Abstract

In a laboratory experiment, ten groups with 62 individuals in each of equal sized male and female noble crayfish, Astacus astacus, (mean length 8.2 cm T.L., range 4.6-11.2 cm, sex ratio F:M 1:1.7) in high density, 62 m^-2, were exposed to combinations of the following treatments: food or starvation with a natural light:dark regime or constant light and with intact dactyls or clipped outer part of dactyls. The experiment began in late May and the effects of treatments were observed during the moulting period in July. In the three untreated groups (food, natural light, intact dactyls), survival was 87.1-91.9%, in treated groups survival ranged from 66.1 to 88.7%. Mortality caused by cannibalism was between 1.6 - 8.1% in control groups and ranged between 1.6 - 9.7% in groups with access to food. In starved groups mortality due to cannibalism ranged between 9.7 - 33.9%. The only starved group without significant difference to fed groups was treated with natural light:dark and clipped dactyls. It is concluded that starvation is the most important factor affecting cannibalism and that partial dactylotomy in general does not significantly reduce cannibalism.

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