204 :'IR. A. H. REID 



summer without rain induces congestion of the ovary and 

 of the ova. 



It seems to be an established fact, that the farther the 

 fish liave to travel to their " redds ", the shorter is the 

 time devoted to the operation of spawning and that in 

 the sluggish streams considerably more time is required 

 than in the faster. Unless all the spawners arrive to- 

 gether, there is always the danger of late arrivals dis- 

 turbing and Avrecking the deposits of the earlier. In 

 such a case, too^ there is the probability of the earlier 

 hatched fry harassing the later and smaller. Nature 

 for some reason or other ordains that they shall crowd 

 together in the quietest and shallowest waters w^hile 

 they are very small. . 



The period of incubation depends almost entirely on 

 the temjjerature of the water and varies greatly. At a 

 temperature of 40 degrees Fahr. the ova may be hatched 

 in about 90 to 100 days, but in streams of higher tem- 

 perature the process is accelerated to 30 or 40 days. The 

 advantages of artificial incubation are, that the water 

 temperature can be regulated to overcome tlie natural 

 irregularities, a more perfect fertilization can be secured, 

 there is little or no wastage of ova, and judicious selec- 

 tion of the ova, alevins and fry ensures a hardy stock. 

 By the selection of ova and milt from liealthy spawners 

 the breed can be improved. Deformation of the fry under 

 pressure or abrasion of the ova or alevins by gravel 

 particles in the ^' redds" is excluded in artificial incuba- 

 tion. Under natural conditions it is reckoned that only 

 about 8 per cent, of the ova are fertilized whereas under 

 artificial incubation ver^^ few are missed. Then again 

 after natural incubation alevins herd together, packed 

 against stones in hundreds and are the wholesale vic- 

 tims of every predatory creature that exists. Perhaps 

 their worst enemy is the duck, wild or domesticated; 

 others are wagtails, sandsnip^, kingfishers, eels, crabs 

 and the larger trout. Those that are left to become 



