THE ANNALS AND MAGAZINE OF NATURAL HISTORY. [SECOND SERIES.] No. 28. APRIL 1850. XXII. — Notes on the Salmon and Bull-ti^out, By John Blackwall, F.L.S. In a short paper on the Salmon, Salmo salar, pubUshed in the 'Annals and Magazine of Natural History/ vol. xi. p. 409, I have endeavoured, on physiological principles, to establish the fact, that the growth of that valuable fish is not by any means so rapid as it is commonly supposed to be by ichthyologists. Ob-servations having relation to this subject and also to the oeconomy of the bull-trout, Salmo eriox, have been continued to be made, as suitable occasions presented themselves, up to the present period, on a plan similar to that previously adopted, and I am induced to insist upon the decided advantage which a recourse to physiological phsenomena possesses in investigations of this kind over the customary practice of mechanically marking fish as objects of experiment, in consequence of the various sources of error to which the latter mode of proceeding is exposed. Persons, in their endeavours to determine the rate of growth in fish by marking specimens, too frequently employ subordinate agents to carry their intentions into effect, to whom not only their system of marks is of necessity made known, but the anti-cipated result is also communicated. Now should it so happen that the agents are dependent upon their employers, or in any respect interested in making the event appear to coincide with their preconceived opinions, the desired object may be easily attained either by secretly marking specimens of a larger size than those which they were instructed and perhaps observed to select for the purpose, and by exhibiting them alone when re-captured, or by adapting the marks to fish subsequently taken, whose dimensions appear to be best suited to promote the end they have in view. Besides, it often happens that all the par-ticulars of the undertaking transpire, and becoming widely cir-culated, other parties resident in the neighbourhood may apply similar marks to fish of different sizes captured in the same Ann. ^ Mag, N, Hist. Ser. 3. Vol. v. 16
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