TREATMENT OF FRY IX TROUGHS. 399 



The quantity of water sufficient — say for three 

 thousand eggs which do not breathe, is not sufficient for 

 three thousand fish which do breathe ; their Httle pant- 

 ing gills being at work incessantly day and night 

 absorbing oxygen from the water. 



At this time it is most important to keep a daily 

 register of the temperature of the water. For young 

 fish, though very tolerant of cold, are very intolerant to 

 heat. Look also to your supply cistern. For when the 

 spring suns begin to come out, the iron or slate of the 

 cisterns is apt to absorb heat, and send up the tempera- 

 ture of the water used for breeding. This is often an 

 unsuspected cause of mishap. 



Once for all remember, that, when young fish are un- 

 well, the almost only remedy you can give them is 

 cooler water. The water may always be cooled by 

 lumps of ice floated in the top trough. 



You will find that as the young fish get able to swim 

 about, they will all crowd up into the corner of the 

 trough. This is not a healthy state of things ; it may 

 be remedied by causing the water instead of falling into 

 the box in one stream at one end, to pour into it by 

 many jets throughout its whole extent. This may be 

 done either by making a pipe in the shape of a "]" and 

 boring holes in it (as may be seen in the pipe of an 

 ordinary water-cart), or by a zinc or wooden gutter with 

 holes bored in the bottom adapted in size to the stream 

 of water that is required to run through. 



In spite of all that you can do, after a while you will 

 find the young fish will begin to die — this is a sure sign 

 that they are too thick in the trough ; you must' there- 

 fore take out half of them and place them in another 

 trough, 



I cannot go into details, but the only remedy for 



