Effect of vitrification on mitochondrial membrane potential (ΔΨ_m) and mitochondrial distribution in stage III zebrafish ovarian follicles. Follicles were exposed to 5 µM of JC-1 in L-15 medium for 30 min immediately after warming. JC-1 is a sensitive marker for mitochondrial membrane potential ΔΨ_m, it stains mitochondria with low ΔΨ_m in green, while higher polarized mitochondria fluoresce red. First row images show view of the granulosa cells layer of the ovarian follicles. Second row images show view of the ovarian follicles optical section. Control group (A_I and A_II) shows mitochondria with both red and green fluorescence as well as a well-organized distributional arrangement. Vitrified groups (B and C) show loss of structural organization and the absence of fluorescence indicates loss of ΔΨ_m. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)