On the 1st of November 1839, this ingenious observer perceived a pair of sea-trouts engaged together in depositing their spawn among the gravel of one of the tributaries of the river Nith, and being unprovided at the moment with any apparatus for their capture, he had recourse to his fowling-piece. Watching the moment when they lay parallel to each other, he fired across the heads of the devoted pair, and immediately secured them both, although, as it afterwards appeared, rather by the influence of concussion than the more immediate action of the shot. They were about six inches under water. Having obtained a sufficient supply of the impregnated spawn, he removed it in a bag of wire gauze to his experimental ponds. At this period the temperature of the water was about 47°, but in the course of the winter it ranged a few degrees lower. By the fortieth day the embryo fish were visible to the naked eye, and, on the 14th January, (seventy-five days after deposition,) the fry were excluded from the egg. At this early period, the brood exhibit no perceptible difference from that of the salmon, except that they are somewhat smaller, and of paler hue. In two months they were an inch long, and had then assumed those lateral markings so characteristic of the young of all the known Salmonidæ. They increased in size slowly, measuring only three inches in length by the month of October, at which time they were nine months old. In January 1841, they had increased to three and a half inches, exhibiting a somewhat defective condition during the winter months, in one or more of which, Mr Shaw seems to think, they scarcely grow at all. We need not here go through the entire detail of these experiments.[23] In October (twenty-one months) they measured six inches in length, and had lost those lateral bars, or transverse markings, which characterise the general family in their early state. At this period they greatly resembled certain varieties of the common river-trout, and the males had now attained the age of sexual completion, although none of the females had matured the roe. This physiological fact is also observable in the true salmon. In the month of May, three-fourths of the brood (being now upwards of two years old, and seven inches long) assumed the fine clear silvery lustre which characterises the migratory condition, being thus converted into smolts, closely resembling those of salmon in their general aspect, although easily to be distinguished by the orange tips of the pectoral fins, and other characters with which we shall not here afflict our readers.
The natural economy of the sea-trout thus far approximates that of the genuine salmon, but with the following exception. Mr Shaw is of opinion that about one-fourth of each brood never assume the silvery lustre; and, as they are never seen to migrate in a dusky state towards the sea, he infers that a certain portion of the species may be permanent residents in fresh water.[24] In this respect, then, they resemble the river-trout, and afford an example of those numerous gradations, both of form and instinct, which compose the harmonious chain of nature's perfect kingdom. In support of this power of adaptation to fresh water possessed by sea-trout, Mr Shaw refers to a statement by the late Dr McCulloch, that these fish had become permanent inhabitants of a loch in the island of Lismore, Argyllshire. Similar facts have been recorded by other naturalists, though, upon the whole, in a somewhat vague and inconclusive manner. We have it in our power to mention a very marked example. When certain springs were conducted, about twenty years ago, from the slopes of the Pentland Hills, near Edinburgh, into that city, which Dr Johnson regarded as by no means abundantly supplied with the "pure element of water," it was necessary to compensate the mill-owners by another supply. Accordingly a valley, (the supposed scene of Allan Ramsay's "Gentle Shepherd,") through which there flowed a small stream, had a great embankment thrown across it. After this operation, of course the waters of the upper portion of the stream speedily rose to a level with the sluices, thus forming a small lake, commonly called the "Compensation Pond." The flow of water now escapes by throwing itself over the outer side of the embankment, which is lofty and precipitous, in the form of a cataract, up which no fish can possibly ascend. Yet in the pond itself we have recently ascertained the existence of sea-trout in a healthy state, although such as we have examined, being young, were of small size. These attributes, however, were all the more important as proving the breeding condition of the parents in a state of prolonged captivity. It is obvious that sea-trout must have made their way (in fulfilment of their natural migratory instinct) into the higher portions of the stream prior to the completion of the obstructing dam; and as none could have ascended since, it follows that the individuals in question (themselves and their descendants) must have lived and bred in fresh water, without access to the sea, for a continuous period of nearly twenty years. This is not only a curious fact in the natural history of the species, but it is one of some importance in an economical point of view. Sea-trout, as an article of diet, are much more valuable than river-trout; and if it can be ascertained that they breed freely, and live healthily, without the necessity of access to the sea, it would then become the duty, as it would doubtless be the desire, of those engaged in the construction of artificial ponds, to stock those receptacles rather with the former than the latter.[25]
Having narrated the result of Mr Shaw's experiment up to the migratory state of his brood, we shall now refer to the further progress of the species. This, of course, we can only do by turning our attention to the corresponding condition of the fry in their natural places in the river. So far back as the 9th of May 1836, our observer noticed salmon fry descending seawards, and he took occasion to capture a considerable number by admitting them into the salmon cruive. On examination, he found about one-fifth of each shoal to be what he considered sea-trout. Wisely regarding this as a favourable opportunity of ascertaining to what extent they would afterwards "suffer a sea change," he marked all the smolts of that species (about ninety in number) by cutting off the whole of the adipose fin, and three-quarters of the dorsal. At a distance, by the course of the river, of twenty-five miles from the sea, he was not sanguine of recapturing many of these individuals, and in this expectation he was not agreeably surprised by any better success than he expected. However, on the 16th of July, exactly eighty days afterwards, he recaptured as a herling (the next progressive stage) an individual bearing the marks he had inflicted on the young sea-trout in the previous May. It measured twelve inches in length, and weighed ten ounces. As the average weight of the migrating fry is about three and a half ounces, it had thus gained an increase of six and a half ounces in about eighty days' residence in salt water, supposing it to have descended to the sea immediately after its markings were imposed. In this condition of herlings or phinocks, young sea-trout enter many of our rivers in great abundance in the months of July and August.
