Optimal conditions of 6-dimethylaminopurine (6-DMAP) for triploidy induction in the blacklip abalone Haliotis rubra (Leach, 1814) were investigated, targeting inhibition of second polar body (PB2) formation. Two experiments were conducted at a water temperature of 17.5^18.5 1C where factorial combination of (1) four dosages (DSs) of 100, 150, 200 and 250 mM 6-DMAP, four starting times (STs) of 15, 20, 25 and 30 min post fertilization, and two treatment durations (TDs) of 20 and 30 min and (2) three DSs of 50, 100 and 150 mM 6-DMAP, three STs of 15, 20 and 25 min post fertilization, and three TDs of 10, 20 and 30 min, were applied respectively. Day 3 larvae were sampled for triploidy and survival. Percent triploidy was veri¢ed using £ow cytometry (FCM). Results show that optimal inductions that combine both high rates of triploidy and reasonable survival were those treatments commenced 15 or 20 min post fertilization and continued for 20 or 30 min, using 100 mM 6-DMAP. These conditions induced rates of triploidy and relative survival of 80.5^93.3% and 36.5^40.2%, respectively, in the ¢rst experiment, and corresponding rates were 79.1^93.6% and 20.7^43.0% in the second experiment. High percent triploidy were also obtained in a number of treatments using 150 mM 6-DMAP, but with overall survival rates generally lower than those using 100 mM 6-DMAP.
Results
Early cytologyPolar body1and PB2 extrusions were ¢rst observed 9 and 31 min post fertilization, respectively, in the ¢rst experiment, and 8 and 32 min, respectively, in the second experiment.
Experiment 1: triploidy inductionPercent triploidy in day 3 normal larvae ranged from 29.6% to 93.3% over the 32 treatments (Table 1). No Aquaculture Research, 2004 Optimization of triploidy induction in H. rubra W Liu et al.