Shock timing in mitogynogenesis and tetraploidization of the European sea bass Dicentrarchus labrax

A two-step assay was performed under strictly controlled temperature (14±0.2 °C) to obtain mitogynogenetic and tetraploid offspring in the European sea bass (Dicentrarchus labrax L.). The first (probative) series of trials was aimed at adjusting both intensity and timing of the pressure shock to be applied for doubling chromosome set. Larval hatching (LH) (mean 1±1% for gynogenetic double haploids and 3±2% for tetraploids) was achieved only when the pressure shock was applied within 70–90 min after fertilization and the pressure intensity was set at 81–91 (MPa). Lower pressure (70–80 MPa) produced largely variable results and the lowest pressures (<70 MPa) were ineffective. The second series of trials (optimization) was performed to improve the yield in manipulated offspring by recording the time of the first cleavage in a preliminary fertilization test, and timing the application of the pressure shock accordingly. With this manipulation, mitogynogenesis and tetraploidization success rates consistently increased (mean LH 10±6% and 18±12%, respectively), producing live progeny. A significant linear regression was found between the optimal shock application time and the appearance of the first cleavage. The linear regression may be applicable to other fish species.