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Article

Morphological and Meristic Feature Studies and Marketing Status of Peregrine Crab Varuna litterata from a Coastal Estuary in Sundarbans Mangrove Forest, Bangladesh

by
Joyanta Bir
1,2,*,
Prianka Paul
3,
Wasim Sabbir
1,
Khirujjaman Sumon
4 and
Rimu Das
5
1
Fisheries and Marine Resource Technology Discipline, School of Life Science, Khulna University, Khulna 9208, Bangladesh
2
CBET+ One Health Research Group, Research Centre for Experimental Marine Biology and Biotechnology (PiE), University of the Basque Country (UPV/EHU), Areatza 47, 48620 Plentzia, Bizkaia, Spain
3
Department of Fisheries and Marine Bioscience, Jashore University of Science and Technology, Jashore 7408, Bangladesh
4
Department of Environmental Studies, Tennessee Technology University, 1 William L Jones Dr, Cookeville, TN 38505, USA
5
Department of Oceanography, Khulna Agricultural University, Khulna 9100, Bangladesh
*
Author to whom correspondence should be addressed.
Hydrobiology 2025, 4(4), 27; https://doi.org/10.3390/hydrobiology4040027
Submission received: 25 July 2025 / Revised: 5 September 2025 / Accepted: 9 October 2025 / Published: 12 October 2025
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Abstract

Varuna litterata is an estuarine crab species widely distributed across the Indo-Pacific region, commonly dwelling in brackish waters, mangrove forests, and tidal estuaries. In Bangladesh, while four Scylla species dominate the commercial crab market, the locally consumed V. litterata remains a biologically overlooked gem of the coastal waters. These crabs are frequently captured as a byproduct during shrimp fry collection from coastal estuaries. In this context, the current study investigates the reproductive biology, morphometric dynamics, and market potential of V. litterata collected from the Pasur River, a coastal mangrove forest-adjacent estuary of southern Bangladesh. A total of 75 individuals were collected from March to April 2023, comprising 35 males and 40 females, resulting in a sex ratio of 1:1.14 (♂:♀), with a predominance of females. A visual observation of ovary development revealed four distinct maturation stages, with Stage IV (fully mature) being the most prevalent (43%), indicating peak reproductive activity during the sampling period. Morphometric analysis revealed that the average carapace width (CW) was 31.2 ± 5.7 mm and 31.9 ± 5.8 mm and the mean carapace length (CL) was 29.3 ± 4.7 mm and 30.1 ± 4.9 mm in males and females, respectively. However, the mean body weight (BW) was 13.1 ± 4.3 g in males and 12.7 ± 3.8 g in female crabs. The dominant CW class ranges from 33 to 33.99 mm (males) and 28.99–29.99 mm (females), appear to be the most vulnerable to fishing pressure. BW-CW and CL-CW relationships demonstrated negative allometric growth, with high correlations in both sexes. Significant sexual dimorphism was observed, with males having larger cheliped dimensions, while females had broader abdomens, likely supporting reproductive functions that are essential to their conservation. The marketing of this crab remains largely informal, yet rising local demand and prices highlight its emerging commercial potential. Therefore, incorporation into aquaculture and coastal fishery development of this crab species could enhance food security, support livelihoods, and contribute to sustainable blue economy initiatives in Bangladesh.

