Zebra Danio Breeding
Zebra danios are one of the easiest species of tropical fish to breed. The trick is to make sure the other danios don't eat the eggs, which they will if this is not a densely planted tank. One common solution is to put the danios in a separate tank that uses marbles as the substrate (the idea being that the eggs fall in between the marbles where the danios won't be able to eat them).
Feed the danios for a week prior with your best quality food (tubifex, bloodworms, etc.). After transferring them to the new tank, leave them for a few hours to lay the eggs, and then transfer them back to the old tank. You will see fry within a couple days if all goes well.