The permeability to water and cryoprotectants of immature and mature oocytes in the zebrafish (Danio rerio)

To identify a stage feasible for the cryopreservation of zebrafish oocytes, we investigated the permeability to water and cryoprotectants of immature (stage III) and mature (stage V) oocytes. The permeability to water (μm/min/atm) of immature oocytes at 25 °C (0.37) was significantly higher than that of mature oocytes (0.10). The permeability (× 10−3 cm/min) of immature oocytes to ethylene glycol, propylene glycol, and Me2SO (1.49-3.03) at 25 °C was substantially higher than that of mature oocytes ∼0. The permeability of immature oocytes to glycerol was also high (1.75), although the permeability could not be measured in mature oocytes. Immature oocytes would be more suitable than mature oocytes for conservation of the zebrafish.