VI. Salmo trutta, or Trout.
A number of varieties of trout have from time to time been introduced into New Zealand, such as Salmo fario, or brown trout; Salmo levenensis, or Loch Leven trout; Salmo samardii, variety, Scotch burn trout; Salmo trutta, sewen, sea trout, or white trout. Probably some of the ova originally brought out was crossed more or less with a strain of the Salmo eriox, or bull trout.
All these fish are gradually accommodating themselves to their new environment, and becoming very like the varieties found in corresponding northern latitudes—say, in Switzerland and northern Italy. Our Lake Wakatipu trout are almost identical with the trout I saw taken in the northern Italian lakes in nearly similar latitudes, and very much alike in their habits.
I believe, myself, that the varieties and hybrids of Salmonidæ called “trout” are merely one species, subject to animmense amount of variation, many of the larger forms of which seek their food, whenever conveniently situated, in the ocean, and run up the rivers like salmon to perpetuate their
species; but it is probable that they do not make such lengthened journeys at sea as the salmon proper are supposed to do, but frequent the shallower water on the coast.
Even within the limits of a single species (so-called) no two are found to be exactly similar, but there is a tendency to diverge from the original type in such direction as to preserve and increase useful varieties—a law of variability by adaptation, which is destined to modify every organism so as to fit it for new conditions of existence. A notable instance of this occurs in the gillaroo trout of Ireland, which have developed quasi-gizzards to enable them to crush and digest the small fresh-water snails and shells found in certain lakes. It will be interesting to watch whether similar developments are found in any of the varieties in our lakes at the antipodes.
In short, my theory is that, whatever variety we liberate of the ordinary species of trout, it will develope into a Salmo novæ-zealandiæ, suited to the water in which it is liberated, and corresponding with trout in similar latitudes in the Northern Hemisphere more closely than with the varieties found in the more northern latitudes of our Mother-country. I do not think that these fish will retain the characteristics of the variety found in the environment from which they were taken, and consider that the results already obtained in New Zealand have proved this.