If your raising to adults then they will breed on there own so the answer is once.
If planning to feed the mandarin
baby brine ( not for sure that it's enough nutrition though so you will need to research a bit more ) You can hatchem' drain into a brine shrimp net then put them in a peanut butter jar ( or about that size ) with salt water. In the refrigerator the metabolism goes down so they stay nutritious longer, I don't keep them longer than about 3 days in the frig. If your do not refrigerate then need to be used up in 24 hours as they are no longer any nutritional value to them. Can also gut load them after the 24hours with Selco to make more nutritious but only for about 12 hours.
Also, seriously consider decap the brine shrimp. This makes them hatch in about 12 hours as opposed to 24 hours with the shells. Plus alot less messy because you don't have to deal with the shells. Supposedly they are also more nutritious becuase they require less energy to hatch so don't use up as much yolk.
I don't have the link at work that I found to be the easiest directions on decap the eggs but can get it if you need. Process takes about an hour and the decap eggs last in the refrigerator for about 2 months so you decap alot at once.
I use baby brine to raise
Bangaii Cardinal fry so I've got the system down pretty good but have no experience with raising brine to adults.
