This is an automatic fish breeding system, the fish spawn in the moss, they lay their eggs on the grid which then gets sucked through the outflow and into the breeder box, ready to be collected.
You have to setup the egg catcher with a little moss in the ring on top of the mesh, connect the airline tube for airflow (normal tube for sponge filters) a 15 mm tube or the 13mm tube you find in the Fluval breeding box size M and that s it. On the edge i made a plug so you can insert some sand or gravel, and water, to help the box to sink.
Nursery box not included,

NB: don't put too much moss

please note these are specially made to order so are exempt from the remorse returns policy