The start of sex maturity daring one spawning period depends upon various factors: 



(1) Upon the variety of fish (brovm trout, char are winter spawners, rainbow 

 trout spawn in the spring). 



(2) Upon the hereditarj' traits of the existing race and the characteristics 

 and deviating traits of certain individuals. 



(3) Upon the water temperature and the modus of changing the water j also 

 upon the regional climate and other local conditions (brown trout will 

 come sooner to maturity the sooner lower winter temperatures follow the 

 warm summer days, while rainbow trout mature earlier the warmer the 

 water during winter and spring). 



(ii) Upon the movement of the water. According to Ahrens. free-water fishes 

 mature earlier than pond fishes, 



(5) Upon their state of nutrition. Dnderniourishment retards maturity. 



Perhaps other environmental factors are also of influence, the presence of the 

 opposite sex, for instance. Ahrens claimed that from the ^th year on, the spawning 

 period will occur at earlier dates but my own experiments with the same stock of rain- 

 bow trout (over a period of 3 years) did not confirm this. Table 12 is based upon these 

 experiments. At the same time it explains the rule given in 3, thereby giving a summary 

 on the average water and air temperatures for each year. 



It shows that the spawning period is seemingly retarded when the month, preceding 

 the spawning (in this case February) is too cold. The broodstock used for my investi- 

 gations came frcm eggs, hatched in 1928 in a fishery with spring water supply. The 

 climate there is mild and the fishes had been stripped on the 10th of February. My 

 investigations also did not allow to formulate the rule that either larger and smaller 

 fishes attain maturity at an earlier date. 



Table 12, 

 Dependence of spawning periods (of rainbow trout) upon the temperature. 



101 



