EFFECTS OF STAGE 2 JUVENILE REMOVAL FREQUENCY ON FINAL SURVIVAL RATES IN ARTIFICIAL INCUBATION OF CRAYFISH EGGS (PACIFASTACUS LENIUSCULUS DANA. ASTACIDAE)

In artificial incubation of astacid crayfish eggs, stage 2 juveniles must be removed by hand from incubators and a significant decrease in survival rates has been recorded between hatching (stage 1) and the first moult (stage 2). To reduce these losses, eggs of Pacifastacus leniusculus were incubated at a density of 6.6 cm−2 and different removal frequencies of stage 2 juveniles from the incubators were tested: every 5, 4, 3, and 2 days, daily and only once at the end of incubation. Formaldehyde was used to control growth of fungi. The best final survival rate (88.6%) was obtained when stage 2 juveniles were removed daily from the incubators. There were no significant differences nor between removals every 2 and 3 days (79.6% and 76.5%, respectively) neither between 4 and 5 days (72.6% and 69.8%, respectively). Considering all treatments, final survival rates decreased as juvenile removal was delayed up to only one removal at the end of incubation.