Trout always have a recognised home of their own, inhabited by a pretty fixed15 number of individuals. But if you catch the two sole denizens16 of a particular scour17, you will find another pair installed in their place to-morrow. Young fry seem always ready to fill up the vacancies18 caused by the involuntary retirement19 of their elders. Their size depends almost entirely upon the quantity of food they can get; for an adult fish may weigh anything at any time of his life, and there is no limit to the dimensions they may theoretically attain6. Mr. Herbert Spencer, who is an angler as well as a philosopher, well observes that where the trout are many they are generally small; and where they are large they are generally few. In the mill-stream down the valley they measure only six inches, though you may fill a basket easily enough on a cloudy day; but in the canal reservoir, where there are only half-a-dozen fish altogether, a magnificent eight-pounder has been taken more than once. In this way we can understand the origin of the great lake trout, which weigh sometimes forty pounds. They are common trout which have taken to living in broader waters, where large food is far more abundant, but where shoals of small fish would starve. The peculiarities21 thus impressed upon them have been handed down to their descendants, till at length they have become sufficiently22 marked to justify23 us in regarding them as a separate species. But it is difficult to say what makes a species in animals so very variable as fish. There are, in fact, no less than twelve kinds of trout wholly peculiar20 to the British Islands, and some of these are found in very restricted areas. Thus, the Loch Stennis trout inhabits only the tarns24 of Orkney; the Galway sea trout lives nowhere but along the west coast of Ireland; the gillaroo never strays out of the Irish loughs; the Killin charr is confined to a single sheet of water in Mayo; and other species belong exclusively to the Llanberis lakes, to Lough Melvin, or to a few mountain pools of Wales and Scotland. So great is the variety that may be produced by small changes of food and habitat. Even the salmon25 himself is only a river trout who has acquired the habit of going down to the sea, where he gets immensely increased quantities of food (for all the trout kind are almost omnivorous), and grows big in proportion. But he still retains many marks of his early existence as a river fish. In the first place, every salmon is hatched from the egg in fresh water, and grows up a mere26 trout. The young parr, as the salmon is called in this stage of its growth, is actually (as far as physiology27 goes) a mature fish, and is capable of producing milt, or male spawn28, which long caused it to be looked upon as a separate species. It really represents, however, the early form of the salmon, before he took to his annual excursion to the sea. The ancestral fish, only a hundredth fraction in weight of his huge descendant, must have somehow acquired the habit of going seaward—possibly from a drying up of his native stream in seasons of drought. In the sea, he found himself suddenly supplied with an unwonted store of food, and grew, like all his kind under similar circumstances, to an extraordinary size. Thus he attains29, as it were, to a second and final maturity30. But salmon cannot lay their eggs in the sea; or at least, if they did, the young parr would starve for want of their proper food, or else be choked by the salt water, to which the old fish have acclimatised themselves. Accordingly, with the return of the spawning31 season there comes back an instinctive32 desire to seek once more the native fresh water. So the salmon return up stream to spawn, and the young are hatched in the kind of surroundings which best suit their tender gills. This instinctive longing33 for the old home may probably have arisen during an intermediate stage, when the developing species still haunted only the brackish34 water near the river mouths; and as those fish alone which returned to the head waters could preserve their race, it would soon grow hardened into a habit engrained in the nervous system, like the migration35 of birds or the clustering of swarming36 bees around their queen. In like manner the Jamaican land-crabs37, which themselves live on the mountain-tops, come down every year to lay their eggs in the Caribbean; because, like all other crabs, they pass their first larval stage as swimming tadpoles38, and afterwards take instinctively39 to the mountains, as the salmon takes to the sea. Such a habit could only have arisen by one generation after another venturing further and further inland, while always returning at the proper season to the native element for the deposition40 of the eggs.
These trout here, however, differ from the salmon in one important particular beside their relative size, and that is that they are beautifully speckled in their mature form, instead of being merely silvery like the larger species. The origin of the pretty speckles is probably to be found in the constant selection by the fish of the most beautiful among their number as mates. Just as singing birds are in their fullest and clearest song at the nesting period, and just as many brilliant species only possess their gorgeous plumage while they are going through their courtship, and lose the decoration after the young brood is hatched, so the trout are most brightly coloured at spawning time, and become lank41 and dingy42 after the eggs have been safely deposited. The parent fish ascend43 to the head-waters of their native river during the autumn season to spawn, and then, their glory dimmed, they return down-stream to the deep pools, where they pass the winter sulkily, as if ashamed to show themselves in their dull and dusky suits. But when spring comes round once more, and flies again become abundant, the trout begin to move up-stream afresh, and soon fatten44 out to their customary size and brilliant colours. It might seem at first sight that creatures so humble45 as these little fish could hardly have sufficiently developed aesthetic46 tastes to prefer one mate above another on the score of beauty. But we must remember that every species is very sensitive to small points of detail in its own kind, and that the choice would only be exerted between mates generally very like one another, so that extremely minute differences must necessarily turn the scale in favour of one particular suitor rather than his rivals. Anglers know that trout are attracted by bright colours, that they can distinguish the different flies upon which they feed, and that artificial flies must accordingly be made at least into a rough semblance47 of the original insects. Some scientific fishermen even insist that it is no use offering them a brown drake at the time of year or the hour of day when they are naturally expecting a red spinner. Of course their sight is by no means so perfect as our own, but it probably includes a fair idea of form, and an acute perception of colour, while there is every reason to believe that all the trout family have a decided48 love of metallic49 glitter, such as that of silver or of the salmon's scales. Mr. Darwin has shown that the little stickleback goes through an elaborate courtship, and I have myself watched trout which seemed to me as obviously love-making as any pair of turtle-doves I ever saw. In their early life salmon fry and young trout are almost quite indistinguishable, being both marked with blue patches (known as 'finger-marks') on their sides, which are remnants of the ancestral colouring once common to the whole race. But as they grow up, their later-acquired tastes begin to produce a divergence50, due originally to this selective preference of certain beautiful mates; and the adult salmon clothes himself from head to tail in sheeny silver, while the full-grown trout decks his sides with the beautiful speckles which have earned him his popular name. Countless51 generations of slight differences, selected from time to time by the strongest and handsomest fish, have sufficed at length to bring about these conspicuous52 variations from the primitive53 type, which the young of both races still preserve.
