Experimental studies based on inferential statistics typically require the rearing of many batches of eggs or fish separately, If this is done with conventional fish rearing methods, the need for laboratory space and equipment are normally very high. This may prevent many researchers from experimentally approaching problems in fish genetics or ecology, especially if treatment differences are expected to be small. We have developed and successfully tested a new procedure with Coregonus sp. fry. Eggs were hatched in Petri dishes kept at 6 degreesC. Yolk-sac fry were reared in a hanging bag system at 15 degreesC with continuous water exchange. We estimate that our new fry-rearing method reduces space needs, infrastructure and material costs by a factor of 10 or more, while beings comparable to previously described methods with respect to animal welfare requirements and the experimenter's working time. (C) 2001 Elsevier Science B.V. All rights reserved.