. Old writers also used to tell us that the legs of the heron, as he stood in the water, exuded a flavour which was attractive to the fish and brought them close around him, so that he could spear them at pleasure with his pointed bill. In all probability this is only a pleasant fancy. It is hardly possible, however, to doubt that salmon are affected by the smell of a bottled prawn. Fish far away at the tail of the _pool sometimes appear to be pleasantly agitated by the effluvium almost as soon as the prawn is put into the water at the pool's head. The Cornishmen do not seem to have any doubt that the pilchards and mackerel are attracted for a,great distance by the smell of the olive seaweed spore. Many instances could be cited pointing to a like conclusion.
It has been conjectured that fish have also other senses, probably of an electric affinity, which we do not possess in any conscious degree, senses which perhaps make them cognisant of approaching changes of weather and are possibly useful as local guides. The "lateral lines" and their tubes have been even assigned as the special organs. Undoubtedly, in spite of the comparative insensibility of the body surface of fishes, most of them have a marked tendency to photo-dermatism. Few subjects of a like kind are more interesting than the investigation of the senses of fishes, and there are few which give the worker a larger field, or one more suggestive of far-reaching speculations. It is among its merits that it compels him to rid himself of many of his preconceptions in regard to the rigid limits of the different senses generally recognised in the higher animals; and, quite apart from any objective result which he may arrive at, no effect can be more beneficial than such an extension of the mental outlook.
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