table lists the size of eggs of a stock of uniform rainbow trout, uniform genotypically 

 and paratj-pically. The enumerated groups are comparable among each other since frequently 

 only one factor, i.e^ age or size differs, while all other factors were kept alike (compare 

 groups 1 and 2 and W, 7 and 8 with 5 and 9; 6 with 9 and 10; 2 with 7 and 10). 



The similarity of hereditary characteristics is guaranteed, since the table deals 

 with a small auid isolated stock, whose progeny underwent examinations from year to year. 

 Cnly the fish in groups 7 to 10 were so kept as not to increase from the 3 to the 4 year, 

 i.e, their nutritional conditions were therefore bad. Their eggs, for these reasons were 

 smaller tlian in the previous year, i.e, when the fish were a year younger. 



Table 15. 



Relations of the size of eggs of mature mother fish of rainbow trout 

 (kept under like conditions) to the size and age of the mother fish. 



Mother trout 



Diameter of the 

 eyed eggs. 



No. 



Genealogical relations and 

 state of nutrition. 



No, Age Individual Average Fluctuation 

 Years weight grams 



"lYom young mothers small eggs, from old mothers large eggs". In the case of radnbow 

 trout, at least, this is not so at all. Sklower made his observations upon materisl, 

 ^a.rjix\g in age as well as size and also perhaps in varying stages of nutrition. 



But there are still other factors which determine the size of eggs. Mrsic (according 

 to Neresheimer) for instance found that overripe eggs become reduced in size on account 

 of resorption. Also, the oxygen content of the water in which spawning takes place can 

 later on, seemingly, influence the size of eggs. In my investigations as reported in 

 table 15, these factors have been kept alike. 



It results from all this that for practical purposes the fishbreeder must strive to 

 raise the possibly biggest but not oldest mother fish . By avoiding extremes, the fish- 

 breeder is sure to have large and well performing eggs and without lowering the amount 

 of ef;js obtainable. He will thus also be protected against disorders in later stages of 

 development and which are of common occurrence in brood from very old mother fish. It is 

 for these reasons that 1 recommended earlier rational feeding of spawners, since large 

 sized fish v.dll only then quickly be raised (as in table 15, No. 2), 



There remain still two more questions with regard to size and age of spawners and 

 which are of importance to the breeder. 



104 



