In zebrafish chimaerism experiments, the cell injection can involve intra-embryonic cell lyses by osmolar effects. Moreover, the donor cells can be injured during manipulation due to osmolar changes into the transplant pipette. Therefore, the present study aimed to assess the effects of manipulation medium osmolarity on embryonic survival and donor cell viability.

In Experiment I, 0.1 μl to 0.15 μl approximately of an isosmolar solution (300 mOsm) was injected into recipient embryos, which were kept at 300 (E1) or 30 mOsm (E2). Survival at day 1 was significantly higher in the E2 group than in E1 (E1: 68% vs E2: 81%, p < 0.05), but after 5 days embryo survival in the E1 group was slightly higher. In Experiment II, donor cells from zebrafish embryos were exposed (or not) to a possible osmolarity change (inner pipette medium: 300 mOsm vs external medium: 30 or 300 mOsm) using two different micropipette outer diameters, 40–50 and 60–70 μm. Cell mechanical damage was detected in the 40–50 μm pipette (p < 0.05), but not by the handling medium osmolarity. Results recommend the use of a 300 mOsm manipulation medium and bore-sized pipettes adjusted as closely as possible to the donor cell size.

With the aim of carrying out chimaerism and somatic cell–midblastula transition (MBT) embryos co-culture experiments in freshwater fish species, we evaluated the effect of osmolarity and composition of two media commonly used in cell fish culture on MBT zebrafish embryos and their further development and survival. To this end, wild zebrafish dechorionated embryos in midblastula stage were cultured for 6 days (Experiment 1: 189 embryos) or 1 h (Experiment 2: 150 embryos) in three different media: Hanks’ 10% (H-10), 35 mOsm; Hanks’ 100% (CH), 315 mOsm; and L-15 with serum (L-15: 315 mOsm). High osmolarity affected the survival rate (6 days: L-15: 45.1% v. CH: 72.34% v. H-10: 100%, P < 0.05; after 6 days: 0% both in L-15 and CH) and slowed their developmental timing. Embryos showed tail deformation (curly) as well as body paralysis at 48 h when they showed tail movements at 28 h. Differences in tail deformation were observed between high-osmolarity groups (CH: 85.10% v. L-15: 98.04%; P < 0.05). In Experiment 2, no effects on survival rate were observed. Teratogenic effects were only observed in L-15 (L-15: 12.98% v. CH: 0%; P< 0.05). Loss of motility was not detected in any group at 48 h. Optimum osmolar condition for cultured cells and also embryonic cells is around 315 mOsm and so, during chimaerism experiments (usually practised at MBT stage), present results indicate that midblastula embryos can acceptably bear the effects caused by 315 mOsm (CH) for 1 h, even though this involves a certain delay in developmental timing.