Reduced mitochondrial DNA variation in hatchery populations of ayu ( Plecoglossus altivelis) cultured for multiple generations

Abstract

Ayu ( Plecoglossus altivelis) is a commercially important freshwater fish in Japan. For stock enhancement, release of nonnative stock fry including cultured fish is intensively carried out. We examined the DNA sequence variation in the mitochondrial DNA control region of three wild and six hatchery populations of ayu. Each hatchery population examined had an unique history; although breeding regimes differed between hatcheries, each had persisted for multiple generations without the introduction of any exotic broodstock. Compared to wild populations, hatchery populations showed considerably lower genetic variation and included samples with no variation. Haplotype and nucleotide diversities both decreased with successive hatchery generations, indicating that genetic drift and/or adaptation to culture conditions could be responsible for the reduction in genetic variation. The hatchery populations are considered to have a potential impact on wild populations by reducing the genetic variability through interbreeding.