ON MALFORMED TROUT FROM SCOTTISH WATERS 



99 



3. The Docked-tailed condition consists in a malformation of 

 the caudal fin-rays. The condition of these rays is not quite the 

 same in the Carron specimens as in those from Islay and Kirkcud- 

 brightshire, inasmuch as in the latter the minute dichotomisation of 

 the fin-rays is destroyed, whereas in the former it largely persists. 



4. The caudal is not the only fin liable to be affected by this 

 condition. It is generally shared in by the anal fin, frequently also 

 by the pectorals, more rarely by the ventrals. 



5- 



The dorsal fin is normal in every specimen I have seen. 



Theories as to Causation. 



The theories which have been hazarded regarding the cause of 

 the docked-tailed condition may be enumerated as follows : — 



1. That it may be caused by impurities contained in the water 

 in which the fish live. 



2. That it may be the result of mechanical injury ; either by the 

 fish nibbling each other's tails, or by friction against rocks or stones. 



As regards the first of these supposed causes, the late Mr. F. 

 Day in his "Fishes of Great Britain and Ireland" (vol. ii. p. 102), 

 observes that the " tailless " condition " in some streams has been 

 traced to be due to the action of deleterious matter in the water 

 (see 'Angler's Note Book,' 1880, p. 66)." Further, quoting from an 

 unpublished note by Mr. Harvie-Brown, he goes on to say that this 

 gentleman "observed about 1876, in the River Carron, that a 

 contraction of the rays of the tail fins of the trout commenced, due 

 it was universally believed to the action of deleterious matter in the 

 water, through the agency of paper mills." I see from Mr. Harvie- 

 Brown's notes, to which he has so kindly given me access, that he 

 was also at one time inclined at least to suspect that the docked 

 condition of the Gonar Burn trout was due to the stream having 

 been poisoned by washings from lead mines. As to the pollution 

 of the River Carron below Denny, there is unfortunately no room for 

 doubt, though, unless corroborated by numerous other similar 

 instances, it does not follow that this is the cause of the malforma- 

 tion of the trout-tails. Accordingly, with a view to testing the 

 Gonar Burn case, Mr. Harvie-Brown had an analysis of the water 

 made by Mr. J. Falconer King, Edinburgh City Analyst, the results 

 of which, expressed in grains per imperial gallon, are as follow : — 



Carbonate of Lime . 2.06 



Carbonate of Magnesia . 0.55 



Sulphate of Lime . . O.68 



Sulphate of Magnesia . 1. 17 



Sulphate of Soda . . o. 1 7 



Chloride of Sodium . 0.92 



Nitrate of Soda . . trace 



Nitrites . . . none 



< >xide of Iron . . none 



