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XXV. On theGromth and Migrations of the Sea-Trout oftheSolrcay (Salmo trutta). 

 By Mr JOHN SHAW, Drumlanrig. Communicated by JAMES WILSON, Esq., 

 F.R.S.E. 



(Read 27th March 1843.) 



ALTHOUGH the sea-trout (Salmo trutta} cannot be considered either of so much 

 importance to the community as an article of food, or so interesting in its habits 

 and economy to the naturalist as the true salmon, nevertheless, it is universally 

 allowed to rank next in value to that species. It holds a high place in the esti- 

 mation of the public as an article of diet, and is, consequently, an object of great 

 commercial value to our fisheries. Its history being still almost as involved and 

 obscure as was that of the salmon some seasons back, I am induced to offer the 

 following remarks with a view to its elucidation. 



From the circumstance of the sea-trout fry, in its earlier stages, bearing such 

 a marked resemblance to the young of the common river-trout (Salmo far io), en- 

 quirers, even of the closest habits of observation, have had much difficulty in 

 assigning to it any other place among our British Salmonidse than that of a mere 

 variety of the last named species. However, by proceeding on the mode of arti- 

 ficial or mechanical impregnation, the exact species of the parent fishes being pre- 

 viously ascertained, there can remain no doubt as to the identity of the progeny, 

 under whatever diversity of colour and markings they may shew themselves, in 

 then 1 progress to the adult state. 



It being a question among naturalists whether the so-called herling (Salmo 

 albus of Dr Fleming) is actually a distinct species, or only a certain progressive 

 state of the young of the sea-trout, I have taken every opportunity of determining 

 the question by marking the fins, &c., of a considerable number of these fishes for 

 several years, according as the seasons and conditions of the river enabled me to 

 obtain them ; and many specimens, as the details of my experiments will shew, 

 were taken and retaken, for several successive seasons, as common sea-trout, in- 

 creasing in dimensions from year to year. But as I now know the herling to be 

 only one of the links in the progressive chain, it will be better, instead of referring 

 separately to that state of the fish, to narrate the details of the several experi- 

 ments in the order in which the species advances in size, rather than that in 

 which the experiments upon their several stages were conducted. 



In consequence of experiencing much difficulty in capturing the parent sea- 

 trouts in the act of depositing then- spawn in the tributaries, I had recourse for 

 many years to the plan of taking them from the cruive on the river, during the 



VOL. XV. PART III. 5 G 



