Effects of different thermal treatments during embryonic development on the artificial incubation efficiency of crayfish (Austropotamobius pallipes Lereboullet) eggs. Control of the embryogenetic duration and implications for commercial production

The development and improvement of artificial incubation techniques for fre shwater crayfish eggs and their incorporation into the working schedule of breeding centres is of great interest for commercial production. Factors su ch as the water circulation system, flow rate, thermal treatment, etc., cou ld strongly influence the success of the process. The present study attempt s to test the possible influence of one of these variables, the thermal reg ime, on both the duration of embryonic development and the efficiency rates obtained in the artificial incubation of white-clawed crayfish (Austropota mobius pallipes) eggs. Four different thermal treatments were tested (three of them included a period at low temperature: 4 degrees-5 degrees C). Surv ival rates to juvenile stage 2 were similar in the four cases, ranging betw een 66.7 and 72.7%. We conclude that water cooling (an expensive management procedure) is not necessary in astacid breeding centres provided that egg development takes place at moderately low temperatures (8 degrees-10 degree s C) with a subsequent increase of up to 15 degrees C from the eyed stage. However, the inclusion of periods at low temperature (4 degrees-5 degrees C ) allows the staggered production of juvenile batches throughout a 3-week p eriod without adverse effects on efficiency rates. This could be useful to breeding centres in meeting seasonal market requirements. In our study, egg and juvenile losses (mortality rate: 15-20%) were concentrated during the last phases of embryogenesis, particularly from the eyed stage to juvenile stage 2, during which they amounted to more than 90% of the overall mortali ty which took place during the artificial incubation process.