I saw this questioned asked and thought it deserved its own thread.
Fry need live foods, at least at first because live foods help the fry learn to eat. They will instinctively grab and gulp moving food whereas dried foods will be left untouched. It is best to have your foods cultured and ready to harvest before even putting your breeders in the tank.
Baby Brine Shrimp
This is by far the most popular fry food among breeders. It is easy to cultivate, easy to harvest, and doesn't have odor issues as some other cultures will. This can be fed from the free swimming stage up to 1-2 months of age.
To culture brine shrimp you must order BBS eggs online. It is vary rare to be able to find them locally. It is best to order eggs that have a 85% or above hatch rate but other hatch rates work just as well, although you may have smaller numbers of BBS. Once you receive your eggs make sure to put them in the refridgerator.
When your ready to culture you will need to set up a hatchery. Most people make DIY hatcheries but you can also buy them offline. To create your own hatchery [ame="http://www.youtube.com/watch?v=Y8sNx9zTOnQ"]check out this youtube video. [/ame]It is fairly cheap and simple to create your own. BBS take 18-24 hours to hatch so most breeders set up two hatcheries 12 hours apart from each other so there is always a fresh batch of BBS ready to feed.
To harvest your BBS simply turn off the air pump and allow the BBS to settle, then use a turkey baster or a straw and suck up the BBS from the bottom of the hatchery. Rinse them with fresh de-chlorinated water and feed them to your fry. They will last about 12 hours from hatching if you keep the air pump running but most people throw them out.
(aka Micros or MW)
Microworms are a small nematode often fed before BBS because they are smaller than BBS. They are easy to feed and culture. Simply purchase a culture and follow the instructions given to you buy the seller. Basically you will take a plastic carton, fill it with a medium (usually oatmeal), and add your culture. Usually you need to give your culture 1-2 weeks to grow before harvesting so it is best to get the culture before hand. Store it in a room temp. dark cabinet.
To harvest simply take a q-tip (or your finger) and swipe some worms from the side of the container and dip it in the tank. Do not dip from the medium. Re-culture the worms every 2-3 weeks and your culture will last forever. You can feed micros solely for the first 1-2 weeks and it can also be feed in conjunction with larger foods for up to a month.
*There is some speculation that feeding MW can cause missing ventrals but this is strictly anecdotal and many breeders feed MW and produce fish with perfectly fine ventrals.
Infusoria is basically bacteria. It is many tiny organisms that grow in plants, etc. You can culture it or you can just add live plants to your spawning tank. To culture infusoria fill a jar with water and add live plants or even hay. Set it in front of a sunny window or a light for a few days and watch as the water begins to get cloudy. *It can take up to a month to get a good culture growing* Re-culture every 2 weeks.
To harvest simply suck some out and add it to the tank. Infusoria is really only good to feed for the first 1-2 weeks.
Additional information provided by pdxBetta..
Infusoria is protists, which can feed on bacteria. Bacteria are typically ~1Ám (0.001mm), and have no nucleus, while protists are much larger and nucleated. Probably the most relevant protist in "infusoria" is paramecium, which is typically ~200Ám (0.2mm), about twice the thickness of an average human hair. You can see paramecium (barely) with a magnifying glass, while bacteria require a high powered microscope.
The relationship between snails and protists is that snails digest bio waste, and protists can eat snail waste as well as bacteria and algae.
My fry live on "infusoria" from elodea and water sprite in the spawning tank for the first few days of free swimming, at which time I begin bbs, vinegar eels, and micro/banana/walter worms... whatever I have going. To see if you have protists, take a drop of water and put it on a piece of glass. Shine a bright light on it and look through a magnifying glass. You should see very tiny white dots zooming around.
Banana worms are similar to micro worms. They are roughly the same size and are cultured and harvested the same way. They don't have the problem with missing ventrals that MW is known for.
Just like BW, Walter worms are cultured and harvested just like MW. They are slightly larger but can still be fed as a first food. (They are a personal favorite of mine).
** I feed all three (MM, BW, and WW) at once because these worms have different nutritional values and some take longer to sink then others which gives optimum chances of the fry eating them**
Vinegar eels are nematodes found naturally in unpasturized vinegar. They are slightly smaller than MW and make an awesome first food because they swim in the water column rather than sinking. They can live in the tank for a few days before dying which helps with water quality (although that is not a reason to neglect water changes). They can be fed for the first two weeks and as long as the fry can see them you can continue feeding them long after 2 weeks.
To culture VE simply get a jar, fill it with water and vinegar and add some apple slices. Order a culture of VE and add them to the jar. It takes VE about a month to really get going unless you order a large culture. Keep in a dark cabinet at room temps.
To harvest simply suck some VE out and filter it through a coffee filter. Rinse with tank water and then dump the eels in the tank. Re-culture once a month.
(aka Grindals or GW)
Grindal worms are related to the earth worm. They make great foods for fry 1 month and older. They can even be fed to adult fish.
To culture select a medium (mine are being cultured using green scrubber sponge), wet it and add your culture to the top. Take a piece of rigid plastic and add some fish food (flakes work well). Wet them and put the plastic fish food side down on top of the culture. Feed daily
To harvest simply lift the plastic and rinse the worms/food off into a container, rinse again until all the dirt/food is gone and all you have left is worms.
Dried Foods/Frozen Foods
You can begin incorporating dried foods into your feeding regime as early as 2 weeks. Do not expect them to be well received but keep at it and eventually the fry will begin to look at it as food.
Great dried foods are:
Hikari First Bites- can be fed as a first food but are usually not eaten
Golden pearls- BBS eggs that are unhatched
De-caps- BBS eggs that have had the shells removed (these may be the same as golden pearls.. I'm not entirely sure).
Chopped frozen blood worms
Frozen mysis shrimp
Frozen brine shrimp
dried brine shrimp
HBH betta bites
Attinson's Betta Pro
Food is only secondary to water quality when it comes to raising fry but it is still important. Feeding lots of food and feeding high quality food will only improve the quality of your fry. Remember.. just as feeding a variety to your adult fish is the best way to ensure health, feeding a variety to your fry will give you nice healthy fry.