Note (return) — NATURAL HISTORY OF SALMON AND SEA-TROUT.

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