Under natural photoperiodic conditions and natural water temperatures, the spermatogenesis and testis cycle of Triturus cristatus cristatus exhibits a clear annual periodicity with one reproductive period extending from the end of April to the middle of June. This cycle can be divided into three different phases:
1 ) progression with expulsion of ripe sperma and subsequent spermatocytogenesis ; 2) regeneration with spermiohistogenesis and maximum testis' weight; 3) gonadal resting phase. An advance of gonadal activity in winter with premature expulsion of mature sperm a was only possible in LD 16 : 8 at 20 ± 1°C water temperature; complete spermatogenesis can occur after the middle of February.
In the winter and summer, water temperature of 11 ± 1°C combined with long days, LD 12 : 12 , or with short days prevent any gonadal activity. Therefore, water temperature of 20 ± 1°C, combined with long days, are a prerequisite for adequate hypothalamus-hypophysis-gonad-activity.
In a year's study with LD 16 : 8 at 20 ± 1°C water temperature, a more or less pronounced spermiahistogenetic activity without expulsion of sperma was observed.