154 THE NEW AKT OF BREEDING FISH. 



a layer of gravel one foot thick at the furthest end, 

 and finishing off towards the mouth mth. a layer of 

 gravel eighteen inches in depth. The bottom of 

 the pond will thus become an inclined plane. The 

 ova are to be deposited at the top of the gradient, 

 where you have finished off with a layer of eighteen 

 inches of gravel, in order that they may have the 

 benefit of sharply running water. The lower part 

 of the inclined plane, or the deepest part of the 

 pond, suits best the fry after incubation. The walls 

 that are to secure the ponds must be strongly built 

 of rough stone. No lime must be used in the con- 

 struction of the walls, or of any thing connected 

 ■with the ponds. Every one ought to know the de- 

 structive effects of lime upon fish. To secure the 

 ponds from the entrance of the smallest fish, besides 

 the iron grating already mentioned, there must be 

 another fixed inside it of copper wire closely inter- 

 laced, so closely as to prevent the possibility of the 

 smallest trout passing through the interstices. If a 

 diminutive trout should enter it would devour the 

 fry as soon as they were hatched. Each end of the 

 pond should be secured in the same way. At the 

 end where the pond water runs out there should be, 

 if possible, a fall into the river, which would effectu- 

 ally i revent the ascension to the ponds of any pre- 

 datory fish. Some persons have tried artificial breed- 

 ing in ponds supplied with water from springs and 

 hill-burns, but in such trials no sensible person 

 ought to expect satisfactory results, or, at any rate, 



