That is exactly what I do with daphnia Millie. I got a sample from a fellow hobbyist a few months ago and put them in a 10 gallon, unheated, unfiltered tank. I keep an air stone running on the tank to create water movement. I feed the tank twice a day with a mixture of soybean flour and brewer's yeast with a little ground up spirulina flake fish food. I have the mix in a shaker that I use to feed. When I want a live food treat, I use a fish net to scoop up as many daphnia as I want and feed them to my fish. The smaller daphnia go right through the net so they are there to grow bigger over the next few days. The full life span of daphnia is only about 35 days so there is no point in trying to keep too many adults going. Every week or two, I drain out about 1/4 of the water and replace it with clean water from one of my fish tanks. The daphnia are very sensitive about water quality so I can't just use dechlorinated tap water for them. When draining, I get both adult and young daphnia so I use a brine shrimp net to strain the water I am removing and I either put them back into the tank or use them as another treat for the fish. I'm sure this could be done on a smaller scale but I need treats for about 12 fish tanks so it takes quite a few daphnia even for one feeding for each.
I also maintain cultures of vinegar eels, microworms, Walter worms and banana worms. None of the worm cultures are really suitable for adult fish but they make a nice food for newborn egg layer fry. Right now I am using them to feed some rainbow cichlid fry and I gave my adult daughter some microworms to feed her severum fry.