Genetic characteristics of Pacific cod populations in Korea based on microsatellite markers

Abstract

Pacific cod (Gadus macrocephalus) is a commercially important species in Korea. However, overfishing in the 1990s caused a strong decline in catch, and in response, artificially cultured juveniles have been released annually to enhance the stocks. Cod fishing has recently increased in Korea, and the variation within the cod population necessitates the study of their genetic characteristics. In this study, we utilized two newly developed and eight previously reported microsatellite markers to examine the genetic characteristics of Pacific cod populations. We compared the genetic diversity and genetic structure of three cod populations from the Korean coasts with three populations from the North Pacific Ocean. Genetic differences were identified in the eastern sea cod population from Korea. These genetic differences included a large number of alleles per locus, a large number of unique alleles, higher frequencies of the most common alleles, and lower gene diversity compared to the other Korean populations. Additionally, the eastern sea cod population was genetically significantly differentiated from the southern and western sea populations in Korea, in which no significant genetic differentiation was detected (F ST = 0.033 and 0.031, respectively, P \ 0.005).

Genetic variation and population structure of the Pacific cod Gadus macrocephalus in Korean waters revealed by mtDNA and msDNA markers

“…This difference reflects the geographic isolation of the Yellow Sea genetic stock, which is not found in any other area. In contrast, Kim et al [5] found a significantly differentiated population structure between eastern and southern coast Pacific cod in Korea based on an analysis using microsatellite DNA (msDNA) markers, but no genetic differentiation between Yellow Sea and southern coast populations was reported. Grant and Ståhl [6] reported that Pacific cod experienced a severe population bottleneck in the North Pacific Ocean, which led to the loss of gene diversity and gene expression.…”

“…Grant and Bowen [25] suggested that either a recent population bottleneck or a founder event involving a single or a few mtDNA lineages could result in marine fish populations with both low haplotype diversity and low nucleotide diversity. A severe bottleneck event during or after the first migration of the ancestral population into the Pacific through the Bering Strait may be responsible for the low genetic variation [5]. Such a historical bottleneck would be severe around Korean coastal waters because these areas are the southern limit of the geographic range of the species.…”

“…Even though Grant et al [4] and Kim et al [5] observed a weak genetic population structure for Pacific cod in Korean waters, two factors that complicate the interpretation of these studies are sampling time and sample design. The study by Grant et al [4] was conducted outside the spawning season when Pacific cod potentially disperse across great distances; consequently, the samples might represent mixtures from distinct spawning groups.…”

“…The study by Grant et al [4] was conducted outside the spawning season when Pacific cod potentially disperse across great distances; consequently, the samples might represent mixtures from distinct spawning groups. In addition, no information on the exact sampling time is available, and the pooling of samples from each location with smaller sample sizes along the eastern coast of Korea could lead to unexpected results [5]. The aim of the study reported here was to investigate the genetic structure of Pacific cod populations in Korean waters to provide genetic information for conservation and stock management of this species using mitochondrial DNA (mtDNA) and msDNA markers.…”

Physical Parameter Measurement and Theoretical Target Strength Estimation of Juvenile Cod (Gadus macrocephalus)

“…It is one of the most important commercial species in several countries, including Korea (Kim et al 2010). Juvenile cod is a prospective recruitment, because they will return to the spawning area after growing up as their instinct in the certain season.…”