Mmmm, Food...
Bettas love blood worms, black worms, krill, daphnia, brine shrimp, tubifex worms and mosquito larvae. They can be found in freeze-dried, frozen or live forms.
Freeze-dried Foods
Freeze-dried foods have a long shelf life, are inexpensive, and convenient for the owner. What's more, some chain stores feed freeze-dried foods exclusively to bettas due to their cost effectiveness, so new bettas are normally pleased to eat what they are familiar with. Unfortunately, freeze-dried foods have many negative traits. They are notorious for creating constipation and swim bladder problems as they absorb moisture quickly in the gut. Some nutritional value is lost during the freeze-drying process, and in the case of tubifex worms, it is possible for cheaper brands to harbor deadly bacteria. Many hobbyists will not feed freeze-dried foods for these reasons, though with pre-soaking in tank water for 10 minutes, freeze-dried foods are an enjoyable treat for your betta.
Frozen Foods
As for frozen foods, many fish stores have frozen foods available for a reasonable price to the public. They are typically insect-based, which is perfect for bettas, which are insectivorous by nature. Blood worms, brine shrimp, midas shrimp, and other foods are available from a variety of manufacturers, as are mixed-ingredient carnivore diets. These foods are beneficial because they mimic the natural diet more accurately, are extremely rich, highly palatable, and may be fairly inexpensive based on the number of fish you own. However, one must keep in mind that frozen foods are not nutritionally balanced, and unless fed in great variety may lead to deficiencies and excesses that can be harmful to your betta's health. Furthermore, the richness of these foods promotes obesity, particularly in fish kept in colder aquariums with less swimming space. Finally, frozen foods can be a source of deadly bacteria if stored incorrectly, so always look for signs of re-freezing, and dispose of any excess thawed food after each feeding.Live Foods
Most betta fry start out on a diet of live foods, such as baby brine shrimp or vinegar eels. Well, adult bettas can certainly have live foods as well! Blood worms, blackworms, brine shrimp, wingless fruit flies, and other readily available invertebrates can be cultured with relative ease or purchased in some pet stores as a supplementary portion of your betta's diet. These foods have the benefit of also serving as behavioral enrichment, as they encourage the betta's natural predatory behavior. They are also highly nutritious as they have not lost any of their value from protein-degrading processes like freezing, drying, or sterilization. Unfortunately, live foods have a dark side: it is very easy to make bettas ill with contaminated cultures. Blackworms in particular are notorious for causing deadly internal infections, and should only be purchased from a highly reputable source or cultured at home. What's more, live foods can be pricey, either due to the costs of buying and culturing, or the price in pet stores. Because of this, many betta owners choose sterilized frozen foods instead.