Laboratory of Population Genetics Informatics, Graduate School of Agricultural Science, Tohoku University, Sendai, Miyagi, 981-8555, Japan
We examined the genetic variation of one wild and eight hatchery populations of ayu Plecoglossus altivelis assessed by the microsatellite DNA polymorphism. All hatchery populations had persisted for a number of generations from F4 to F31. Six out of the eight had propagated without the introduction of any other stock, however, not a few wild individuals had been mixed with each parental stock of the remaining two hatchery populations through their generations. All hatchery populations even in the mixing populations showed lower genetic variation, i.e. the mean number of alleles (A) and average heterozygosity (He), than those of the wild population. Strong significant correlations between the number of successive generations and both indices of genetic variability could be approximated by a negative linear line in He, but by a negative exponential curve in A. This result suggests that A in hatchery populations reduces faster than He during their captive propagation. The significant homozygote excess was also observed at almost all hatchery populations, indicating that inbreeding could be promoted within hatchery populations. All results would be attributed to genetic drift and/or adaptation of the captive stocks to the culture conditions.