106 DEPARTMENT OF THE NAVAL SERVICE 



8 GEORGE V, A. 1918 



" It is interesting to observe that, although this fish enjoyed steady hand feed- 

 ing, it had only attained one-tenth of the weight it would, in all probability, have 

 reached had it spent the last four years of its life in the natural manner in the sea, 

 and the scales show that the feeding has been, as one might expect, of a regular 

 character, and it would be impossible to estimate the age in the regular way. The 

 absence of a spawning mark is at first sight particularly striking, although this is 

 not so surprising when one remembers that a great deal of the erosion of scales takes 

 place after the fish has ceased feeding and left the sea, and while it is in the river 

 before spawning." 



Masterman^ makes reference to salmon that were bred in tanks at the Plymouth 

 Marine laboratory. He says : " Through the courtesy of Dr. Allen, the Director of 

 the Plymouth Marine laboratory, I was enabled to examine the scales of young salmon 

 which were bred in the tanks, and for two successive seasons were ' stripped ' of ripe 

 ova and milt. Their scales show no trace of worn edge or of spawning mark." He 

 gives a photograph of a scale of one of these salmon (see fig. 27)- 



Similar experiments have been carried on with the British " sea-trout ", the 

 migratory trout of the British coasts, the name applied to it by those who consider the 

 " brown trout ", said to be non-migratory, a different species and even by those who 

 think the two are of the same species, developed under different conditions. Tate 

 Regan'* definitely states " In the British Isles there is only one species of trout." 

 Lamond^ gives an approving review of the arguments presented by Regan and in dis- 

 cussing one of these, viz., that sea trout, if prevented from going to the sea, will live 

 and breed in fresh water, makes reference to an experiment carried out at Howietoun 

 under the supervision of the hatchery superintendent, John Thompson, whose notes are 

 recorded thus : " The parents were caught in a tributary of the river Forth, brought 

 to Howietoun and spawned on November 23, 1886. There were 450 ova laid down to 

 hatch of which some 350 hatched out successfully in February, 1887, and the fry (some 

 250) were shifted from the hatchery house to one of our ponds, in June of the same 

 year and then fed the same as other fry. The young fish were again shifted into a 

 larger pond in June, 1888, when the average size was found to be about three inches. 

 In August, 1889, some specimen fish, about six inches in length, were taken from the 

 pond by Dr. Day for examination and comparison with common trout, S. fario, and 

 we were all agreed that it was impossible to distinguish them by the eye from S. fario. 

 In April, 1890, the fish were again moved to another pond and I spawned some of the 

 females in November of the same year, crossing the ova with milt from S. levenensis 

 and S. fontinalis. A few fry of the former were hatched out and reared but were after- 

 wards mixed with other fry. The remainder of the parent sea-trout were afterwards, 

 I think, turned out into a reservoir, when about five years old. They never attained to 

 any great size." 



In all the cases mentioned, apparently the only difference observed between the fish 

 retained in fresh water and those normally migrating is the difference in size, the 

 retained specimens growing much more slowly than the normal migrating specimens- 

 The scant supply of food in the fresh water as compared with the supply in the sea, 

 which is commonly given as the reason for the slower growth in fresh water, appa- 

 rently cannot be the controlling cause in all of these cases, since in some of them at 

 least the fish may have been fed as much as they wished for. Possibly the lack of any 

 necessity for special activity in search for food accounts for a similar lack of appetite 

 and a sluggishness^ in digestion and a general condition that is not conductive to rapid 

 growth. This would also account for any differences in external appearance and in 



3 Masterman, A. T. Report on investigations upon the salmon with special reference to 

 age determination by study of scales, Fishery Investigations, Board of Agriculture and Fisheries, 

 series I, Vol. I, 1913, p. 31, London. 



4 Regan. C. Tate. The Fresh Water Fishes of the British Isles, 1911. 

 SLamond, Henry. The Sea Trout, 1916. 



