XXV111 INTRODUCTION. 



but few diseases, probably owing to the uniformity of the 

 temperature in the medium in which they reside. 



As previously stated, the food of a very large proportion 

 of fishes is of an animal nature, and they feed to a great 

 extent indiscriminately upon one another. From their ex- 

 traordinary voracity, their rapid digestion, and the war of 

 extermination they carry on among themselves, the greater 

 and more powerful fishes consuming the smaller and weaker, 

 from the largest to the most diminutive ; add to this, the 

 constant and extensive destruction effected by the numerous 

 sweeping nets of ruthless man, it is even probable that com- 

 paratively but few fishes die a natural death. 



While the concluding sheets of this work were printing, 

 some Edinburgh and London newspapers contained an ac- 

 count by Sir Francis Mackenzie of experiments on breeding- 

 fish artificially ; and as the present edition contains a reprint 

 of Mr. Shaw's experiments on the same subject, under the 

 head of the Salmon, and also a translation of the paper, ori- 

 ginally published at Hanover, by Mr. Jacobs, on his mode of 

 breeding Trout, referred to by Sir Humphrey Davy in his 

 Salmonia, I trust I shall be excused by the author for insert- 

 ing here also the more recent account as it appeared in the 

 Morning Post of Thursday, October 7, 1841, entitled 



" Practical Instructions for the Breeding of Salmon and 

 other Fish artificially. By Sir Francis A. Mackenzie. 



" In the autumn of 1 840, having selected a brook flowing 

 rapidly into the river Ewe, a hollow spot adjoining to it was 

 selected and cleared out, of the following dimensions : 

 Length, twenty-three yards ; breadth, from twelve to eighteen 

 feet ; and all large stones having been removed, the bottom 

 was covered one foot thick with coarse sand and small gravel, 

 the largest stones not exceeding the size of a walnut. A 



