Blackworms replaced the Tubifex worms in the late 20th century. Two producers of California Blackworms exist that supply all of North America. They're not cultured in the sense microworms are but are instead bred in huge ponds.
The best known are African red worms, commonly sold as bait, make an excellent food for larger fish. African nightcrawlers can also be grown but are really too large for anything but large gluttonous fish.
The next size up from Grindal worms they are also easy to culture. The secret is, they prefer it cool (50 - 65). Given soil, a cool environment and regular feeding, they are fairly prolific.
