Two fish swim upwards together
You can spot a mandarinfish by its blue and orange markings. In the evening, a male and a female can swim up side by side. At the top, the female releases eggs and the male releases sperm. When sperm and eggs join, the fertilised eggs can drift away in the water.
A place opens up
On Caribbean reefs, two bluehead wrasses can also swim upwards together to release eggs and sperm. If a male that guards the spawning site disappears, a large female can take its place. In time, her body changes and she can reproduce as a male.
A nest made of algae
Look for the ocellated wrasse in the Mediterranean. The male gathers pieces of algae to build a nest. Females can lay their eggs there, and the male that built the nest stays close to the eggs. While a female lays her eggs, another male may sneak up to the nest.
The mandarinfish dance
At dusk, two mandarinfish swim up together above the reef to release eggs and sperm.
A signal you cannot see
As a female goldfish gets ready to lay eggs, she releases chemicals into the pond. A male can smell them as they spread through the water.
