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Assessment of Genetic Diversity in Wild and Hatchery Populations of Mrigal Cirrhinus Cirrhosus (hamilton- Buchanan) Using Allozyme Markers

Md. Abul Hasana
Department of Fisheries, Ministry of Fisheries and Livestock, Bangladesh.

Md. Fazlul Awal Mollah
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Md. Samsul Alam
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Abstract/ Executive Summary:

Allozyme markers were applied to elucidate the genetic structure of three rivers (viz. the Halda, the Jamuna and the Padma) and three hatchery (Brahmaputra, Raipur and Sonali) populations of mrigal (Cirrhinus cirrhosus). Electrophoretic analysis of twelve enzymes revealed a total of 20 loci of which four were polymorphic (P₉₅). Compared to the hatchery populations, the average observed and expected heterozygosity were higher and the inbreeding coefficients were lowe r in the river populations. Significant deviations from Hardy-Weinberg expectation were observed in 16.67% cases. The population pair-wise F ST values were low (0.0095-0.0719) to moderate but mostly significant. The number of families and effective population sizes were higher in the river group compared to the hatchery group. Since the level of inbreeding in the hatchery population is high, it is advisable to make periodic renewal of the hatchery broodstocks with fish from relatively better river sources.

Keywords: Genetic variation; Bottleneck; Cirrhinus cirrhosus ; Inbreeding; Population differentiation.

Location: Spawn samples of C. cirrhosus were collected from three rivers namely the Halda, the Jamuna and the Padma and reared in three separate earthen nursery ponds at Bangladesh Agricultural University, Mymensingh.

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Carp fish

Objectives:

To elucidate the genetic structure of three rivers (viz. the Halda, the Jamuna and the Padma) and three hatchery (Brahmaputra, Raipur and Sonali) populations of mrigal (Cirrhinus cirrhosus) .

Methodology:

Spawn samples of C. cirrhosus were collected from three rivers namely the Halda, the Jamuna and the Padma and reared in three separate earthen nursery ponds at Bangladesh Agricultural University, Mymensingh campus until they attained sizes of ~7 cm. For samples of hatchery origin, three hatcheries were selected from three regions of the country. These were Brahmaputra Hatchery (BH) of Mymensingh (Central region), Raipur Government Hatchery (RH), Luxmipur (Eastern region) and Sonali Hatchery (SH), Jessore (South-West region). Fingerlings of approximately same size (~7 cm) were collected in live condition directly from the hatcheries. Muscle tissues collected from each individual were preserved at -20⁰C until used for allozyme electrophoresis. For genotyping fishes at allozyme loci, we used standard horizontal starch gel electrophoresis method as recommended by Shaw and Prasad and described in the NOAA Technical Report. The genotype of individual fish at the allozyme loci was determined and used for estimating genetic variation, population and family structure and differentiation parameters in the populations. Allele frequencies were calculated directly from the observed genotypes. 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. For each population sample, the number of alleles, observed heterozygosity (Ho) and expected heterozygosity (He) were calculated using the software ARLEQUIN version 3.5. The allelic richness and F_IS were estimated using the program FSTAT 2.9.3.2. For comparing heterozygosities observed among the populations, we conducted analysis of variance (ANOVA) test using the softwa re XLSTAT 2013. Conformity to the Hardy-Weinberg expectat ion (HWE) was tested by the exact p values calculated by a Markov chain randomization methods implemented by the software ARLEQUIN 3.5 [18] with the following parameters: forecasted chain length- 1000000; number of dememorization steps-100000). The inbreeding coefficient ( F_IS) within each population at each locus and the population pairwise F_ST values were calculated using the software FSTAT 2.9.3.2. For multiple comparisons, the global significance level of 0.05 was subjected to sequential Bonferroni correction Nei’s genetic distance was estimated using the software GenAlex 6.5 and used for constructing unweighted pair-group method with averages (UPGMA) dendrogram by the software MEGA 5.0. For assigning individuals to the source populations, we applied a direct method of Paetkau et al., and a simulation- exclusion method of Cornuet et al., both implemented by the software GENECLASS 2.0. We reconstructed full-sib families nested within half-sib families using the genotype of 381 offspring collected from six different populations using the software COLONY 1.2. The family reconstruction was performed without accounting for any allelic dropouts and other genotyping errors with the assumption that only one parent, the male, was polygamous. Effective population size (Ne) was estimated by the full likelihood method assuming random mating using the software COLONY 2.0. We examined the evidence for genetic bottlenecks in each population by assessing excess of heterozygosity under the infinite allele model (IAM) using the software BOTTLENECK version 1.2.02.

Source of Information: International Journal of Fisheries and Aquatic Studies 2014; 1(4): 24-31, Retrieve from: http://www.fisheriesjournal.com/archives/2014/vol1issue4/PartA/60.pdf

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In conclusion, we have analyzed different genetic and ecological parameters such as genetic variability, population differentiation and family and effective population size of the Bangladesh stocks of C. cirrhosus , all have important implications for sustainable utilization of genetic resources of this important carp species. We however, recommend using more polymorphic markers such as microsatellite, for fine scale genetic characterization of this species to provide information on genetic variation, population differentiation and effective population size of C. cirrhosus.

Knowledge Management: Journal