Abstract

This study ascertains the morphometric traits and meristic counts of Pomadasys hasta (Bloch 1790) in a mangrove fetched ecosystem (River Arpangasia) from south-west coast Bangladesh. A total of 83 specimens of P. hasta were sampled periodically from the River Arpangasia during July 2020 to June 2021, using cast net and seine net having a mesh size of 1.50-3.00 cm & ~2.50 cm, respectively. A magnifying glass was used to compute the fin rays. Seven distinct morphometric lengths were evaluated and body weight (BW) was measured for each individual. The explored fin formula was: D. XII/11-12; P1. 13-15; P2. I/5; A. iii/8-9; C. 18. Least and highest total length (TL) were 11.65 and 28.00 cm, whereas BWs were 81.60 and 446.34 g, respectively. Entire length-weight relationships (LWRs) were enormously significant (P < 0.001) with r² ≥ 0.949. Off the nine equations, BW = 0.0416*(TL) 2.77 was the most precise model based on the magnitude of r² value. Alongside, considering the r² values, TL vs. SL of length-length relationships (LLRs) was the classical model among eight equations. These data will aid to recognize the species and further assessment of stock/biomass and conservation of P. hasta in mangrove fetched river Arpangasia and other ecosystems of different geographic region.

1. Introduction

The White grunter Pomadasys hasta generally known as "Datina" all over Bangladesh and locally familiar as ''Sada Datina'' (Family: Haemulidae) is captured along with other fishes in coastal brackish and salt waters of Bangladesh. They enter freshwater at depth range 15-115 ¹ hence gripped under ecological group of medium demersal fish ²; occurring at temperatures ranging from 26 to 29°C ³. This fish is important for commercial fisheries ⁴ and are utilized largely for domestic consumption and international trading. More importantly, this species is Threatened in the coastal waters of Bangladesh including mangrove areas ⁵ and under the list of least concern globally ⁶.

Morphometric is an approach employed for describing body shape by measuring the length or gap between physical attributes and peculiarities ⁷. Alternately, meristic is an arena of ichthyology that deals with computing quantitative characteristics of fish such as the number of fins or scales. Furthermore, studies on morphometric and meristic features can be a constructive tools for precise identification of any species and its classification ^{8, 9, 10}. More importantly, in fisheries learning, morphological indices play an enormous role in assessing life history, well-being of individuals and evaluating morphological features of distinct populations ^{11, 12}. As far as the author’s awareness goes, no research have been carried out on the morphometric and meristic features of this fish from Bangladeshˈs territory. However, some endeavors were made on population dynamics, captive breeding, length-weight relationship and biomass distribution of this fish species ^{13, 14, 15, 16}. For this reason, the present investigation had been adopted to elucidate the morphometric traits and meristic characters of P. hasta dwelling in the River Arpangasia, a mangrove dominating coastal river of south-west Bangladesh.

2. Materials and Methods

The study was performed in 3 potential site of River Arpangasia (Latitude: 22°26ʹ N, Longitude: 89°30ʹ E; Latitude: 22°28ʹ N, Longitude: 89°30ʹ E and Latitude: 22°24ʹ N, Longitude: 89°29ʹ) discharging through the landslide of Sundarban mangrove forest located beside Koyra upazila of Khulna district, Bangladesh (Figure 1) during July 2020-June 2021.

Samples of P. hasta (n=83) was collected from fisherman captured with cast net (hauled during low tide) and seine net (hauled during high tide) fortnightly from three different site of Arpangasia river. The fish was identified by using the description provided by Rahman et al. ¹⁷. The collected specimens were immediately cooled in ice and transported to the Fish Biology Laboratory, Brackishwater Station, Bangladesh Fisheries Research Institute (BFRI), Paikgacha Khulna-9280 then stored in 10 % buffered formalin for further study.

The morphometric and meristic traits were investigated following the method stated by Froese and Pauly ¹⁸. The number of fin rays were reckoned by an amplifying glass. Body weight of each specimen was measured with a digital balance to the closest 0.01 g precision. Various linear dimensions viz. total length (TL), standard length (SL), fork length (FL), predorsal length (PrDL) etc. were characterized by measuring board to 0.01 cm accuracy (Figure 2-a). The length-weight relationships were estimated with this equation

Where, W is stand for body weight (g) and L means the various lengths (e.g., TL, SL etc.) in cm.

The regression parameters a and b were calculated by linear regression analysis ²⁸ with natural logarithmic equation: (W) = ln(a) + b ln(L). In addition to this, 95 % confidence limit (CL) of a, b and the coefficient of determination (r²) were enumerated. Moreover, to validate the dissimilarity of b values obtained in the linear regressions a t-test was performed ¹⁹. The best acceptable fitted model for both LWRs and LLRs was ascertained by the highest value of r². All the statistical analyses were performed by using SPSS version 20.0 and Microsoft Excel 2016 tool assigning 5% level of significance.

