| Summary: | 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.
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