Fertilized fish eggs go through visible stages:
1. Darkening: Within 24 hours, translucent eggs turn faintly orange or beige. White eggs are likely unfertilized.
2. Embryo Visible: Around 24-48 hours, tiny dark dots (developing eyes) appear.
3. Tail Forms: An elongated shadow resembling a tail bud becomes visible.
4. Blood Vessels and Heartbeat: Vessels form on the embryo's exterior and may pulse visibly.
5. Eyes Fully Formed: Eyes turn nearly black within a few days.
6. Hatching: Most eggs hatch between 2 and 5 days, producing round fry with yolk sacs.