Abstract

Under northern climatic conditions the occasionally high mortality of the eggs of signal crayfish (Pacifastacus leniusculus) has generally been associated with the low ambient water temperature (0-2°C) during the stocking of berried females prior to artificial incubation. With a simple experiment we tested the hypothesis that higher stocking temperatures would possibly increase the survival of the eggs and thus increase the efficiency and reduce the risks inherent in artificial incubation. The survival of the eggs of noble crayfish (Astacus astacus) and signal crayfish (P. leniusculus) was studied by stocking groups of 25-70 berried females of each species at three different temperatures (0-1°C, 3-4°C, and 5-6°C) for five months prior to artificial incubation of the eggs. The number of eggs and the energy content of the eggs for each berried female was established before and after the experiment and monitoring of mortality was continued until the juveniles hatched and moulted into the 2nd stage. As the highest survival rate of the eggs for both species was found in the group stocked at the highest temperature (5-6°C), we will in this paper discuss the role of the energy content (quality) of the eggs and the physiological condition of the berried females on the survival rates of the eggs and newly hatched juveniles.

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