Abstract
The introduction of Florida bass Micropterus floridanus into Lake Biwa, where largemouth bass M. salmoides from North America had been propagating, was recognized. Isozymes of 194 individuals from four coastal localities in Lake Biwa from 2000 to 2003 were examined for comparison with former samples collected in the 1990s. M. salmoides and M. floridanus were genetically identified with the diagnostically polymorphic loci of AAT-1 , IDHP-1, MDH-1, and SOD. Alleles symbolized M. floridanus frequently appeared at all of the loci among the individuals examined; in general, about half of the total had those alleles. All of the sample lots fitted the Hardy-Weinberg equilibrium for each polymorphic locus, and most of them showed an excess of heterozygotes. Based on the genotypes at the diagnostic loci, most individuals were identified as F2 hybrids, backcross or higher-generation offspring, indicating that the hybridization between M. salmoides and M. floridanus has already progressed considerably in Lake Biwa. Considering the predominance of M. salmoides in Lake Biwa in the 1990s, the present results indicate the possibility that mass introduction of M. floridanus was carried out on a large scale so as to greatly influence the genetic characteristics of the M. salmoides population.
