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Sexual Dimorphism of Canthophrys Gongota (teleostei: Cobitidae) Using Landmark-based Geometric Morphometrics in the Atrai River of Bangladesh

M. M. Akter
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200, Bangladesh

M. G. Azom
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200, Bangladesh

M. S. Reza Sabuz
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200, Bangladesh

M. H. Islam
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200, Bangladesh

M. R. Islam*
Department of Fisheries Biology and Genetics, Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200, Bangladesh

Abstract/ Executive Summary:

Studies on sexual dimorphism of gongota Loach Canthophrys gongota (Local name: Pahari Gutum) was performed capturing them from the Atrai River of Dinajpur district in Bangladesh. Females had light blotches and patches with thick and rounded pectoral and pelvic fins while males having dark blotches and patches with thin and comparatively pointed paired fins. Body size, lengths of the anal fin and distances between the bases of pectoral, pelvic and caudal fins were significantly different (5.62 < F < 11.65, P - 0.05) between the sexes of C. gongota. The expansion factors of mean thin-plate grids and vectors also showed that the head region of males was statistically different from females, whereas abdomen and tail of the females were considerably broader than those of the males. Both PCA (principal component analysis) and DFA (discriminant function analysis) plots showed morphologically little overlapping of landmark points which discriminated the females from the males. These findings are the first records on the sexual dimorphism of this rare species that would be baseline in a future study.

Keywords: Paired ﬁns; Head regions; Landmarks; Gongota loach; Atrai River

Location: Department of Fisheries Biology and Genetics, Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200, Bangladesh

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Fish

Objectives:

An attempt was made to assess the sexual dimorphism of C. gongota with a view to identify their key morphometric traits that will be convenient to separate females from the males.

Methodology:

Study area A total of 128 individuals (64 males and 64 females) of C. gongota were collected directly from fishermen of the Atrai River (25.924° N, 88.724° E) in Dinajpur district located in the northwest region of Bangladesh. Fishermen caught fishes by using fine meshed seine net (15 × 3.5 m², mesh size 4 mm). Fishes were immediately (within 1.5-2.0 h) transported with ice box and carried to the laboratory of the Department of Fisheries Biology and Genetics under Hajee Mohammad Danesh Science and Technology University, Dinajpur, Bangladesh. Identification and measurement of specimens At first, external form and/or ornamentation of the collected specimens were examined to find out any traits as reliable indicators in their body followed by Plongsesthee et al. (2012) with some modifications. Body weight (WB) of each individual was measured with a digital balance (HD-602ND, MEGA, Japan) to the nearest 0.1 g for male and female, respectively. Eight lengths of fins (cm) and their distances between bases (cm) were also taken with a vernier caliper to the nearest 0.1 cm for each fish specimen to determine any dissimilarity between the sexes of C. gongota . Finally, fish samples were dissected to collect their gonads for precision of prediction by visual observation of sexes. After gonad collection, sexes were finally detected by observing their testes and ovary (Esmaeili et al., 2017). Before dissection, photographs of the specimen were taken in order to grasp their main sexual dimorphic characters using geometric morphometric analysis. Individuals that had damaged fins (e.g. dorsal and caudal fins) not considered for imaging and analysis. Digitalization of images and landmarks During photography, each specimen placed in the center of a dissecting pad (32 × 23 cm2) with a left side of its body facing. A total of 64 males and 64 females were taken into consideration for their photographs (4000 × 3000 pixels, 180 dpi) using a digital camera (Canon PowerShot SX510 HS) where fins of each fish were spread out and pinned in place to offer a distinct view of insertion points into their body. For measuring, a ruler was placed against the lower edge of dissecting pad. Twenty-four landmarks (equal to 24 x and 24 y coordinates) were selected to analyze body shape differences between the sexes using landmark-based geometric morphometrics. Pins inserted on each specimen at all landmarks before taking photographs to make sure the accuracy of landmark locations during digitization. Multiple photographs of an individual were taken to check the acquisition of a quality image. After photography, images reviewed to select the best image for each specimen. Landmark clarity, lighting and angle were examined when selecting a photograph. Once chosen, photograph file was renamed with specimen identity number to classify them accurately as their sex (Santos and Quilang, 2012; Reiss and Grothues, 2015). All pooled images were processed for digitization to decide sexual dimorphism where landmarks were digitized using tpsDig2 software (Rohlf, 2006). After opening the images through this software, the ruler was set for measuring distance and then mouse point was set on two landmark points to get correct and reliable measurements. Statistical analysis More or less mature fishes were used to lessen the effects of intra population shape variations because of allometric growth pattern (Dorado et al., 2012). Specimen data put in rows and two-dimensional landmarks (x and y coordinates) along each row for general procrustes alignment (GPA) by rotating and translating to major axis for linear space (Rohlf and Slice, 1990). The resulting procustes distances were used to calculate in Multivariate Analysis of Variance (MANOVA) to observe whether the differences in morphological traits between sexes of C. gongota are significant or not. The analysis of similarity (ANOSIM) is a hypothetical test that was used to evaluate the phenotypic variations between sexes of this loach. The value of ‘R’ was calculated as 4 (rb-rw)/N(N-1), where ‘rb, is the average rank of all distances between groups, ‘rw’ mean rank of all distances within groups and ‘N’ is the total number of sample (Clarke, 1993). The thin-plate spline algorithm was used to calculate the mean body shape between sexes of C. gongota (Bookstein, 1991). Discriminant Function Analysis (DFA)

Source of Information: Bangladesh J. Sci. Ind. Res. 54(2), 187-194, 2019

Article Link (Online Journal): DOI: https://doi.org/10.3329/bjsir.v54i2.41676

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In this study, PCA plots presented that both sexes of this fish population converge or overlapped at low level along the horizontal axis showing higher isolation between the sexes. Discriminant function analysis (DFA) could be a useful method to distinguish different species of the same genus or different stocks of the same species with respect to stock management programs (Karakousis et al., 1991). The overlap and spread of DFA represented 97.66% classification for C. gongota while 58.10%, 64.70% and 44.10 for Cobitis sp., C. faridpaki and C. keyvani, respectively (Mousavi-Sabet and Anvarifar, 2013). Besides, the individuals also grouped into 95.80% for Salmo salar (Solem and Berg, 2011) as different taxa. However, variations between males and females of a ?sh species are important tools for fish stock assessment. The landmark-based geometric morphometric approach enabled us to quantify and visualize morphometric differences between sexes of C. gongota. This finding will be useful to identify sexes of C. gongota species where alteration patterns of sexes can be supportive to both in rearing and culturing with other developmental aspects of this species. Lastly, this landmark-based geometric morphometric study would be a baseline for future study on loaches within and among populations.

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