Larger fluctuation of gene frequencies among cultured fish populations has been generally explained by the founder and/or bottleneck effect in the process of artificial propagation. However, the experimental support for this explanation in fish has not been reported. To obtain evidence of the fluctuation of gene frequencies due to sampling, sub-populations formed from one guppy population were examined using the loci A AT-1* and PGM-1*. The AAT-1* and PGM-1* gene frequencies of an experimental population composed by 500 individuals, included 200–300 adult fishes, were stable throughtout generations. On the other hand, gene frequencies fluctuated within a wide range among 16 sub-populations, each made from one parent. The expected number of the sub-population in which the allele was fixed or lost nearly coincided witht he observed number. Thus, it was suggested that the large fluctuation of gene frequencies among cultured populations resulted from sampling errors of the parents.