REARING OF THE YOUNG FRY. I9I 



on the watch for the appearance of disease, and, when 

 he detects its presence, to act promptly on the maxim 

 in the beginning of Seth Green's work on fish culture, 

 " Never put off till to-morrow what you can do to- 

 day." The progress of disease among young trout 

 is often so rapid, and so epidemic in its character, 

 that you cannot be too vigilant in discovering it, or 

 too prompt in suppressing it. I would add, also, 

 that you must not suppose because none of your fry 

 are dying that no disease is in progress, or that dis- 

 ease has just set in when the fish begin to die. On 

 the contrary, in some instances the disease or offend- 

 ing cause may have been at work for weeks before 

 the first fish actually dies from it. Therefore be vigi- 

 lant and prompt in guarding against the first approach 

 of evil. 



23. Paralysis. There is still another disease to 

 which young fry are subject, and I should call it par- 

 alysis if I thought that fish were subject to this dis- 

 order. It attacked one lot, and only one, of my 

 alevin trout. They had been hatched about a month, 

 and the yolk sac was nearly half gone. There were, 

 perhaps, about two thousand in the compartment. 

 Sixty or seventy were attacked. The first time I 

 discovered that anything was wrong was one morning 

 when the water was being agitated with a feather. 

 The well ones immediately headed with all their might 

 against the current as usual, while a few, only fifteen 

 or sixteen at first, were observed to lie perfectly mo- 

 tionless, and to move unresistingly with the current, 

 and finally to collect in a heap in the centre of an 



