OCR Text |
Show 1882.] BETWEEN SALMON AND TROUT. 753 of the longest outer one. The maxilla extends posteriorly to beneath the posterior third of the eye. The preopercle has a distinctly oblique lower limb, which in this example is less strongly marked than in No. 2, while merely a simple curve exists in Nos. 3 and 4. The central caudal ray is half the length of the longest outer one in examples 1 and 2, but two thirds in Nos. 3 and 4. Respecting the caecal appendages, Nos. 3 and 4 were first immersed in a weak solution of chromic acid, which has hardened them, facilitating their being counted. No. 3 contained 78, and No. 4 had 61 ; the other two were not examined. If hybrids between the Lochleven Trout and a male Salmon show such variations, it demonstrates the inconstancy of the number of these appendages. W e took two Lochleven Trout, each similar in appearance, and about 8 inches in length, which had been bred at Howietoun from eggs and milt of fish inhabiting the stock-ponds, and were consequently one generation removed from Lochleven parentage; in one they were short and 40 in number, in the other rather long and 67. (The preparations are on the table.) Respecting the scales, from 120 to 121 rows descend from the back to the lateral line. In Nos. 1, 3, and 4 there are 13 passing downwards and forwards from the hind edge of the base of the adipose dorsal fin to the lateral line, while in No. 2 there are 12. Colours. These are nearly identical in all four ; from 12 to 13 lateral parr bands pass down the sides, which are also more or less closely sprinkled with small black spots and some few red ones ; there are also black spots on the gill-covers and on the upper surface of the head. A very remarkable feature common to all is that the dorsal fin has its front upper edge white, with a black intramarginal band, and from 11 to 13 black spots on or between the rays. Attention may here be directed to no white upper edging existing on the dorsal fin in any of the Lochleven variety of Trout at Howietoun, such a mode of colour being restricted to the burn-trout variety at that establishment ; and this forms another link in the chain of facts that these two forms are merely varieties of one species. I wish here to record some experiments commenced on November 15th by Sir J. Gibson-Maitland, while I and others were present. About 3000 ova were obtained from Lochleven Trout, and fertilized with the milt of the American Charr, Salmo fontinalis. They were placed in hatching-box No. 108. About 8000 ova of the American Charr were milted from Lochleven Trout, and placed in hatching-box No. 104. About 9000 ova of the American Charr were fertilized with the milt of a Scotch Charr which has been termed Salmo struanensis, and placed in hatching-box No. 115. In Austria, observes Peyrer, the Charr (Salmo salvelinus) is crossed with the Trout; and the young excel the pure breed in many respects. Whether this is partly due to their being sterile, and consequently not going out of season subsequently to the breeding-season, is not mentioned. The life-history of these true hybrids cannot but be interesting; and such in due time will doubtless be forthcoming from Howietoun. 50* |