INFLUENCE OF LIGHT AND TEMPERATURE ON REPRODUCTION AND MOLTING FREQUENCY OF THE CRAYFISH, ASTACUS-ASTACUS L

The effects of light and temperature on reproduction and growth in the noble crayfish, A. astacus L., were investigated. In natural habitats reproduction starts in October when the daylength and temperature are decreasing. Moulting takes place during summer in high water temperatures. In the experiments, reproduction and moulting took place under different light conditions: increasing, decreasing, and artificial (constant and light: dark 5:7). The trigger mechanism in the case of reproduction was a decrease in temperature, and in moulting, an increase in temperature. The light regime thus plays a subordinate role. By doubling the yearly temperature cycle on a 1-year basis, two periods of reproduction and moulting resulted. Egg development, which in nature takes up to 9 months, was shortened to 4 months by increasing the temperature. The possibilities of influencing the time of reproduction and egg development could also result in the production of offspring at times when they do not occur naturally.