In this article, sequence analysis of the coding region (5S) and adjacent nontranscribed spacer (NTS) were conducted in red crucian carp (RCC), blunt snout bream (BSB), and their
polyploid offspring. Three monomeric 5S
rDNA classes (designated class I: 203 bp; class II: 340 bp; and class III: 477 bp) of RCC were characterized by distinct NTS types (designated NTS-I, II, and III for the 83, 220, and 357 bp monomers, respectively). In BSB, only one monomeric 5S
rDNA was observed (designated class IV: 188 bp), which was characterized by one NTS type (designated NTS-IV: 68 bp). In the
polyploid offspring, the
tetraploid (4nRB) hybrids partially inherited 5S
rDNA classes from their female parent (RCC); however, they also possessed a unique 5S
rDNA sequence (designated class I-L: 203 bp) with a novel NTS sequence (designated NTS-I-L: 83 bp). The characteristic paternal 5S
rDNA sequences (class IV) were not observed. The 5S
rDNA of
triploid (3nRB) hybrids was completely inherited from the parental species, and generally preserved the parental 5S
rDNA structural organization. These results first revealed the influence of
polyploidy on the organization and evolution of the multigene family of 5S
rDNA of fish, and are also useful in clarifying aspects of vertebrate genome evolution.