Control of activity patterns in crowded groups of male noble crayfish Astacus astacus (Crustacea, Astacidea) by light regimes: A way to increase the efficiency of crayfish production?
Abstract Most crayfish species exhibit behavioral traits (solitary lifestyle, high aggressiveness, establishment of social hierarchies) which in intensive aquaculture systems result in low survival due to cannibalism and reduced overall growth. In addition to selective breeding programs, this situation may be improved by identifying culture conditions (e.g., light regimes) which can alleviate the negative impact of specific behavioral patterns on an effective crayfish production. The present experiments demonstrate a pronounced nocturnality of male noble crayfish Astacus astacus. The circadian system seems to be of rather little relevance to the daily pattern of the collective activity in crowded crayfish groups. Parameters of the light regime (the L/D-ratio of 24-h light–dark cycles, light intensity, background illumination during nighttime) were shown to have a crucial and immediate influence on (i) the daily temporal pattern of activity, (ii) the ‘effective density’ (density of individuals which are simultaneously active), and (iii) the overall daily amount of activity. Except for individuals at the verge of molting, activities were restricted to the scotophase, largely independent of the LD-ratio. The effective density was negatively, the overall daily amount of activity positively, correlated with the length of the scotophase. Both parameters decreased significantly under a dim nocturnal background illumination. An optimal combination of high overall daily activity and low effective density was found under a short-day photoperiod of LD 8:16. As in the long run overall daily amount of activity and effective density may be relevant to growth and survival, respectively, manipulations of the light regime are suggested to be a promising approach to improve the efficiency of a commercial crayfish production. The present results may be useful in designing appropriate long-term experiments which actually measure survival and growth. Statement of relevance Light as potential factor to improve production in RASs.