Thermal shock induction of triploidy in Atlantic cod (Gadus morhua L.)

Summary

The effects of thermal treatments on induction of triploidy in Atlantic cod have been investigated. Cold shock [-1.7 +/-0.1 1C at 20min post fertilization (PF) for 2 h] was based on a previously developed protocol, and heat shocks, below the lethal threshold of 24C, were at 16,18 or 20C applied 20,30 or 40min PF for 20min. Cold shock did not a¡ect larval survival and was ine¡ective for producing triploids (range 0-4%). A heat shock of 20C at 20min PF generated the highest percentages (range 66-100%) of triploid larvae at hatching, with survival ranging from 10% to 20%relative to the controls. Lower heat shock temperatures or delayed shocks increased survival but decreased the number of triploids, providing no net gain in triploid yield (range 1-9%). Heat shocks applied later than 20min PF produced 2-4% tetraploid larvae at hatching. Athermal shock of 20C initiated at 20min PF and lasting 20min proved to be the most generally efficient treatment for induction of triploidy in Atlantic cod.