Microsatellites revealed no genetic differentiation between hatchery and contemporary wild populations of striped catfish, Pangasianodon hypophthalmus (Sauvage 1878) in Vietnam

doi:10.1016/j.aquaculture.2009.03.017

Aquaculture

Volume 291, Issues 3–4, 16 June 2009, Pages 154-160

https://doi.org/10.1016/j.aquaculture.2009.03.017 Get rights and content

Abstract

Aquaculture of the striped catfish, Pangasianodon hypophthalmus (Sauvage 1878), in Vietnam has become one of the fastest growing primary food production sectors in the world. Although a demand on quantity of fingerlings is currently reached, it is likely that the long term quality of the stocks may be uncertain due to lacking of genetic broodstock management measures. The present study employed five microsatellite loci to investigate levels of genetic variation of the stripped catfish of the current wild stocks as well as of the selected hatcheries in Vietnam. The study included four hatchery populations and two wild populations spawned in 2005 in the Mekong and Bassac Rivers, and one wild population (spawned in 2006) in the Bassac River. The results showed no genetic differentiation among populations as revealed by F_ST and a model-based clustering method. AMOVA also showed no genetic differentiation between pooled wild and pooled hatchery populations while variation within groups was significant. Genetic variation of wild (mean number of alleles per locus, A = 4.80–6.20; allelic richness, A_r = 4.54–5.06; mean effective number of alleles per locus, A_e = 2.86–3.20; observed heterozygosity, H_o = 0.62–0.65; expected heterozygosity, H_e = 0.62–0.64) and hatchery populations (A = 4.60–5.20; A_r = 4.10–4.83; A_e = 2.80–3.11; H_o = 0.61–0.66; H_e = 0.61–0.64) were not statistically different. There were no evidences for recent genetic bottleneck in all populations. Therefore it is implied that the hatchery stocks of striped catfish in Vietnam were founded from sufficient numbers of brooders and current population size is large. The domestication process is in an early stage.

Introduction

Domestication selection whereby genetic changes occur in hatcheries due to natural selection on fitness and reproductive traits under a human-controlled environment (Doyle, 1983), is an unavoidable process that occurs in hatcheries as a result of captive breeding of aquatic animals for generations. It entails genetic changes caused by either selection, reduction of effective population size (number of broodstocks contributing to a succeeding generation, N_e), inbreeding or combinations of these events (Doyle, 1983). Despite limited documentation, most domesticated aquatic animals have showed changes of various traits towards adaptation to captive conditions (Gjedrem, 2005), for example, improved reproductive success of Nile tilapia, Oreochromis niloticus (Osure and Phelps, 2006). Therefore, domestication is essential for good aquaculture stocks. However, deterioration of traits is also observed, e.g. reduction of survival rate and increasing of abnormality rate of Heterobranchus longifilis after four generations of domestication (Agnèsè et al., 1995), and reduction of growth of Nile tilapia after 50 years of domestication (Brummett et al., 2004), if no rigorous broodstock management is applied.

Loss of genetic variation of hatchery stocks is a common phenomenon which has been reported in many species [e.g., turbot, Scophthalmus maximus (Coughlan et al., 1998); common carp, Cyprinus carpio (Kohlmann et al., 2005); Japanese flounder, Paralichthys olivaceus (Sekino et al., 2002); Atlantic salmon, Salmo salar (Skaala et al., 2004); Kuruma prawn, Marsupenaeus japonicus (Luan et al., 2006)]. This is mainly due to a small founder population and ultimately small effective population size (N_e) (Falconer and Mackay, 1996). As such, it is essential that a proper broodstock management plan is implemented in order to ensure successful domestication.

Striped catfish (Pangasianodon hypophthalmus), also sometimes referred to as sutchi catfish, is a strict freshwater migratory species of the family Pangasiidae and native to the Chao Phraya and Mekong river basins (Rainboth, 1996, Robert and Vidthayanon, 1991). The species is also found in the Ayeyawady basin of Myanmar. Aquaculture of this species has been developed in Thailand for more than 30 years and domesticated stock(s) originated from wild stocks in Chao Phraya River have been established. Aquaculture of the striped catfish in Vietnam has reached commercial scale due to the success of artificial propagation of the Vietnamese stocks of striped catfish in 1996's (Trong et al., 2002, Cacot et al., 2002). The striped catfish aquaculture business has become one of the fastest growing primary food production sectors in the world. Approximately 1.2 million tonnes of this species were produced in 2007 and exported to over 100 countries in the world.

Although currently the supply of striped catfish seed in Vietnam is totally dependent on the operations of hatcheries (270 million Pangasiid fry and fingerlings produced annually) (Van Zalinge et al., 2002, Thang, 2006), issues of genetic management of broodstock have not been addressed (Ha et al., 2008). This poses potential risks associate with losing genetic variation and potential inbreeding, which may hamper the domestication process (Schonhuth et al., 2003). Therefore, the information on genetic diversity of these hatchery and wild stocks is urgently required in order to sustain the quality of broodstock.

