Final answer:
Prophase in Whitefish Blastula is characterized by the dissociation of the nuclear envelope, dispersion of organelles, disappearance of the nucleolus, movement of centrosomes to opposite poles, and the formation of the mitotic spindle. Sister chromatids also coil tightly into visible chromosomes.
Step-by-step explanation:
Prophase is the first phase of mitosis in the whitefish blastula. During prophase, the nuclear envelope starts to dissociate into small vesicles, the membranous organelles fragment and disperse towards the periphery of the cell, and the nucleolus disappears. Additionally, the centrosomes begin to move to opposite poles of the cell and microtubules form the mitotic spindle that pushes the centrosomes apart. Finally, the sister chromatids coil tightly and become visible as chromosomes under a light microscope.