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A very accurate and ingenious Observer has thus mentioned his remarks upon the migration, &c. of
There is (says this Gentleman) one other fish common in this Country that is migratory, when in a situation to admit of it: this is the Eel. Eels can live and breed in stagnant ponds from which there is no outlet, as Carp, Tench, and several other fishes do; but whether they ever there attain the same perfection as under other circumstances may, perhaps, be doubtful. In what place the Eel deposits its young in preference to others, when at perfect freedom; or whether the young fry make a progression towards the Sea, as the Salmon does at a certain period of its growth, I cannot tell. But in one particular case I know, and it has been observed by others, that in the month of June, yearly,
the Skin will be found covered with exceeding small ones, ranged in a very orderly manner. To obtain these from the Skin, take a piece of the skin which grows from the side of the Eel, and while moist spread it on a piece of Glass, that it may dry very smooth. when thus dried it will appear all over dimpled, or pitted by the Scales, which lie under a sort of Cuticle, this thin skin may be raised with the sharp point of a pen-knife together with the Scales, which will then easily slip out. It has been asserted, from trials of this nature, that very few Fishes, except such as have Shells, are destitute of Scales.
To prepare Scales of Fishes for Examination with the Microscope, they should be taken off, if possible, with nippers, and be soaked in water for a day or two, and afterwards carefully rubbed to clear them from the Skin and Dirt which may adhere to them; they should then be placed in smooth paper, between the leaves of a Book, to make them dry flat, and prevent their shrivelling up.
immense swarms of young Eels make a progress from the lower part of the river towards the higher, with a quickness and unremitted assiduity that are surprising. This Phenomenon was remarked in the river Dee, in Aberdeenshire. The Eel is a fish that seems (unlike the Trout) to dislike running streams, and therefore avoids that part of the river where the Current is strong. It had, probably, been this circumstance that induced them, in the rapid Dee, to direct their progress only along the Edges of the river close to the banks.
A Line followed the windings of the River, being often suddenly deflected by Stones or other Interruptions without any breach of its continuity. This line having frequently caught my eye, my Hand was put into the Water to touch the Line, with a view to examine what it was: the Line became discontinued, when my hand approached; but it united again as soon as my hand was withdrawn. This induced a nearer examination; and I then perceived, with astonishment, that this Line was formed by a series of small Eels, moving forward with great celerity. These Eels did not exceed half an inch in length, but were in all respects perfectly formed like the common Eel. The line might, perhaps, on an average, consist of from twenty to thirty in breadth, and the individuals being in different degrees of forwardness, and close to each other, made the Line uniform. The progress with which they advanced, was not less than four miles an hour: and this continued for eight Days and Nights together; and there was no apparent diminution of it when I left the place.
There was a similar Line on the opposite side of the River. The water in which they floated at the place where I observed them was in general about two or three inches deep.
From the above Statement, it may safely be computed that the numbers which must have thus passed amounted to many Myriads. What becomes of such multitudes of Fishes we may conjecture, but never perhaps shall be able to ascertain.
The above Observations (continues this Gentleman) respect the spontaneous movements of Eels upwards in rivers; those that follow, indicate their similar progress downwards at one Season of the Year. In Scotland, in the neighbourhood of Linlithgow, is a considerable Lake, in which great quantities of Eels are caught, by hooks and lines during any of the Summer months; but the principal fishing is in the month of October, when it is found that the Eels, directed by natural Instinct, discover an irresistible propensity to issue from the Loch by the passage through which the water flows from it to the Sea. In October the person who rents the Fisheries puts into that passage a kind of Chest, so formed as to allow free passage to the water, while it stops those Eels that exceed a certain size. This Chest is every morning emptied of its fish, which are sometimes in such abundance as to require Carts to carry them away. This fishing continues about a month; before or after which time few or none can be so taken; the Chest is then removed, and the passage left freé.
In Wiltshire, about Warminster, where the Rivers
are small, and more rapid in their course than in many other parts of England, the Mills placed on the Streams are numerous, and the water is carefully directed into one Channel. The persons possessing these Mills having discovered that numbers of Eels go down the river during every Flood, happening in October, have devised a Box, which they call an Eel-grate; this is placed in a convenient part of the River, and thus great quantities of Eels are caught. They also find, that no Eels worth mentioning can be taken in this way at any other Season of the Year.
Whether the Eels thus caught in descending the River are near the breeding time, as the Salmon are which ascend the same small Streams, has not been ascertained. Probably they are; if so, they are not, like the Salmon, lean, but fat, and in good condition. It is probable that these Eels, after depositing their young near the mouths of the Rivers, ascend the Rivers again at another Season of the year, till they regain their former haunts, although there are not the same facilities for discovering their progress upward, were it even certain, as for that in their descent. They may have been at first entangled in their descent in Baskets or Nets whose Mouths were placed towards the Current. This could not be done in their Ascent; and although devices called Cruives have been invented for catching Salmon in Ascending the Rivers, yet the progress of Eels in that direction having not been remarked, no Contrivance for thus catching them has been devised.
It might be possible, by watching the time the
large Eels return, to devise contrivances for stopping them in their Ascent somewhat similar to the Salmon Cruives, which might be done at a trifling expence, upon those small rills especially that communicate with swamps or lakes; for though the Banks were overflowed during floods, yet if these Eel-traps occupied the full width of the rill, when in its usual state, no loss could be sustained during floods, as the strength of the Current would at that time interrupt their progress upwards. It is very probable, that if the large Eels do return, they may do it more leisurely than they descend, especially where the Water runs dead; therefore, in brisk running Streams we shall most likely discover the circumstances that affect these Migrations.
It may be proper also to remark, that if the conjecture respecting the general periodical Migrations of this Fish be well founded, it ought to follow, that fewer Eels should be found in those Lakes where the Water, issuing from them, falls over a steep Rock, forming a deep Cascade, than in others where the communication with the Sea is more free; because, though the Eels might be precipitated over it in their descent, the young fry would be there interrupted in their attempts to ascend it. Such is the case with Loch-schin, a large fresh water Lake in the Shire of Sutherland, in Scotland. Can any one (asks this Gentleman) inform me whether Eels abound in that Lake or not, and whether those there found are in any respects distinguishable from others? It is not asked if there be any Eels in it, for there will doubtless be some; but the question is, are there as