Brine shrimp hatchery dish

Simple way of hatching brine shrimp - no airline required.

Fill up with salt water just below the top-edge of the removable walls and scatter brine shrimp eggs along the outer perimeter. 

Place in a well lit area - possibly warm (to increase hatching rate) and just wait.

The eggs will either sink in the outer perimeter or float, while the hatched baby brine shrimps will be attracted by the light coming through the hole in the lid and they'll swim towards the center. 

After 24-48h you'll see that most of the hatched bbs will be in the center, right above the scoop. Pull out the scoop and sieve the brine shrimp in a container. You can repeat the process until satisfied and dump the salt water back in the dish.

Bbs are a great food source for fish fry and live-feeding fish, but generally all fish will love them.
 

--------------------------------------------------------------- SUGGESTION----------------------------------------------------------------

I recommend printing in black so the light doesn't penetrate the walls resulting in bbs gathering on one side instead of the center, if you can print the removable walls and the scoop in white or similar, even better. You can alternatively paint it black or ductaping the surfaces.

FOR THOSE WHO HAVE PROBLEMS WITH THE ROUNDED BOTTOM:
 
There is a simplified version with a straight bottom, to access it you have to download the raw files. (STL and not 3MF)
You should also consider calibrating your printer, because it should not have issues printing it if calibrated correctly.