There are a variety of foods that can be cultured and collected for killifish. Some foods that are collected can not easily be cultured, while others are cultured and seldom if ever collected from the wild. One of the advantages of cultured food is you can "gut load" it with highly nutritions things your fish would never eat. This simulates what fish would be getting in the guts of insects, packed full of phytochemicals we refer to in the trade as "color food": xanthocyanins, carotenes and many others. Insects get them from eating leaves, flowers of pollen and this can be simulated to some extent by feeding micro-particulate (use a blender) beet or carrot.