There is first the question of age and size of the male. It is a somewhat common 

 practice to use young and small males for the fertilization of eggs. Scheurinp: has 

 demonstrated that the spermatozoids from 3 to /, years old males are most lively (motile) 

 and retains their motility the longest. Sklower found that the size of eggs is not 

 influenced by the size of the males. From these findings, there seems to be no objections 

 to the common practice referred to above. But I woiild like to call attention to certain 

 disadvantages, pointed out by Thumi. Thumm found that with fish it is also the rule that 

 mating of small, young males with large and older females will produce a predominantly 

 male progeny. Persistent use of small and young males will by and by react upon the sex 

 proportions, the "sexual figure", i.e. the number of males per 100 females. 



Another question is to the effect if the elimination of older trout does not repre- 

 sent "waste of brood stock"? This is the contention of Sklower . These fish certainly 

 produce large eggs, which in turn produce large sized offspring. 



But it is known, on the one hand, that greater losses in eggs occur from older 

 females and on the other hand, we observe over and over again a greater percentage of 

 sterile fish among them. 



Rainbow trout females, v^ich could be stripped 100 percent during the 2nd and 3rd 

 year shoived 64. percent of sterile fish in the i^th year. (Material used in table I5.) 

 A snaller sterility figure is certainly possible under more favorable conditions and by 

 better feeding, but in practice it has been found that spawners are best eliminated 

 after the age of 7 years. Scheuring made the observation that even among males, steril- 

 ity increases, relatively, with age. 



After this discussion of the care and rearing of trout spanners with regard to 

 paratypical factors, and which predetermine from the egg the size and quality of the off- 

 spring — independent of possible hereditary characteristics — I turn now to the subject of 

 "genotypical" factors, i.e. to the subject of planned rational selection for the pro- 

 duction of trout of commercially profitable hereditary characteristics. 



The aim of selection and of selective breeding is to produce a race of highest 

 standards. I understand by "race", in this connection, the definition of the term as 

 given earlier. The progeny shall reproduce hereditary chairacteri sties, i.e. under like 

 conditions of existence. If these conditions differ, the paratypical modifications of 

 hereditary characteristics can be greatly variable (especially "physiological" character- 

 istics, includinggrowth characteristics). This does not impair the "racial fixation". To 

 the contrary'-, the adaptability of the races to special conditions is of commercial value, 

 A lack of adaptability causes severe failures in the transplantation of races. 



But an absolutely perfect adaptability can never be attained. For this reason it 

 is wrong to continually experiment with the introductions of "original forms", so-called, 

 and so often done in the case of rainbow trout. Breeders should abstain from trying to 

 improve their races by attempts to emulate the types of some other localities. In this 

 respect it is worth noting that the recent importations of rainbov; trout from America were 

 a disappointment from the viewpoint of quality (Jaisch), 



It is far better — as Kronacher has pointed out — to develop and to perfect the rac^s 

 through selective breeding of offspring — as in the case of higher animals — from the best 

 and best performing trout, adapted to local conditions and according to the principles as 

 set forth for carp. 



ViTien fishing out ponds it becomes apparent that the fish, that is, the production 

 abilities of fish vary even among trout. It is erroneous to presume that a continuous 

 selection of the largest and most resistant fish for reproduction is superfluous, because 

 planting experiments in the Baltic Sea have shown that the growth ability of trout is 

 actually greater than is made use of in pond fisheries. It is a fact that brook trout 

 planted in the Baltic Sea increased to I5OO grams (3 lbs.) within two years. It follows 

 that the growth ability of the individual trout must be very great. But that is not the 

 only point to be considered. Food assimilation, resistance against disease and pond con- 

 ditions are of no lesser importance. It is to be presumed that the precociously growing 



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