Whitefish (Coregonus lavaretus L.) larvae from Léman (= Lake Geneva) and Lake Bourget (France) have been successfully mass reared in tanks of 50-60 l when fed exclusively on dry experimental and commercial diets. In spring water at 10 °C for three initial densities (100-200-400/l) tested, the survival at 35 days fluctuated generally between 30 and 50%. The final number and biomass harvested has been improved by the use of higher water temperature (14 °C) or by stocking with high initial density (200-400/l) at 10 °C. In Lake Leman, temperature appeared to be the key factor controlling the results of coregonid larvae rearing in submerged illuminated net cages (6 m3) stocked with 50 000 yolk sac fry and harvested at the end of spring. The results fluctuated greatly when stocking was too early (middle of February to beginning of March). They were improved by delaying stocking, to the period "mid-Marc - carly April" for yolk sac fry or to "end of March-April" when fry prefed on dry diet were used.