CONDITIONS AS TO TEMPERATURE. 293 



spawn in the hot months, it proves a comparatively 

 easy matter to hatch and rear them. We have 

 hatched grayling in an ordinary square box, the 

 bottom being formed by a sheet of finely-pierced 

 zinc, the eggs placed upon this without any covering, 

 and the wood lid secured, a rope being then attached 

 to a staple fixed at one end of the box near the 

 bottom, and the box then moored in mid-stream so 

 that the water can flow intermittently through the 

 bottom, which acts so well upon the ova as to vivify 

 and cause it to hatch in a comparatively limited time. 



To vivify salmon and trout ova when impregnated 

 by the milt, the combined influence of running water 

 of a given temperature, and of solar and atmospheric 

 action is required. The fish themselves, it must not 

 be forgotten, often ascend the stream to the very 

 source in order to gain a lower temperature, and the 

 maximum heat of the water should be about 55 to 

 produce a vigorous and healthy brood of fish, as we 

 have already stated. 



Andamorous or migratory fish, it is well known, 

 invariably return to their native river after their 

 marine trip, for breeding purposes, therefore the rearer 

 of these has ultimately the full benefit of his enter- 

 prise ; and if only the water is adapted to the natural 

 requirements and well being of non-migratory fish, 

 they, especially, will locate permanently wherever 

 placed. Considering the many thousands of eggs 

 carried by a female trout, it will be found an easy 

 matter to hatch and rear if our instructions are 

 followed out any quantity of fish. By the older 