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1
trout
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| n.鳟鱼；鲑鱼(属) | |
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poultry
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| n.家禽，禽肉 | |
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specimens
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| n.样品( specimen的名词复数 )；范例；（化验的）抽样；某种类型的人 | |
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versed
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| adj. 精通，熟练 | |
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attained
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| （通常经过努力）实现( attain的过去式和过去分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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attain
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| vt.达到，获得，完成 | |
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abjure
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| v.发誓放弃 | |
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brooklet
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| n. 细流, 小河 | |
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bask
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| vt.取暖，晒太阳，沐浴于 | |
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dart
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| v.猛冲，投掷；n.飞镖，猛冲 | |
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tickling
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| 反馈，回授，自旋挠痒法 | |
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entirely
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| ad.全部地，完整地；完全地，彻底地 | |
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philosophical
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| adj.哲学家的，哲学上的，达观的 | |
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intrusive
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| adj.打搅的；侵扰的 | |
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fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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denizens
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| n.居民，住户( denizen的名词复数 ) | |
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scour
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| v.搜索；擦，洗，腹泻，冲刷 | |
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vacancies
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| n.空房间( vacancy的名词复数 )；空虚；空白；空缺 | |
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retirement
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| n.退休，退职 | |
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peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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peculiarities
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| n. 特质, 特性, 怪癖, 古怪 | |
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sufficiently
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| adv.足够地，充分地 | |
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justify
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| vt.证明…正当(或有理)，为…辩护 | |
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tarns
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| n.冰斗湖，山中小湖( tarn的名词复数 ) | |
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salmon
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| n.鲑，大马哈鱼，橙红色的 | |
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mere
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| adj.纯粹的；仅仅，只不过 | |
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physiology
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| n.生理学，生理机能 | |
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spawn
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| n.卵，产物，后代，结果；vt.产卵，种菌丝于，产生，造成；vi.产卵，大量生产 | |
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attains
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| （通常经过努力）实现( attain的第三人称单数 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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maturity
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| n.成熟；完成；(支票、债券等)到期 | |
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spawning
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| 产卵 | |
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instinctive
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| adj.(出于)本能的；直觉的；(出于)天性的 | |
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longing
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| n.（for）渴望 | |
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brackish
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| adj.混有盐的；咸的 | |
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migration
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| n.迁移，移居，（鸟类等的）迁徙 | |
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swarming
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| 密集( swarm的现在分词 )； 云集； 成群地移动； 蜜蜂或其他飞行昆虫成群地飞来飞去 | |
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crabs
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| n.蟹( crab的名词复数 )；阴虱寄生病；蟹肉v.捕蟹( crab的第三人称单数 ) | |
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tadpoles
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| n.蝌蚪( tadpole的名词复数 ) | |
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instinctively
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| adv.本能地 | |
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deposition
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| n.免职，罢官；作证；沉淀；沉淀物 | |
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lank
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| adj.瘦削的；稀疏的 | |
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dingy
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| adj.昏暗的，肮脏的 | |
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ascend
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| vi.渐渐上升，升高；vt.攀登，登上 | |
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fatten
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| v.使肥，变肥 | |
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humble
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| adj.谦卑的，恭顺的；地位低下的；v.降低，贬低 | |
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46
aesthetic
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| adj.美学的，审美的，有美感 | |
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semblance
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| n.外貌，外表 | |
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decided
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| adj.决定了的，坚决的；明显的，明确的 | |
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49
metallic
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| adj.金属的；金属制的；含金属的；产金属的；像金属的 | |
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50
divergence
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| n.分歧，岔开 | |
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51
countless
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| adj.无数的，多得不计其数的 | |
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52
conspicuous
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| adj.明眼的，惹人注目的；炫耀的，摆阔气的 | |
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53
primitive
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| adj.原始的；简单的；n.原(始)人，原始事物 | |
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