THE NEW ART OF BREEDING FISH. 155 



results similar to those that would be derived by the 

 use of ponds constructed in salmon rivers, or fed by- 

 water directly emanating from them. Both the de- 

 velopment of the fish in ovo and ab ovo depends 

 upon the temperature of the water, and we know 

 that a single frosty night will reduce by many de- 

 grees the temperature of rills and rivulets ; whereas 

 the currents of large rivers are little affected by it. 

 Fry hatched in ponds fed by these hill-streams must 

 be stinted in growth — ^kept in a status quo during 

 many weeks^and they can never arrive at the smolt 

 state in the same period of time as fry produced and 

 bred in the waters of rivers. These latter fry are in 

 their natural element— natural in its temperature 

 and in the food, insects, and so forth, it produces. 

 On the contrary, fry bred in ponds fed by springs or 

 hill-bums, are, as it were, subjected to a different 

 climate, strange and unnatural to them, barren, or 

 nearly so, of insects, and foreign to their innate 

 tastes. Their progress in growth, therefore, cannot 

 equal that of fry bred in favorable localities. When 

 the ponds are perfectly formed and constructed, 

 they should be filled with water, and it should be 

 allowed to run freely into and out of them for a few 

 days previously to depositing the spawn in them. 

 This is necessary, in order that the newly-laid gravel 

 may be washed well, the beds properly seasoned, 

 and all mud or alluvial matter got rid of. The 

 artificial spawning-beds must be reduced as nearly as 

 can be to the condition of the naturally formed ones 



