Application of hydrostatic pressure shock for retention of the second polar body in sterlet (Acipenser ruthenus)

Abstract

Induced retention of the second polar body (SPBR) is used for production of triploid fish and/or for restoration of diploidy during induced meiotic gynogenesis (MeiG). Using sterlet, Acipenser ruthenus as model species of sturgeon, a protocol was developed for SPBR with hydrostatic pressure shock, commonly found more considerate for treated eggs of teleosts, instead of heat shock conventionally used hitherto. In the first trial, hydrostatic pressure shock of 55 MPa for 3 min duration applied to eggs 18 min post gamete activation gave the highest fertilization rate (62.14 ± 8.90%) and hatching rate (24.59 ± 8.35%) both on Petri dishes and after pilot testing in Zuger jars (78.55%; 45.75%, respectively). Flow cytometric analysis of relative DNA content confirmed 100% triploidy in all sampled prelarvae from shocked eggs. In the second trial comparing the effectiveness of 55 MPa hydrostatic pressure shock for SPBR with conventional 35 °C heat shock for 3 min duration in order to induce triploidy and/or MeiG, pressure – induced triploids exhibited fertilization rate 62.14 ± 8.90% significantly lower than the control group (79.17 ± 7.64%) but indifferent from that in heat -shocked triploids (60.08 ± 4.65%). In MeiG groups, rediploidization with pressure shock or with heat shock did not reveal significant differences in fertilization rate, triploidization with pressure shock provided significantly higher value (46.54 ± 7.47%) than that obtained with heat shock (13.93 ± 3.46%), while similar to the control group (52.71 ± 1.9%). Hatching rates in both MeiG groups did not differ significantly each other but from values in the control group and in the pressure-induced triploids. Flow cytometric analysis of relative DNA content confirmed 100% and 80% triploidy in prelarvae sampled from the pressure- and heat shocked triploids, respectively. Among the MeiG fish, 26 and 25 analyzed prelarvae out of 30 from each the pressure- and heat shock-rediploidized groups were diploid and the remaining prelarvae were haploid. This experiment confirmed the suitability of 55 MPa hydrostatic pressure shock for SPBR in sturgeons.