Triploid hard clams Mercenaria mercenaria produced by inhibiting polar body I or polar body II

Two types of triploid hard clams Mercenaria mercenaria were produced by inhibiting polar body I ( PB 1) or polar body II ( PB 2) with cytochalasin B. Treatments were applied at 22–23°C, with PB 1 inhibition starting at 4–7 min postfertilization and ending when PB 2 was first observed in control groups, and with PB 2 inhibition starting at 17–23 min postfertilization and ending when 80% of control eggs released PB 2. Triploid induction success was evaluated by chromosome counting in 2–4 cell embryos and by flow cytometry at larval and juvenile stages. PB 2 inhibition produced more triploids (82%–100%) than PB 1 inhibition (71%–83%), although the difference was not significant ( p  ≥   .088). Triploid percentages in PB 1‐ or PB 2‐inhibited groups showed a small but insignificant decline during the first 6 months. At month 3, PB 1 and PB 2 triploids were not different from their within‐group diploids, but significantly larger than control diploids; PB 1 triploids were significantly larger than PB 2 triploids ( p  ≤   .003). At month 6, PB 1 triploids were not different from either within‐group or control‐group diploids, while PB 2 triploids were significant larger than both within‐group and control diploid; PB 1 triploids were smaller than PB 2 triploids. At month 16, PB 1 and PB 2 triploids in one remaining replicate were not different from their within‐group diploids. Overall, this study shows that triploids can be efficiently produced by PB 1 or PB 2 inhibition, and their growth performance relative to diploids is variable depending on age and replicates or parental genotype.