REARING THE YOUNG FRY. 1 73 



the business of selling young fry, this thinning out will 

 come naturally in the course -of your sales, and will 

 need no special attention ; but if you do not sell them 

 off, you must take out enough from each box or 

 trough to leave only a safe number together. The 

 number which it is safe to leave in a given space 

 you must learn by experience, as so much depends 

 upon the water supply, the character and temperature 

 of the water, and other circumstances, that the number 

 cannot be set with much definiteness for all places. 

 You need not, however, be afraid to keep two hun- 

 dred to the square foot, if they are shaded, till the first 

 of May. By that time they will be ready for their 

 summer quarters. You will notice that the young 

 fry in the troughs, soon after beginning to feed, will 

 seem to divide into two bodies, one consisting of the 

 larger and stronger ones, at the head of the trough 

 just below the fall, and the other consisting of the 

 smaller and weaker ones settling down towards the 

 outlet screen. 



The division into these two classes will be main- 

 tained with more or less distinctness through the year 

 and afterwards. The cause of the separation is, that 

 some are really weaker and smaller than others, and 

 these will avoid the more violent water and the pres- 

 ence of the larger ones, who would drive them away 

 if they tried to stay with them. This division of the 

 two classes becomes more marked as they get a little 

 older, because the weaker ones are driven back and 

 are obliged to take the food, the water, and the range 

 that is left them by their superiors, who are all the 



