REARING THE YOUNG FRY. l8l 



fungus growing in the hatching troughs or coming into 

 the water. This can be done by the use of carbonized 

 troughs and aqueducts throughout. 



7. Constitutional weakness. This is an evil which 

 is the necessary lot, we suppose, of a certain propor- 

 tion of all domesticated creatures that are born into 

 the world. This proportion, in the case of domesti- 

 cated trout, can be reduced very much by careful 

 breeding and hatching ; but there is, nevertheless, a 

 limit as with other creatures, beyond which the causes 

 lie too deep and too far back to be controlled. What 

 the limit is with trout is not known. I think Mr. 

 Ainsworth's opinion is, that the percentage of loss from 

 this cause is very large with artificially taken eggs. 

 I think it is much less, and with care in developing 

 strong and healthy embryos need not be over five 

 par cent. The constitutionally weak ones may be 

 distinguished from the rest by being at birth thin, 

 puny, undersized, and looking as if they never would 

 come to anything. There is no help for them, but the 

 number of them can be much reduced by care in the 

 development of the embryo. 



8. Emaciation. Many of the young fry are usually 

 observed to wear away without any visible cause. 

 They do not wholly decline food, but grow thinner 

 and thinner every day, till at last they die. 



This emaciation, although the effect of disease, is 

 classed here among diseases, because the causes are 

 not known. If sufficiently studied, the disorder would 

 probably be found resolvable into some of the other 

 diseases here mentioned. These attenuated fish may 



