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

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.