In vitro incorporation of FITC-labeled Vtg derived from the bubble-eye goldfish by zebrafish oocytes. (A) Stability of FITC-labeled Vtg in the culture medium. The medium was subjected to SDS-PAGE after 48 h of incubation at 28°C. (B) Ovarian explant at 48 h of culture with FITC-labeled Vtg solution. (C) FITC fluorescence in the explant. (D) Enlargement of the ovary emitting FITC fluorescence. (E) Ovary explant cultured with purified FITC-labeled Vtg. Arrows show ovaries emitting FITC fluorescence. Scale bar = 200 μm.