(above is a super macro photo!)
I use vinegar eels to feed every new betta spawn. They’re smaller than baby brine shrimp and microworms, and unlike microworms, vinegar eels stay swimming around in the water column. They make a great first food for itty bitty fry of many species!
To culture these, add the starter culture to a bottle of apple cider vinegar and cover the top with something breathable, like a piece of paper towel and a rubber band. After a while there will be a ton of vinegar eels! To feed your babies, glug some of the apple cider vinegar into a coffe filter. Let it drain, add some fresh water, and suck it up with a pipette or syringe.