Because the drought and heat of summer render the streams unfit for their reception. At this period they crowd, in shoals, towards the coast, and roam about the estuaries, until the autumnal floods again entice them to enter the rivers.
Because they there make a bed by the parent fish working up against the stream, the spawn being deposited in the gravel and covered at the same time. The bed sometimes reaches from twelve feet in length to ten in breadth. The process frequently occupies more than a week; during which the eggs deposited by a single fish sometimes amount to 20,000. This spawning season extends from the end of October to the beginning of February, and, according to very satisfactory evidence, it occurs about the same time throughout all the rivers of the United Kingdom. The eggs of the salmon remain in the gravel for several months, exposed to the influence of running water. In the course of the month of March, and nearly about the same period in all our rivers, the fry are evolved. When newly hatched, they are scarcely an inch in length, of the most delicate structure, and for a while connected with the egg. Upon leaving the spawning bed, the fry betake themselves to the neighbouring pools, where they speedily increase to two or three inches in length. In April, May, and June, they migrate towards the sea, keeping near the margin, or still water, in the river, and when they reach the estuary, they betake themselves to a deeper and more sheltered course, and escape to the unknown haunts of their race, to return shortly after as grisles, along with the more aged individuals. All these seaward migrations of the parent fish and the fry, are influenced and greatly accelerated by the occurrence of the floods in the rivers. - Quarterly Review.
Because the turn of the salt water brings up aquatic insects, and perhaps small fish; and it is supposed that salmon know this, and search for food at a time when it is likely to be found. - Salmonia.
Because the breeding fish and the helpless fry maybe preserved and protected.
Because it has large blue or olive bluish marks on the sides, as if they had been made by the impression of the fingers of a hand.
Because, in the physical constitution of these animals, their production is diminished as their food is small in quantity. The ova of the large and small trouts are of the same size; but in the large trout there are tens of thousands, and in the small one rarely as many as forty.
Trouts vary in size, from the great lake trout, weighing above 60lb. or 701b. to that of the brook, which is scarcely larger than the finger.
Because fresh-water trout are somesimes carried in floods to the sea, and come back larger and altered in colour and form, and are then mistaken for new species ; and as each river possesses a variety belonging to it, this, with differences depending upon food and size, will, it is thought, account for the peculiarities of particular fish, without the necessity of supposing them distinct species. The same holds good with regard to salmon. - Salmonia.