Abstract

The growth rate, the frequency of moulting, and the moulting interval of three different populations of juvenile Astacus astacus was studied under experimental conditions for 16 months. The experiments took place indoors and the juveniles were raised individually under a light regime of 12D:12L and a temperature of around 20°C for the entire experimental period. The animals were fed· pellets with· a high protein content. From stages 3 to 7 the average number of days between moults increased from about 11 to 21 days respectively. From stage 7 to 10, each moult-cycle period lasted between 40-80 days. The moult period between stages 7 and 8 was much longer than the previous ones while between stages 8 and 10 they were slightly shorter although much longer than the first 7 moult-cycle periods. This suggests an endogenous rhythm in freshwater crustaceans which live in temperate areas with a pronounced winter period. The average increase in carapace length from stage 2 to 3 was 16-19%, from stage 3 to stage 7, 10-14% and from stage 8 to 10, 10-16%. The average total wet weight values increased for each stage was 33-65% but most of the values were around 40%. The average total wet weight values increased from 30-40 mg at stage 2 up to 500-700 mg at stage 1 0 for the various populations. After 16 months the average weights were 1-2 g with a maximum weight of about 4 g and and the average carapace length 17-21 mm with a maximum length of 28 mm.

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