C. Production of fjngerllngs and of adult fish (trout Donda) . 



1. Rearing of trout fry and fingerlings . 



In general, fingerlings are divided into the folloidng four classes: One suimner old 

 fingerlingsj yearlings; 3 to ^ months old June fingerlings of brook trout; September 

 fingerlings of rainbow trout. 



June fingerlings ^nd also September fingerlings are about 3 to 7 centimeters long; 

 one summer old fingerlings from about 5 to 15 centimeters and yearlings (spring yearlings) 

 from about 10 to 20 centimeters. 



The fingerlings are raised by the two methods of: 



(1) Raising them in larger natural ponds without artificial feeding and 

 at a low rate of stock per pond. 



(2) Raising them in smaller ponds, heavily stoticed and feeding them. 



The fry should not be brought into ponds until they are able to eat and to swia 

 (see Fig. 36), since other?ri.se, and from my own experiences, greater losses are sure to 

 occur. To retard the transfer of the brood into the ponds will also adversely affect 

 the later development of the fish. The date for such transfers is practical]^ of no 

 importance. There is no lack of food in trout ponds, not even in winter. Contrary to 

 the findings of others, I have found that water fleas and insect larvae are plentiful 

 just in winter. 



Ability to eat and to swim is best recognized by the attempts of the brood — after 

 the loss of the greater part of their vitelline sacs — to stand up at the bottom, rise 

 to the surface of the incubators and their attempts to swim finely about. This occurs, 

 according to conditions at about 120 to 200 day-degrees after hatching. The vitelline 

 sac is then still present to about l/3 of its size (see Fig. 36). But the fish already 

 require food and if ncne is forthcoming, the later development will be adversely 

 affected, as He in has demonstrated in 1906. 



In both transfer methods the time between stocking the ponds and overhauling them 

 is of importance. In order to avoid an accumulation of brood enemies, the ponds should 

 be overhauled just before stocking them. The same applies also to natural rearing. An 

 inter'/al of 5 days is about the optimal time according to my own sertes of experiments 

 along these lines. This interval is apparently sufficiently long for the producticm of 

 natural food stuffs in the ponds. 



In practice, good results are obtai/ied if the brood has been fed before their trans- 

 fer into the ponds. Such brood is generally stronger, hence better protected against 

 natural enemies, and above all will then have already outgrovm the risky stage of an 

 infection from Lentospora. A further advantage is that brood, fed in the incubators 

 will be already acL^ustomed to feeding when brought into the ponds, as mentioned earlier. 



The first feeding is frequently done in special "nurseries", for example, in boxes 

 swimming in the brook. These boxes have walls of wire mesh or of perforated metal. It 

 may also be done in water current brood boxes. It is simplest to feed in the long- 

 stream apparatus after removing the hatching boxes. Here is the best protection against 

 diseases (as Lentospora cerebralis) and goes, sind the best attention will be possible. 

 Small ponds of about 30 square meters, stocked with 1,000 fry per square meter, are 

 usable if they are free of disease producers. I cannot directly shai^ the view that 

 ponds are preferable to "nursery" boxes for the first feeding. The pretext, that the 

 brood in the pond is better protected against hunger by sudden suspension of feeding, 

 can hardly be tenable in a well managed industry. 



Experiments which I had conducted by the forestry student, Mr. von dem Borne, in 

 the hatchery of the B)erswalde Forestry School have shown similarly to researches of 

 Wilier and his co-workers, that the size of the brood boxes, the stodc density and the 



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