196 



SALMONID^ OF BRITAIN. 



Brook Trout.* Plates V, VI, VII, VIII, and X. 



(For synonyimj see page 190 ante.) 



B. x-xii, D. 12-15 (-/_VV), P. 13-15, V. 9, A. 10-12 {^%), C. 19, LI. 110-130, 

 Vert. 56-60. 



Length of headf 4^ to 5yV) in old males has been seen as long as Sa, and 

 as a rale it is always longer in males than it is in females, of caudal fin 7 to 7|, 

 height of body 4 to 5 in the total length. Head much more pointed in some 

 specimens than in others. Much stress, but very unnecessarily so, has been laid 

 upon the form and size of the pieces of the gill-covers. I have, therefore, figured 

 those of two examples from the Windrush, in Gloucestershire, captured on June 

 11th, 1886, and in which the character of these bones was similar on both sides of 



No. 1. No. 2. 



Fig. 43. Gill-covers of brook trout from Windrush, natural 

 size. No. 1, 58 vertebras and 45 casca : No. 2, 57 vertebrae and 

 49 caeca.f 



the head (which is not always the case). In the first (fig. 43, no. 1), the posterior 

 termination of the sub-opercle is obliquely rounded off, but in no. 2 this is much 

 less the case. J Species have even been partially defined by a short lower limb to 

 the preopercle, but it will be seen (see fig. 44, nos. 1 and 2), that this bone becomes 

 comparatively wider in old examples, and thus the length of this limb becomes 

 more or less obliterated. All gradations between these two forms may be found 

 in these fresh-water fishes, consequent upon local peculiarities or age. The com- 

 parative size of the opercle, subopercle, and interopercle, to that of the head, 

 changes very little with age, quite contrary to what is seen in the preopercle. It 

 is necessary to draw attention to the specimens in figure 43, being from trout taken 

 where the southern race is considered to reside, while the ancestors of the New 

 Zealand fish also came from the same area (see p. 183 ante). Eyes — diameter 

 4i to 6 in the length of the head, varying with the size and age of the specimen, 

 li to 2 diameters'from the end of the snout and the same apart. In old breeding 



in most fresh-water forms may be distinct, indistinct, or absent. In the specimens received in 1886, 

 there were distinct finger marks along the sides, and numerous red spots on the body and dorsal 

 fin, and three on the adipose dorsal. Scales — fifteen rows between the posterior edge of the base 

 of the adipose dorsal in a line passing downwards and forwards to the lateral-line. Stomach 

 thickened and similar to the variety termed Gillaroo, in the first lot, but among those received in 

 1886 this organ was not nearly so thickened in a male specimen examined, while in it were tubes 

 of the Ephemerida\ Habitat — respecting its exact residence, Mr. Brooks observed that the upper 

 part of the beck runs over millstone grit, but as it leaves the moor it gets upon mountain lime- 

 stone, and from this point, for a mile and a half, to where it joins the Swale, it is composed of 

 numerous small falls, with intervening little dark pools in which the trout lie. The beck, which 

 is in a narrow ravine, is closely overhung all the way (on the limestone) by trees, mostly alder, 

 silver birch and hazel, but with a good sprinkling of elm, mountain ash, &c. The specimen 

 figured is a male 9 in. long from Swaledale. 



* Salmo irideus from California has been introduced into Britain, the examples at Howietoun 

 seem to indicate that it will develop into a large species, probably the Pacific coast salmon, the 

 " steel-head," Salmo gairdneri. 



f Length of head is subject to great variations : thus in males at 32'5 in. long, I found it 

 5 in. the total length, at 20-7 in. 4§, at 11-4 in. 4|, at 10-5 in. 4§, at 8-8 in. 4|, at 7-3 in. 4i, at 7-2 

 in. 4i, at 7 in. 4^; among /emaZes at 31-5 in. 5^^rrOi the total length, at 19-2 in. 4, at 13-3 in. 4|, at 

 12 in. 4i, at 11-8 in. 4|, at 10-5 in. 4^, at 10-5 in. 4|, at 84 in. 4| ; for a further series of 

 measurements, see under the head of the Lochleven trout. 



\ Colours of these two fish identical, both captured June 11th, 1886 ; flesh, white. 



