54 DOMESTICATED TROUT. 



fine fibre of the flannel itself, which has become de- 

 tached from the screens. But it is a better plan to have 

 a special spout or aqueduct for the gravel filter, be- 

 t^ween the filtering tank and the distributing spout, and 

 to have the latter free from gravel, on account of the 

 gravel in it being often an inconvenience. The gravel 

 should be coarse enough to let the water pass through 

 ' it freely, the pieces being of the average size of chest- 

 nuts, or larger. There is usually enough of this coarse 

 "gravel sifted out when the fine gravel is being pre- 

 pared for the hatching troughs. 



If fine gravel is used, it will force the water to flow 

 over it, and thus defeat its purpose. 



HATCHING TROUGHS, OR HATCHING APPARATUS. 



The hatching apparatus is of course the central fea- 

 ture of your whole indoor establishment, the part for 

 which, indeed, all the rest is created. This is the foun- 

 tain-head, from which all the other departments of the 

 fish farm are furnished with stock. Here you intrust, 

 for six months, the whole of your year's increase, and 

 it occupies so responsible a place that no pains should 

 be spared to get it right. Indeed, you cannot overrate 

 the importance of having your hatching apparatus 

 without a fault, especially as a single defect or neglect 

 may cost you your whole stock of young fishes, not 

 merely part, but perhaps the whole. 



MATERIALS. 



Various kinds of material have been used for hatch- 

 ing trout eggs, the principal of which are wood, soap- 



