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A Karyological Study of Tenualosa Ilisha (hamilton, 1822) from the Confluence of Padma and Meghna River of Bangladesh

Md. Abu Horayra
Department of Zoology, Faculty of Life and Earth Sciences, Jagannath University, Dhaka-1100, Bangladesh

Md. Arafat Rahman Khan
Department of Zoology, Faculty of Life and Earth Sciences, Jagannath University, Dhaka-1100, Bangladesh

Faria Akbar
Department of Botany, Faculty of Life and Earth Sciences, Jagannath University, Dhaka-1100, Bangladesh

Susmita Saha
Department of Botany, Faculty of Life and Earth Sciences, Jagannath University, Dhaka-1100, Bangladesh

Mehrab Chowdhury
Department of Zoology, Faculty of Life and Earth Sciences, Jagannath University, Dhaka-1100, Bangladesh

Kazi Nahida Begum*
Department of Botany, Faculty of Life and Earth Sciences, Jagannath University, Dhaka-1100, Bangladesh

Abstract/ Executive Summary:

Tenualosa ilisha (Hamilton, 1822), commonly known as Hilsha shad is a valuable and highly acceptable species in terms of their high flavored properties. Hilsha shad has striking morpho-genetical adaptation to heterogeneous habitats across their migratory routes. Cytogenetic analysis demonstrates the changes in chromosomes. But none was focused on the cytogenetic analysis of T. ilisha in Bangladesh. T. ilisha was found to possess 2n = 42 number of chromosomes along with a karyotype formula: 1M + 31m + 8sm + 2st using giemsa staining technique. The results demonstrated ‘diffuse type of interphase nuclei, co-existence of continuous type and interstitial type of prophase chromosomes respectively. No heteromorphic sex chromosomes were determined cytologically. The presence of diverse types of chromosomes based on centromeric position, gradual decrease in total haploid chromosome complement, mean centromeric asymmetry, coefficient of variation of chromosome length and Stebbins’s classification highlighted its asymmetry in karyotype with advance nature. Therefore, the elemental karyological data will offer information for the proper identification, cytotaxonomical classification, expanding productivity and preservation of genetic resources ofT. ilisha.

Keywords: Karyological data, Clupeidae family, Tenualosa ilisha, Padma and Meghna River, Bangladesh

Location: Chandpur, Bangladesh

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Chromosome, Hilsa

Objectives:

The aim of this study was to perform karyotype study of T. ilisha from Padma and Meghna Rivers of Bangladesh for authentic identification characterization and conservation of fish genetic resources of T. ilisha.

Methodology:

Sample collection: Freshly caught T. ilisha were collected with the help of local fishermen using fishing net from Chandpur, the confluence point of the Padma and Meghna Rivers stretched to the Bay of Bengal. Chandpur was selected as a sample collection site due to the abundance and flavorful quality of T. ilisha.

Fish identification: Identification of T. ilisha was done following the taxonomic study of Rahman (2005). During sampling, the sexes could not be recognized phynotypically as the specimens were small in size.

Fish sample preparation: Ten live fish were injected with 0.01% of Colcemid solution (Colcemid™, New York) at the dose of 0.02 mlg-1 body weight of fish. After 30 minutes,the fish were sacrificed followed by collection of kidney cells and preparation of chromosomal suspension using elsewhere published data with slight modification. Firstly, the dissected kidney was kept within a hypotonic solution of 1% sodium citrate for 20 minutes,1 gm of grinded kidney was taken in a falcon tube containing 1ml of hypotonic solution and centrifuged (Centrifuge, China) at 2000 rpm for 10 minutes. The precipitated cells were mixed with 2 ml of Carnoy’s fixative (1 acetic acid: 3 ethanol) and kept for 30 minutes. The fixed precipitated cells were again centrifuged at 2000 rpm for 10 minutes. This process was repeated for three times with an interval of 30 minutes. At the end of centrifugation, 6 ml of modified Carnoy’s fixative (1 acetic acid: 1 ethanol) was mixed properly with the pellet and kept aside in a falcon tube for a while. The pellet was then shaken for few minutes and few drops of it were smeared on clean and dry slides. The slides were heated, air-dried, and dipped into 6% Giemsa solution (Green Lab Chemicals, Bangladesh). Subsequently, the slides were rinsed gently with slow stream water to wash off excess stain and allowed to keep in open air for 30-40 minutes to dry. Again the slides were dipped into the xylene solution for 10-15 minutes. Finally, the prepared slides were observed under Optika electric microscope and mitotic stages (interphases, prophases and metaphases) were photographed with 40XS magnification using the Euromax camera (CMEX- 10, DC 10000C).

Data analysis: A total of 20 to 25 interphase nuclei and prophase chromosome were observed carefully to analyze the nature of heterochromatic in interphase nuclei and prophase chromosomes of T. ilisha and afterwards categorized on the basis of Tanaka's classification (1971). Twenty-five metaphase plates were observed and among them five well scattered somatic metaphases were considered to count chromosome number and preparation of karyotype and haploid idiogram. Karyotype was prepared considering the total length of homologous pair of diploid chromosome where a haploid idiogram was arranged in regard to the decreasing order of chromosome size. The chromosomes were categorized on the basis of centromeric position (Levan et al. 1964). The fundamental arm number (NF) was determined from the karyotype by attributing the value 2 to bi-armed chromosomes (metacentric and submetacentric) and value of 1 to uniarmed chromosomes (sub-telocentric and telocentric).

Statistical analysis: Mean centromeric asymmetry, MCA, coefficient of variation of chromosome length, CVCL (Paszko 2006), and Stebbins’s classification (Stebbins 1971) were evaluated to characterize the karyological relationship in regard to karyotype asymmetry using a computer based software KaryoType_Win_2.

Source of Information: Bangladesh J. Zool. 49 (2): 243-255, 2021 ISSN: 0304-9027 eISSN: 2408-8455

Article Link (Online Journal): DOI: https://doi.org/10.3329/bjz.v49i2.56261

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The karyological data on T. ilisha revealed 2n = 42 number of chromosomes with detailed karyomorphology could play a contributory role in proper identification and classification of T. ilisha and may provide basic cytological information for the enhancement of sustainable productivity of T. ilisha through molecular technologies of breeding.

Knowledge Management: Journal