Shifting the natural spring-summer breeding season of the Australian freshwater crayfish Cherax quadricarinatus into the winter by environmental manipulations

摘要

Ninety sexually mature Cherax quadricarinatus females were exposed to various combinations of photoperiod and temperature for 2 months during the summer. Females were randomly assigned to either "winter" "semi-winter" or "summer" simulation treatments. In the "winter" treatment, crayfish were exposed to a simulated winter photoperiod (gradual decrease from 14L:10D to 10L: 14D, 4 weeks at short day length followed by gradual increase to 14L: 10D) and temperature (gradual decrease from 27 to 15 degreesC, held for 4 weeks, and then gradual increase to 27 degreesC). In the "semi-winter" treatment, crayfish were exposed to a simulated winter photoperiod and a summer temperature (2729 degreesC). In the "summer" treatment, the crayfish were exposed to summer water temperatures and a photoperiod of 14L:10D. Following the 2 months of conditioning, the females were stocked for 7 months in small groups with males under environmental conditions similar to those of the "summer" treatment. All females were individually tagged and molting and spawning events were monitored. Females exposed to "semi-winter" conditioning in the summer, demonstrated a threefold increase in the rate of first spawning during the winter (December-February) compared with the other females. Crayfish breeders can easily implement these findings since shifting the breeding season into the winter only requires shortening of the photoperiod in the summer. The stocking of ponds in the spring with large nursed juveniles that hatched from eggs spawned in the winter, would allow the attainment of market size at the end of the limited growout season in temperate zones.