Live feed organisms are essential for the larval stages of many fish species grown in aquaculture, and juvenile fish reared on live feeds often exhibit higher survival and growth than those reared on formulated feed. The terrestrial enchytraeid (white worm), Enchytraeus albidus, has potential as a sustainable source of live feed because it can easily be mass produced, feeds on a wide range of organic waste materials and has high contents of protein and long-chain poly-unsaturated fatty acids. In the present study, we observed the effect of temperature on population growth over five months using soil microcosms. At the outset, each microcosm was supplied with approximately the same number of cocoons. Hatched enchytraeids were given rolled oats ad libitum as feed. We followed the population growth at seven temperatures in the range of 4–25 °C and investigated body composition in order to find optimal temperature for mass production. Results showed that E. albidus has a broad thermal optimum range and displays almost similar biomass production in the range of 15–22 °C with specific growth rates between 6.5 and 6.8%. In this temperature range, protein contents were 40–45%, glycogen contents 20–25% and total fatty acid contents 15–20% of dry weight. The temperature had a highly significant effect on fatty acid composition. In particular, the abundance of omega-3 fatty acids (18:3ω3 and 20:5ω3) was largest at low temperature. For what concerns achievable density of worms in mass cultures, our results surpassed previous results and showed that densities close to 100 g L
−1 substrate are realistic. Maximum production of biomass can likely reach 80 g live worms L
−1 month
−1 at temperatures between 15 and 22 °C.
