GENERAL FEATURES 63 



this respect between the sea-trout of different rivers sufficiently constant 

 or pronounced to warrant them being classed as separate species, or 

 even races, neither Dr. Giinther nor his successor, Mr. George A. 

 Boulenger, would agree, and I see no good reason to differ from their 

 opinion. The fact, however, may have cumulative weight. 



As with the head so with the tail. I have already shown that, as 

 the sea-trout becomes older, the posterior margin of its tail tends to 

 become convex in outline, or, in other words, the hitherto square-ended 

 tail becomes round. The more pronounced tendency in this direction 

 in the sea-trout of the Tweed and some other East Coast rivers, and 

 the fact that such sea-trout are in general of a larger average size than 

 those of other districts, might point to the conclusion that they are older 

 fish, the roundness of the tail in the larger specimens having had longer 

 time to become accentuated. Careful examination of scales will settle 

 the question of age. Also one might infer that these so-called " bull 

 trout " are old fish, or at least that they have very frequently spawned, 

 from the fact that their flesh is always poor and white and very unlike 

 the rich condition of the flesh of the smaller and presumably younger 

 specimens. Scale examination will settle this point also. 



In this connection I am able to give, for purposes of comparison, 

 the diagrammatic outline of the tail of a 3^ lb. male sea-trout caught at 

 Luss in November, 1914, and of the tail of a 7 J lb. male " bull trout " 

 caught in the Tweed in the same spawning season (Fig. 19). The first 

 outline I took myself, and the second was kindly taken for me by a 

 member of the watching staff of the Tweed. One must admit that, 

 even taking account of the relative weights of these fish, there is an 

 essential difference in the outlines of the tails. Possibly, in the case of 

 each district, larger fish would show even more definite variation. 



I am not contending either way for differences discoverable 

 between these " bull-trout " of the Tweed and other rivers and the 

 sea-trout of other districts. But the facts point to differences 



