Abstract

On 17 May 1989, when natural photoperiod was 14:21L:9:39D and increasing at the rate of 10 min per week, groups of crayfish were placed into recirculating systems at 31.5°C, 30.0, and 28.5°C and maintained for 22 weeks under the following light regimes: (1) mock-ambient, (increasing at the rate of 30 min per week for 40 days, then decreasing at 30 min per week); (2) decreasing at the rate of 30 min per week without first increasing; (3) constant photoperiod of 4L:20D; (4) constant photoperiod at the initial level (14:21L:9:39D); (5) constant darkness; and (6) constant light. Egg laying began during the lOth or 11th week in all conditions except regime 4, in which laying was delayed to the 15th week. Total mortality of females was 51.2%, almost all deaths being attributable to cannibalism following a molt. Of those that did not die, 43.5% had become ovigerous by the end of the experiment. Animals in the lowest temperature suffered less mortality (35.5%) than those at higher temperatures (60% and 57.8%) and began egg laying sooner (15.7 weeks vs 16.8 and 18.7). More females (59.1%) became ovigerous in total darkness, while constant light gave the lowest percentage of ovigerous females (36.4%). None of the regimes produced markedly accelerated egg laying. Females at the highest temperature were least likely to become ovigerous. Temperatures over 30°C are undesirable for breeding of this species.

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