Shifting the natural
spring–summer breeding season of the Australian freshwater crayfish Cherax
quadricarinatus into the winter by environmental manipulations
I. Karplus, H. Gideon, A. Barki-2003
Aquaculture, 220(1-4): 277-286
Abstract:
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 °C, held for 4 weeks, and then
gradual increase to 27 °C). In the "semi-winter" treatment,
crayfish were exposed to a simulated winter photoperiod and a summer
temperature (27–29 °C). 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.
(Department of Aquaculture, Agricultural Research
Organization, P.O. Box 6, Bet-Dagan 50250, Israel, e-mail: karplus@agri.gov.il)