REARING THE YOUNG FRY. 1 77 



at first, and then by dozens, then by hundreds, and, 

 unless some remedy is applied, seventy-five per cent 

 will die the next month, and perhaps all ; and many of 

 them — we are still supposing that they have remained 

 in the hatching troughs — will have a little round ulcer 

 just on the top of the skull, which, when pricked, will 

 discharge a thin, watery fluid. This is the stage, I take 

 it, where Green's book says of their dying, that the 

 cause is not known, nor the remedy. I must disagree 

 with him. The cause is known, and the remedy is 

 known also. The cause of this mortality is twofold. 

 In the first place, the food which has been given them 

 has to some extent, however carefully it may have 

 been fed out to them, fallen to the bottom, and has 

 formed a thin layer over the gravel, which has now 

 had time to become putrescent and has fouled the 

 water with its exhalations. 



In the second place, the diet upon which the fish 

 have been kept, although the best known and very nu- 

 tritious, is deficient in some element indispensable to 

 the health of the trout. It is like the experiment of 

 feeding the dog wholly on olive oil, — the most nutri- 

 tious thing in the world, — but which soon brings on 

 an ulcerating disease that kills him in not many weeks. 

 The remedy for both these causes of disease is the free 

 application of common earth, and it is a certam and 

 effective one. 



I was led to this discovery somewhat in this way : 

 I found my young fry dying by thousands, as just 

 described, and those that were left losing their appe- 

 tites and avoiding the current. I felt sure that the 



