64 WORK IN THE HATCHING-HOUSE. 



one person can be devoted to the trout, I think it unnecessary 

 to refer to them here. The best and simplest is that used at 

 Howietoun in the experimental tanks Nos. 1, 2, 3, and 4, p. 263. 



-a f o" 



FIG. 22 scale f 



Amateur fish-culturists should, as a general rule, turn out their 

 fry ten days before the yolk-sac is absorbed. It is a very common 

 error to suppose fry will not feed until the absorption of the sac. 

 Where they are deficient of vitality this may be so, but when 

 the produce of properly selected breeders, and when the eggs have 

 been so incubated as to induce great vitality in the embryos, and 

 where the alevins had suitable depth of water and sufficient 

 current, they come on the feed before the total absorption of the 

 sac. Nature has, in fact, provided them with a large reserve of 

 food, and, if vigorous, the hinder portion of the sac becomes separ- 

 ated by constriction, and drops off under ordinary circumstances, 

 and it is only where there is an absence of vitality that the sac is 

 totally absorbed. 



The above does not apply tofontinalis, nor to the ova of young 

 trout, or of grilse, and even with the largest salmon if hatched in 

 water of a falling temperature, whereby the period of alevinage is 

 much prolonged, when the whole nutriment contained in the sac 

 becomes necessary to the life of the fish. 



DESPATCHING FRY. 



In the early days of trout-culture fry formed the principal 

 sales ; few cared for the trouble of hatching the ova. The car- 

 riage of yearlings was far too expensive ; clearing-house rates 

 were unknown ; proper preparation not understood ; nothing 

 better than a carboy had been thought of for their transport. 

 The water in which they were conveyed required to be frequently 



