EGG INCUBATION IN THE NOBLE CRAYFISH (ASTACUS ASTACUS L.): THE EFFECT OF CONTROLLED LABORATORY AND OUTDOOR AMBIENT CONDITION ON HATCHING SUCCESS, GROWTH AND SURVIVAL RATE OF JUVENILES

摘要

The incubation of eggs on pleopods of 13 female noble crayfish was controlled by means of water temperature after CUKERZIS et al. (1978). Out-door incubation of eggs on pleopods of 15 females was monitored at ambient temperature in an earthen storage pond. With controlled incubation of eggs, the duration of incubation period was shortened and earlier hatching resulted in so-called advanced juveniles. They hatched 88 days earlier than those normally hatched during out-door egg incubation. These 88 days prolonged the rearing period of advanced juvenile crayfish in the 1st growing season. When the advanced juvenile crayfish were isolated, there resulted a significantly lower number of stage 2 juveniles per female kept under controlled conditions (47 ± 25.0 individuals of stage 2 juveniles per female) compared to those females placed under out-door conditions (90.1 ± 46.9 individuals of stage 2 juveniles per female). Two females lost all eggs during controlled egg incubation, while no females lost all eggs during out-door egg incubation. After hatching, both groups (advanced and normally hatched juveniles) were provided with identical rearing conditions. Growth and survival rate were checked regularly. The advanced juvenile crayfish always reached significantly higher size in the given period than those normally hatched because they were 88 days older. At the end of rearing period (beginning of October), the advanced juveniles reached 26.0 ± 3.06 mm mean body length and 0.585 ± 0.197 g mean weight. In contrast, normally hatched juveniles reached 21.3 ± 2.25 mm mean body length and 0.305 ± 0.101 g mean weight. Comparing the growth of juveniles at a given age, the advance juveniles showed slower growth rate than those hatched normally. The advanced juveniles at 90 days of age (20.2 ± 1.83 mm mean body length, 0.207 ± 0.058 g mean weight) had significantly slower growth than those hatched normally (21.3 ± 2.25 mm mean body length, 0.305 ± 0.101 g mean weight). Apart from slower growth, the advanced juveniles also had a lower survival rate in the rearing period. In 90 days of age, the advanced juveniles showed 21% less survival rate than the normally hatched juveniles.