On the 1st of August 1837—fifteen months after being marked as fry, on its way to the sea—another individual was caught, and recognised by the absence of one fin, and the curtailment of another. This specimen, as well as others, had no doubt returned, and escaped detection as a herling, in 1836; but it was born for greater things, and when captured, as above stated, weighed two pounds and a half. "He may be supposed," says Mr Shaw, "to represent pretty correctly the average size of sea-trout on their second migration from the sea." In this state they usually make their appearance in our rivers, (we refer at present particularly to those of Scotland,) in greatest abundance in the months of May and June. This view of the progress of the species clearly accounts for a fact well known to anglers, that in spring and the commencement of summer, larger sea-trout are caught than in July and August, which would not be the case if they were all fish of the same season. But the former are herlings which have descended, after spawning early, to the sea, and returned with the increase just mentioned; the latter were nothing more than smolts in May, and have only once enjoyed the benefit of sea bathing. They are a year younger than the others.
As herlings (sea-trout in their third year) abounded in the river Nith during the summer of 1834, Mr Shaw marked a great number (524) by cutting off the adipose fin. "During the following summer (1835) I recaptured sixty-eight of the above number as sea-trout, weighing on an average about two and a half pounds. On these I put a second distinct mark, and again returned them to the river, and on the next ensuing summer (1836) I recaptured a portion of them, about one in twenty, averaging a weight of four pounds. I now marked them distinctively for the third time, and once more returned them to the river, also for the third time. On the following season (23d day of August 1837) I recaptured the individual now exhibited, for the fourth time.[26] It then weighed six pounds." This is indeed an eventful history, and we question if any Salmo trutta ever before felt himself so often out of his element. However, the individual referred to must undoubtedly be regarded as extremely interesting to the naturalist. It exhibits, at a single glance, the various marks put upon itself and its companions, as they were successively recaptured, from year to year, on their return to the river—viz. 1st, The absence of the adipose fin, (herling of ten or twelve ounces in 1834;) 2dly, One-third part of the dorsal fin removed, (sea-trout of two and a half pounds in 1835;) 3dly, A portion of the anal fin clipt off (large sea-trout of four pounds in 1836). In the 4th and last place, it shows, in its own proper person, as leader of the forlorn hope of 1837, the state in which it was finally captured and killed, of the weight of six pounds. It was then in its sixth year, and, representing the adult condition of this migratory species, we think it renders further investigation unnecessary.
From these and other experiments of a similar nature, which Mr Shaw has been conducting for many years, he has come to the conclusion, that the small fry called "Orange-fins," which are found journeying to the sea with smolts of the true salmon, are the young of sea-trout of the age of two years;—that the same individuals, after nine or ten weeks' sojourn in salt water, ascend the rivers as herlings, weighing ten or twelve ounces and on the approach of autumn pass into our smaller tributaries with a view to the continuance of their kind;—that, having spawned, they re-descend into the sea, where their increase of size (about one and a half pound per annum) is almost totally obtained;—and that they return annually, with an accession of size, for several seasons, to the rivers in which their parents gave them birth. In proof of this last point, Mr Shaw informs us, that of the many hundred sea-trout of different ages which he has marked in various modes, he is not aware that even a single individual has ever found its way into any tributary of the Solway, saving that of the river Nith.