Arthur. — On the Brown Trout introduced into Otago. 505 



also frequently seen the upper lobe larger than the under one. The least 

 depth of the tail is pretty constant, being from a tenth to a twelfth of the 

 total length of the trout, or about that ratio. 



But, as the size of the fins is thought by naturalists to have a direct 

 relation to the depth of water and nature of the bottom, it may be well to 

 see what evidence my specimens can give on that point. Dr. Giinther 

 says : — " Those individuals which live in rapid streams, being in almost 

 constant motion, and wearing off the delicate extremities of the fins, have 

 the fin-rays comparatively shorter and stouter, and the fins of a more 

 rounded form, particularly at the corners, than individuals inhabiting ponds 

 or lakes." * The number of trout I have measured with particular reference 

 to this question is not, in my opinion, sufficient to test the case fairly in 

 Otago waters. Out of 13 rivers, I have had 19 males and 6 females under 

 measurement, also 2 males from Lake Wakatipu ; these are all. I have 

 classified them, however, distinguishing fish from rapid and rocky streams, 

 as separated from those frequenting larger and stiller water ; and I find 

 that the evidence is very puzzling and contradictory, so that different 

 theories might easily be based on particular cases. I have therefore pre- 

 pared a large table, showing the ratio which each fin bears to the total 

 length of the fish — measuring the base of the single or median fins and the 

 longest ray of the double fins, as representing the lengths. The result on 

 the whole, and taking it for what it may be worth, is corroborative of the 

 above quotation from G-iinther. Three of the fins, viz., the dorsal, pectoral, 

 and ventral, I find shorter in the rough, quick-running rivers, than in the 

 stiller, heavier streams, or in the lake ; but the anal is doubtful. While, 

 therefore, my experiments on this point are not so complete as could be 

 desired, they have brought out other facts curious and interesting, and 

 which are not so open to dubiety. Thus I find the females have all smaller 

 fins than the males, excepting the anal, which is larger. Then, among the 

 females, the range of difference or variation in the size of fins is very great 

 as between different individuals, and also between the different fins of the 

 body themselves. But, among the males, the range is not nearly so great ; 

 neither is there the great difference of size between the body fins them- 

 selves. These latter facts will appear more clearly from this short 

 table : — 



Range in ratio of fins to total length of trout. 



D P V A 



Females .. 1-48 .. 1-93 .. ' 2-10 .. 4-86 



Males .. 0-93 .. 0-91 .. 1-44 .. 0-94 



* Study of Fishes, p. 634, 



