White worms (Enchytraeus albidus) are a fantastic treat for adult killifish, and they are rarely turned down. They are aquatic-disease free, are full of fat and protein and we all know how much fish enjoy them. They can stay alive in water for days as long as it stays cool.
Luckily they are easy to culture in large quantities, requiring very little attention.
Regime The worms and media are kept in polystyrene 'fish boxes', loosely lidded. Each culture is fed and harvested at the same time approximately every 4-5 days. Cultures live outside (well protected from rodents, pets and the elements, maybe a shed, balcony or garage) all year round. Harvests do vary with the seasons, its often the case that no worms are available in the very hottest and very coldest weeks of the year; its best to give the worms a break, as they are not breeding at this time anyway.
The worms are fed under glass 4-5" square, each culture having 3-5 feeding areas. A go. The worms start to consume the food from below and the sides. Harvesting is easy, simply scoop the worms from around the leftover food, or lift the 'food lump' and scoop out more. One culture with 3-4 feeding squares can feed several hundred fish about once/week
Media Culture media does not seem to be critical, a blend of coir (45%), peat/compost (45%), a small amount of sand (10%), maybe a handful of lime if you've got it. Cultures will turn acidic eventually and should either be replaced with new cultures if production drops, or partially replaced continuously (I take a few handfuls of media to a fish auction every now and again, and then top up the old culture). If you do not want to subculture too often, activated carbon can be added to the media.
The media should always be damp, yet never waterlogged or sodden.
Food When you want your fish to breed you fatten them up. The same thing goes for whiteworms. I use dog biscuits and sunflower oil. Its cheap, easy to make and guarantees you handfulls of the fattest worms. Simply boil up a pan of water, add lots of dog biscuits and a serious dash of oil. I can't tell you exact amounts here, but you want to have a thick paste; NOT liquid, but barely solid. It does harden more as it cools. I add probably about 50ml oil / litre of wormfood. I then bag it up and freeze it.
Problems Its said that whiteworms make your fish fat. This is rarely a problem with annual fish with a high metabolism, and they certainly don't when you feed them only once or twice each week.
White worms are related to earthworms, and as such they tend to head under ground as soon as they can (where they will eventually die , and pollute the tank). When not feeding in bare bottomed tanks it best to fed only quantities that the fish will eat immediately. Unfortunately apple snails also love whiteworms and can quickly hoover up the whole feeding.
White worms survive for days in tanks, as long as the water is cool. At around 27 degrees C the worms start to 'straighten out', and die. The fish will no longer touch them and unless you spot it quickly they'll pollute the water.