Hitherto there are a limited number of studies that addresses the questions relating to genetic variability of the striped catfish. So et al. (2006a) revealed no significant population genetic structure based on mitochondrial DNA-RFLP markers. The follow up study using the hyper-variable marker, microsatellite DNA, revealed three genetically sympatric populations with high level of genetic diversity (So et al., 2006b).

The present study aimed at investigating levels of genetic variation of the stripped catfish of the current wild stocks as well as of selected hatchery stocks in Vietnam using microsatellite DNA markers. Implications for management of broodstock will also be discussed.

Section snippets

Sample collection

Fin clip samples of 391 individuals of P. hypophthalmus were collected from brooder populations reared in four hatcheries located in An Giang and Dong Thap Provinces, two wild populations spawned in 2005 in the Mekong and Bassac Rivers, and one wild population (spawned in 2006) in the Bassac River in Vietnam. Sampling was undertaken between June and August, 2006. Details of sampling localities, sample codes and sample sizes are presented in Fig. 1 and Table 1.

Due to problems associated with

Deviation from Hardy–Weinberg equilibrium (HWE) and linkage disequilibrium

Fisher's exact tests for departures of HWE revealed deviation from HWE towards homozygote excess for all seven populations. As such, the data set was checked for the presence of null alleles which existed in all populations. Thus, the genotype frequencies were adjusted according to the suggestion made by MICROCHECKER. After the adjustment, five populations did not conform to HWE (P < 0.05). However, after sequential Bonferroni correction only PhH4 significantly deviated from HWE, despite a

Genetic diversity within striped catfish populations and an implication on N_e

Genetic variation of striped catfish in Vietnam was characterized by low allele diversity compared to the averages for freshwater fish (A = 9.1 ± 6.1 averaged across 13 species, De Woody and Avise, 2000), marine fish (A = 19.9 ± 6.6 averaged across 12 species, De Woody and Avise, 2000) and for striped catfish populations in Cambodian Mekong River (A_r = 7.9–10.4; sample size = 47.0–59.9; So et al., 2006a). However, the observed and expected heterozygosity was moderate; slightly higher than the average for

Conclusion

In conclusion, the genetic variation within populations of both hatchery and wild striped catfish in Vietnam is moderate as revealed by heterozygosity based on microsatellite markers, which thus implied relatively large population size. However, the allelic diversity was relatively low without evidence for genetic bottleneck. No genetic differences were found between hatchery and the wild stocks. As such, the domestication process is thought to be at a very early stage. The hatchery stocks of

Acknowledgements

Financial support was mainly from Thailand Research Fund awarded to Uthairat Na-Nakorn under the Senior Research Scholar Program 2007 through the project RTA 5080013. The technical assistance of Ms. Srijanya Sukmanomon and Ms. Phinyada Sompuech was greatly appreciated. The authors would like to thank the Vietnam Ministry of Education, Dr. Nguyen Anh Tuan, Rector of Can Tho University (CTU), a leader of Higher Education Project at Cantho University for the granting of a Ph.D. scholarship to Hung

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Microsatellites revealed no genetic differentiation between hatchery and contemporary wild populations of striped catfish, Pangasianodon hypophthalmus (Sauvage 1878) in Vietnam

Abstract

Introduction

Section snippets

Sample collection

Deviation from Hardy–Weinberg equilibrium (HWE) and linkage disequilibrium

Genetic diversity within striped catfish populations and an implication on Ne

Conclusion

Acknowledgements

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Aquaculture

Loss of genetic variation in a hatchery stock of cutthroat trout

Trans. Am. Fish. Soc.

Phylogenetic analysis. Models and estimation procedures

Am. J. Hum. Genet.

BOTTLENECK, a program for detecting recent effective population size reductions from allele data frequencies

Microsatellite DNA variation in wild populations and farmed strains of turbot from Ireland and Norway: a preliminary study

J. Fish Biol.

Establishment of national broodstock centres in Vietnam

Microsatellite variation in marine, freshwater and anadromous fishes compared with other animals

J. Fish Biol.

Socioeconomics of disseminating genetically improved Nile tilapia in Asia: an introduction

Aquac. Econ. Manag.

Detecting the number of clusters of individuals using the software structure: a simulation study

Mol. Ecol.

ARLEQUIN version 3.11, an integrated software package for population genetics data analysis

Introduction to Quantitative Genetics

PHYLIP (phylogeny inference package), version 3.6

Detection of reduction in population size using data from microsatellite loci

Mol. Ecol.

Breeding and selection

Selection and Breeding Programs in Aquaculture

A program to estimate and test gene diversities and fixation indices (version 2.9.3)

Introduction to Population Genetics

Microsatellite and mitochondrial DNA polymorphism reveals life-history dependent interbreeding between hatchery and wild brown trout (Salmo trutta L.)

Mol. Ecol.

Genetic diversity within striped catfish populations and an implication on N_e