Mr. J. Blackwall on the Salmon and Bull-trout. 243 



salmon and actually curved outwards in the bull-trout, thus 

 supplying the means of forming a comparative estimate of the 

 ages of both species. 



In accordance with what is here stated, I find that specimens 

 weighing from half a pound to a pound and a half have the 

 caudal fin more or less forked, and the vomer well supplied with 

 teeth except at its posterior part, from which some are lost in- 

 variably. Specimens weighing from two to five pounds have 

 the posterior margin of the caudal fin either moderately forked, 

 nearly straight, or curved outwards, according to their size and 

 species, and usually have from three to seven or eight teeth on 

 the anterior part of the vomer, the number, after making a suitable 

 allowance for differences in condition, being almost always in- 

 versely as the weight ; and individuals of large dimensions con- 

 stantly have the posterior margin of the caudal fin straight or 

 conspicuously curved outwards, and retain one or two teeth 

 only at the anterior extremity of the vomer, or are even without 

 any. 



Young salmon and bull-trout weighing from about half a 

 pound to a pound ascend the river Conway during the month of 

 August in much greater numbers than at any other period of the 

 year, and as many of them are infested with that marine parasite 

 the Caligus curtus of Miiller in various stages of growth, there 

 can be no doubt that they have very recently quitted the salt 

 water. These fish, which from oft-repeated examinations of 

 numerous individuals are found to have the tail forked in a 

 greater or less degree, and uniformly to have lost some teeth 

 from the posterior part of the vomer, though its anterior part is 

 still amply provided with them, I feel thoroughly convinced are 

 identical with smolts of both species which descended the same 

 river in the preceding spring, having then the full complement 

 of teeth on the vomer; for salmon and bull-trout of smaller 

 dimensions do not at any time come up the Conway from the 

 sea, as may be ascertained by actual inspection in calm bright 

 weather, when the water is low and clear and the shoals of fish 

 can be distinctly seen ; and if further proof be required, it is 

 abundantly supplied by the conclusive evidence obtained from 

 the large number of specimens taken annually. It is true that 

 I have occasionally procured salmon and bull-trout in the months 

 of March and April which have weighed six ounces only, but 

 they have always been males which had milted or females which 

 had deposited their ova and were out of condition, or what in 

 Scotland are denominated kelts. 



I shall here introduce to notice a few examples illustrative of 

 the loss in weight which salmon and bull-trout undergo by the 

 act of spawning. 



16* 