3. Results

The body shape of P. hasta is ovate, depth 2.5 to 3 times in standard length. Eyes are moderate with diameter 4.0 to 5.0 times of head length. Mouth is small, maxilla reaching below eye and teeth with villi-form band in jaws. Scales ctenoid, rough. Lateral line with 50-52 scales. Dorsal fin with 12 spiny and 11-12 soft rays. Anal fin with 3 spiny and 8-9 soft rays. Second anal spine much harder and longer than third. Juveniles are brilliant silvery with 12 or more faint vertical bars. Adults uniform green above, silvery below (Figure 2-b). The fin formula of P. hasta was: D. XII/11-12; P1. 13-15; P2. I/5; A. iii/8-9; C. 18 (Table 1 and Figure 3) and the TL was varied from 11.65-28.00 cm (mean±SD = 20.43±5.44) and BW was ranged from 81.60-446.34 g (228.07±126.13) (Table 2). The calculated allometric coefficient (b) indicated negative allometric growth (b< 3.00, P< 0.001). The LWRs were highly significant (P< 0.001), with all r² values exceeding 0.949 are presented in Table 3. Moreover, the LLRs (8 relationships) along with the estimated parameters and the coefficient of determination (r²) are presented in Table 4. Also, the calculated LLRs were highly significant (P< 0.001) with r² ≥ 0.908. Table 2 shows the descriptive statistics for length and weight measurements of P. hasta.

4. Discussion

This study provides very first and thorough knowledge on morphometric (LWRs and LLRs) and meristic characteristics of P. hasta from the mangrove fetched River Arpangasia, Southwest coast of Bangladesh. The diagnosed fin formula for P. hasta was dorsal fin, D. XII/11-12; pectoral fin, P1. 13-15; pelvic fin, P2. I/5; anal, A. iii/8-9; and caudal fin, C. 18, which is comparable with the former study of Talwar and Kacker ⁴ in India.

A total of 83 individuals were considered for the current study comprising distinctive body sizes (11.65-28.00 cm). However, during this study, the absence of P. hasta < 11.65 cm TL may be attributed as because of lower market value of tiny fishes the fishers failed to capture the smaller sizes or due to the property of fishing gears ^{20, 21}. The recorded maximum length was 28.00 cm TL which is a conducive tool to calculate the growth parameters, and thereby crucial in planning and management of fisheries resource ²².

In this study, b value (allometric coefficient) was 2.77, which demarking an allometric growth pattern. The power regression parameter b values of LWRs ranging from 2.51 to 2.85 demonstrated negative allometric growth pattern of P. hasta in the River Arpangasia, south-west coast of Bangladesh. Agbugui and Oniye ²³ investigated the morphometric traits of Pomadasys jubelini (Family: Haemulidae) and reported a linear relationship between different parameters. In the linear relationship of present study, only PecL and PelL showed isometric growth to total length, whereas a findings by Kaparis et al. ²⁴ stated that most body components of Pomadsys incisus (Family: Haemulidae) grew isometrically to total length. Generally b values nearest to 3, suggest that fish grow isometrically while those different from 3.0 implies to be allometric growth (>3 positive allometry and <3 negative allometry) ²⁵. However, the value of b may fluctuate within the corresponding species by means of the association of one or more factors, the increase in different parts of the body, the gender, the physiology, the preservation methods and the variance of observed length ranges from the collected samples ²⁶.

Additionally, all LLRs were highly correlated. Interestingly, some meristic characteristics of P. hasta was found closely concomitant with another Grunter species Pomadays maculatus (Bloch 1793) of the same family as reported by Safi et al. ²⁷ in Karachi Coastline, Pakistan. The current study facilitates to the benchmark of biological information, which would be threshold for the development of management strategies for fisheries and conservation of P. hasta population in the River Arpangasia, a mangrove flushed ecosystem and comparative population study of other geographic areas.

5. Conclusion

The knowledge generated of this study will provide adjuvant baseline information of P. hasta populations from south-west coastal river of Bangladesh and could be used in taxonomic, systematic ontogeny and comparative studies with other population of the same species. The morphometric and meristic diversity observed in this study will certainly facilitate in monitoring the species status in the south-west coastal regions of Bangladesh as a bid to take applicable management and conservation measures for the populations in future.

Acknowledgements

We are grateful to the Director General of BFRI for providing financial allocation to carry out this work which is part of the core research project entitled “Cataloging coastal fisheries resources of Bangladesh using DNA barcoding” (Project ID:BFRI/BS/04).

Conflict of Interest

The authors declare that they have no conflict of interest.

Author Contributions

MRW, AKMSAR, and MLI: Together pondered the concept. MRW and AKMSAR: Collected sample and analyzed the data. MRW, and MLI: Wrote, edited and reviewed the manuscript.

References