Anmerkungen:
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Beschreibung:
The aim of the study was to determine which holding conditions are most propitious in inducing the greatest number of breeders to spawn within an interval of 5 days. The spawning frequency was defined as the proportion of female breeders that spawned within this given interval of 5 days. To assess fertility and egg quality, the data collected were the number of eggs per gram body mass of the female breeders as well as the percentage of hatchlings and swim-up fry. During the first set of trials, the female breeders were kept at a water temperature of 28ʿC until they were acclimatised, before the water temperature was reduced to 22ʿC for a period of 7 days (group I), 14 days (group II) and 28 days (group III). Subsequently the water temperature was returned to the initial 28ʿC for all three groups of female breeders. There were three corresponding control groups whose water temperature was kept constant at 28ʿC. The spawning rates in group II and group III (40% and 31%) were significantly higher than those of the corresponding control groups (13%, 11%). However, the percentage of hatchlings in the control (group II: 74%, group III: 58%) was twice as high as in the test groups II and III ...