When breeding zebrafish, we first have to sex them. Males tend to have a torpedo shaped body and brighter colors, whereas females are rounder, they have dull colors and they also have this ovipositor that the arrow is pointing towards. We set up breeding pairs the night before crossing them. The crossing cages have a divider dividing the males and females and a grate on the bottom that the embryos can fall through. This prevents the embryos from being eaten by the parents. The following day we will pull the dividers and move them to a lower volume of water and put them at an angle to simulate a slope in their natural environment. This can entice them to breed more so than being on a flat surface. Here are some breeding pairs that are very interested in each other and active. These embryos are falling through the great to the bottom of the cage where we can collect them.