DIRECT COMPARISON OF 6 METHODS TO INDUCE TRIPLOIDY IN BIVALVES

Six agents previously reported to induce triploidy in bivalves were co mpared simultaneously on two separate spawns in the blue mussel, Mytil us galloprovincialis. The agents [cytochalasin B (CB: 1 mg/1), heat (H T: 30-degrees-C), calcium (CA: 0.1 M), caffeine (CF: 15 mM), combined calcium and heat (CAHT), and combined caffeine and heat (CFHT)] were a pplied 20 min after sperm addition, so as to suppress polar body II fo rmation, and left for 15 min. Triploidy was estimated by measuring DNA content in cells from trochophore larvae with microfluorometry. In ad dition, polar body counts, pronuclei behavior and early larval develop ment are reported. CA was least efficient (4.7-7.5%) for triploid indu ction. The five other treatments produced on average 86% (CB), 81% (HT , CFHT), 73% (CAHT) and 71% (CF) triploids. The proportion of D-stage larvae at 48 h was reduced by all treatments, being least reduced from CB and most reduced from CAHT. Treatments involving CA and CF resulte d in smaller D-stage larvae at 48 h. In all treatments except CB, the proportion of larvae feeding at 96 h was reduced (58-95%) compared to the control group (100%). CB was the most effective overall in produci ng viable triploid individuals. If regulations inhibit the use of chem icals, heat may be an alternative but viability is reduced.