Effects of egg bath and daily removal of dead eggs on hatching success and production of stage 2 juveniles during artificial incubation in noble crayfish (Astacus astacus L.)

The effects of egg bath (iodine-detergent preparation) and daily removal of dead eggs on hatching success and production of juveniles in stage 2 were investigated during a short (sixteen days) artificial incubation (AI) of noble crayfish eggs. At the beginning of AI, eggs were in phase XII (pulsating heart appearance) and were incubated in 18 polyethylene 1 liter jars (100 eggs/jar, egg density 4.5 eggs.cm(-2)). Six different treatments were tested during AI: C: control group without removal of dead eggs and egg bath; R: daily removal of dead eggs without egg bath; R-LB: daily removal of dead eggs, low frequency of egg bath (once every five days); R-FB: daily removal of dead eggs, frequent egg bath (once every three days); LB: without removal of dead eggs, with low frequency of egg bath; FB: without removal of dead eggs, with frequent egg bath. Egg bath was performed by iodine-detergent preparation Jodisol (dose 2 ml.l(-1) and exposition time 2 minutes). Results showed a better hatching rate after removing dead eggs rather than using the egg bath. Three treatments (R; R-LB; R-FB) showed significantly better survival rates in stage 1 (86.3 +/- 5.4%) and 2 (84.2 +/- 5.4%) than control (74.3 +/- 0.9% and 73.3 +/- 0.5%, respectively). Two treatments (LB, FB) showed no statistically different survival rate in stage 1 and 2 (82.5 +/- 5.5 and 80.7 +/- 5.3%, respectively) than the other treatments. After AI, juveniles from all treatments were reared under controlled conditions. At the end of rearing period, juveniles reached a survival rate of 64.1 +/- 0.5% with mean body length of 22.0 +/- 1.6 mm and mean body weight of 266.0 +/- 50.9 mg. Negative effects of AI on growth and survival of juveniles were not evidenced.