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Allozyme Variability Analysis in Striped Catfish (pangasianodon Hypophthalmus, SAUvage, 1878) of Some Hatchery Stocks in Bangladesh

A.T.M.Eunus
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

N.Sultana
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

M.S.Reza
Department of Fisheries Technology, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M.G.Q.Khan
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

Striped catfish (Pangasianodon hypophthalmus, locally called Thai pangas) is currently one of the largest intensively cultured fish species in Bangladesh and its fry production largely depends on commercial private hatcheries. In order to assess the genetic structure of hatchery stocks of Thai pangas, four hatchery samples, namely Belal, Bhai-Bhai, Bhai-Bon and Jahangir from Bogra region were collected for allozyme analysis. Five enzymes EST, GPI, LDH, MDH and PGM were studied in CA6.1 buffer system and three enzymes ADH, G3PDH and IDHP were studied in TG-1, using horizontal starch gel electrophoresis. The enzymes were encoded by 11 gene loci: Adh-1*, Est-1*, G3pdh-1*, Gpi-1*, Gpi-2*, Idhp-1*, Ldh-1*, Ldh-2*, Mdh-1*, Mdh-2* and Pgm*. Within these eleven screened loci, Est-1*, G3pdh-1*, Gpi-2* and Pgm* showed heterozygosity in all the populations studied. The mean proportion of polymorphic loci per population was 36.36% for all the populations studied. The mean proportion of heterozygous loci per individual was found to be 13.33% for all populations. The highest variability measured by the mean number of alleles per locus was 1.545 in Bhai-Bon population. Among the four populations the heterozygosity ratio (Ho/He) was the highest (0.636) and the 1- Ho/He value was the lowest (0.364) in Belal population. The co-efficient of gene differentiation (GST) of four hatchery populations of Thai pangas was calculated 0.614 suggesting higher genetic differentiation among populations. The UPGMA dendogram constructed from Nei s (1972) genetic distance revealed that Belal and Bhai-Bon populations having lowest genetic distance (D=0.005) constructed a cluster and they were differentiated from the other cluster formed by Bhai-Bhai and Jahangir population was D=0.01. The studied populations were geographically close to each other but the Belal population showed greater variation. There is a clear indication that the exchange of broodstock or using broods from the same sources might be the reason for the low genetic distance in the populations of the two clusters (D=0.005 and 0.01). Based on Nei s genetic distance criteria, the four studied hatchery populations of Thai pangas may be categorized as local race or population.

Keywords: Heterozygosity, Polymorphism, Allozyme electrophoresis, Genetic conservation

Location: Bogra district

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Pangus

Objectives:

To observe the genetic status of population of Thai pangas to indicate if any genetic variability happened among hatchery populations of Bangladesh.

Methodology:

Fish samples: The fry of Thai pangas, P. hypophthalmus were collected from four different hatcheries i.e., Balal Uddin Hatchery, Bhai Bhai fish farm, Bhai Bhai fish seed plant and Jahangir fish farm, Bogra, Bangladesh. Thirty individuals from each population were caught randomly to collect trunk muscle tissues for allozyme work. The collected muscle tissues were put in small, previously marked air-tight plastic bags and stored in a freezer (-18°C) immediately. This storage system continued until completion of the electrophoretic analysis. Allozyme electrophoresis: In the experiment, horizontal starch gel electrophoresis method was used for allozyme work. The enzymes analyzed, E.C numbers, abbreviation of enzymes, enzyme patterns and tissue type for horizontal starch-gel electrophoresis. After completion of electrophoresis, the gel was sliced horizontally into five or more sections, depending on the thickness of the gel. Loci were numbered consecutively from the anodal to cathodal side. Thus, the most anodal locus was designed. Gene nomenclature was followed. The electrophoretic bands corresponding to multiple alleles at each locus were alphabetically named as *a, *b, *c in the order of detection. Genetic analysis: Allele frequencies were calculated directly from the observed genotypes. The distribution of the observed genotypes was compared with the expected ones, calculated from the Hardy-Weinberg equilibrium using a chi-square ( 2) test. When the most common (major) allele existed in a frequency less than or equal to 0.95 at a given locus, the locus was regarded as polymorphic. The mean proportions of heterozygous loci per individual, mean proportions of polymorphic loci per population and average number of alleles per population were calculated so as to show the extent of genetic variability for each population. Expected (He) and observed heterozygosity (Ho) were also calculated. Coefficient of genetic variation (GST) was also calculated in order to estimate diversity between sample lots. Genetic distance values (D) were calculated from allelic frequencies for all possible pairs of sample lots. The analysis of allozyme data were performed using POPGENE, version 1.32 and G-Stat, version 3.1 and TREEVIEW package computer program. Based on the D-values, dendogram and radial tree were made by the unweighted pair group method using arithmetic average (UPGMA) method.

Source of Information: Int. J. Curr. Res. Aca. Rev. Volume 2 Number 5 (May-2014) pp. 09-19 ISSN: 2347-3215

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The mean proportion of heterozygous loci per individual was found to be 13.33% for all populations. The highest variability measured by the mean number of alleles per locus was 1.545 in Bhai-Bon population. Among the four populations the heterozygosity ratio (Ho/He) was the highest (0.636) and the 1- Ho/He value was the lowest (0.364) in Belal population. The co-efficient of gene differentiation (GST) of four hatchery populations of Thai pangas was calculated 0.614 suggesting higher genetic differentiation among populations. The UPGMA dendogram constructed genetic distance revealed that Belal and Bhai-Bon populations having lowest genetic distance (D=0.005) constructed a cluster and they were differentiated from the other cluster formed by Bhai-Bhai and Jahangir population was D=0.01. The studied populations were geographically close to each other but the Belal population showed greater variation. There is a clear indication that the exchange of broodstock or using broods from the same sources might be the reason for the low genetic distance in the populations of the two clusters (D=0.005 and 0.01). Based on Nei s genetic distance criteria, the four studied hatchery populations of Thai pangas may be categorized as local race or population.

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