v.lth spleen is begun at once. The ponds must be very well planned, somewhat sloped to 

 allow thorough cleansing, and have v/ater flow over the entire extent. Under favorable 

 conditions and with two sortings in the first summer, the number of fish can be increased 

 right in the beginning from about 1,000 to 1,500 fish per square meter. I recommend, 

 however, if possiole to fish out rainbow trout for the fii'st time in September about four 

 montris after stocking and then set in 100 broodlings per square meter. The majority of 

 the fish attain in September, a length of 7 to 11 centimeters. An infection with gyrod- 

 actylus is not now to be feared, as the development of resistant gyrodactylus spores 

 (which inoculate the bottom and infect brood ponds) has not yet taken place. The trout 

 are sufficiently differentiated in growth so it is advisable to grade them. Lastly, in 

 September the v/eather is so cool that fishing out and prolonged grading can be under- 

 taken without injury. 



The sorting and separation of rainbow trout according to size must not be postponed 

 beyond September. The larger fish vdll crowd the smaller ones too vigorously from food 

 and even attack them. Also, the larger fish can now be fed vdth other food (marine fish, 

 meat). The expensive brood feed can then be entirely available to the small fish. 



The losses up to the fishing out amount to about 60 percent on the average; in case 

 of diseases they are much greater, but under favorable conditions — especially by setting 

 out "nurserj'" brood, losses may drop to 20 to 30 percent. 



Fig. 37. Nursing Ponds of a large trout fishery of central 

 German lowlands. The ponds are connected successively in 

 small series by means of overflows. Inlet conduit in fore- 

 ground, outflow ditch in center. 



ith regard to sorting out, Buschkiel has recommended the following classifications: 



Size belo7/ 5 centimeters. 



" I 5 to 7.5 " 



" II 7.5 to 10 " 



" III 10 to 12.5 " 



" IV 12.5 to 15 " 



'I V above 15 " 



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