1. Introduction

Bangladesh features diverse ecosystems, encompassing mangrove forests, estuaries, and rivers, coupled with an expansive 710 km coastal line, fostering rich biodiversity and supporting abundant aquatic resources, including various fishes, crustaceans, crabs, and mollusks [1,2,3]. Crabs are the most ecologically and economically pivotal group of crustaceans, constituting a rapidly expanding industry that is crucial for foreign currency earnings in Bangladesh and numerous other tropical and subtropical Indo-Pacific nations, such as India, Vietnam, Philippines, Indonesia, China, Malaysia, and Taiwan [2,4,5]. The soft and delicious nature of crabmeat, coupled with its huge nutritional enrichment, makes crab a globally popular seafood choice among individuals of all age groups [3,4,6,7]. Additionally, crabs play a crucial role in the ecosystem by contributing to nutrient cycling and supporting the livelihoods of local communities engaged in crab harvesting and aquaculture. Hence, the contemporary crab industry holds substantial potential for strengthening food security and sustaining the livelihoods of vulnerable coastal populations in Bangladesh, as well as across Southeast Asia [3,6,7].
There are around 38 crab species from 11 families reported in the marine and freshwater bodies of Bangladesh, among which around 15 crab species are treated as being of low concern and 5 as vulnerable [6,8]. Among the recorded spectrum of crab species, only a small number, primarily belonging to the Scylla genus (S. olivacea, S. serrata, and S. paramamosain), have garnered attention due to their recognized potential, economically lucrative prospects, and elevated demand within the global market [2,4,6]. Beyond the economically important Scylla crabs, numerous other crab species are gaining popularity as a food source in Bangladesh and many parts of coastal south Asia, presenting new economic opportunities for the region [9,10].
The freshwater edible crab, Varuna litterata, locally known as the peregrine crab or chiti kakra, holds ecological significance as a decapod crustacean species within the coastal mangrove rivers of Bangladesh and India [9,10]. These crabs are often captured unintentionally as bycatch during shrimp fry collection, making them a common component of shrimp fisheries. Though they are not the primary target, their presence is surplus for ecological and economic implications [9,10]. They inhabit estuarine and coastal environments, contributing to sediment turnover and serving as both predator and prey in the aquatic food chain [11,12]. This species also helps maintain ecosystem balance by participating in nutrient recycling and supporting local biodiversity [10,11,12]. Understanding their occurrence and abundance can provide insights into bycatch management and the sustainability of coastal fisheries. Locally, they command substantial demand in coastal districts of Bangladesh due to their delectable taste and affordability, serving as a vital source of supplementary protein and lipids in the diet [12,13]. The meat of the peregrine crab is enriched with protein, carbohydrates, lipids, unsaturated fatty acids, and essential vitamins like retinol, ß-carotene, and vitamin C [9,13,14]. Although information is limited, habitat-related variations in the meat quality of V. litterata have been suggested. Furthermore, V. litterata is also a key player in both freshwater and estuarine food webs, making a substantial contribution to the economic activity of coastal regions; it could also be a good indicator species for environmental impact assessment [14,15]. V. litterata, belonging to the Varunidae family, typically resides in shallow subtidal regions, estuaries, mangrove forests, and adjacent freshwater environments, and is occasionally discovered beneath rocks or within burrows along embankments in shallow riverbanks [9,14,16]. It serves a crucial ecological role in nutrient recycling within freshwater and mangrove ecosystems and acts as a major prey item for numerous predators, thereby integrating into aquatic food webs [16,17].
Typically, these crabs are harvested from natural habitats, mainly mangrove rivers, without proper monitoring of stocks, leading to a rapid decline in the population of this species and placing the stock under an imminent threat from the perspective of conservation [5,10,18]. Most often, fishermen capture these specimens incidentally in their nets when targeting other aquatic species during fishing, thereby classifying them as bycatch [10]. Until recent years, V. litterata was seldom consumed, and fishermen routinely released these crabs back into the river upon capture. However, with a rising demand for these crabs within coastal communities, fishermen now actively target them as additional catch, posing a potential risk to the species’ sustainability [1,14,16]. Very few studies have been conducted regarding the biology of this crab species from the Indo-Pacific area [13,18,19]. However, a comprehensive examination of the biological parameters including the morphometric and meristic characteristics of this crab species is yet to be conducted, hindering the development of effective management strategies for its conservation, highlighting the need for further research, particularly in the realms of stock assessment and examining this species under cultural conditions.
In this context, this paper aimed to study the biological characteristics of the ecologically important crab species V. litterata. To achieve this, we analyzed growth parameters, morphometric, and meristic traits from crab specimen collected from the mangrove-adjacent coastal areas of the Pasur River. Additionally, we visually examined different stages of gonadal development, with the overarching objective of contributing to reproductive biology and the sustainable management of this species.

2. Materials and Methods

2.1. Ethical Statement

All animal experiments were conducted in accordance with the guidelines and regulations of the Biosafety and Ethics Committee at the Khulna University Research and Innovation Center, Khulna University, Bangladesh. (Approval code: KUAEC-FMRT/09/2023). Specimens were obtained with the cooperation of local fishermen and with their informed consent for research purposes.

2.2. Species and Study Location

A total of 75 specimens of Varuna litterata were collected at intervals of every fifteen days during March and April 2023, from shrimp fry collection boats of local fishermen in the Pasur River (Figure 1). Crab specimens were captured as bycatch of shrimp fry by using modified beg nets (a special type of nylon net used for fry collection). The Pasur River, a key coastal river in the Sundarbans mangrove forest connecting directly to the Bay of Bengal, hosts the studied crab species seasonally. The sampling stations were selected manually based on their proximity to human habitation, shrimp fry collection area, and port areas, where water levels regularly fluctuate with the tides (Figure 1). The relatively low sample size was due to the availability of specimens in the studies estuary during the sampling period and to compromise with the ecological disturbance that cause the conservation issues.

2.3. Sex Identification, Sex Ratio, and Gonad Maturation Analysis

The sex of each crab was determined visually by examining the morphology and shape of its abdomen. Males typically exhibited a narrower, V-shaped abdomen, whereas females had a broader, U-shaped abdominal flap (Figure 2). The gonad maturation stages of crabs were visually assessed by observing gonadal development according to Ikhwanuddin et al. [20]. The sex ratio of the collected crab samples was estimated by the following formula.
Sex ratio = (total number of female)/(total number of male) × 100

2.4. Measurement of Morphometric Parameter of Crabs

Morphological and meristic data of the crab specimen were collected in situ from a fishing boat during the sample collection period from fishermen, using standard measurement tools to record physical characteristics. Crab body weights (BW) were precisely measured in grams, using a digital balance (Mode:EK600i, A&D Company, Seoul, Republic of Korea) with a sensitivity of 0.1 g, while key morphometric measurements were obtained using vernier calipers (Suzhou Tolsen Tools Co. Ltd., Zhangjiagang, China) with an accuracy of 0.02 mm. All measurements were meticulously recorded for each individual specimen. These measurements encompassed the carapace length (CL), carapace width (CW), abdomen width (AW), abdomen length (AL), chelar propodus width (ChW), chelar propodus height (ChH), merus width (MEW), merus length (MEL), and dactyl length (DL). Each measurement (Figure 2) contributes to a comprehensive understanding of the crab’s physical characteristics and aids in elucidating various aspects of its ecology and biology.

2.5. Population Structure Measurement: Length/Weight−Weight Relationship

Carapace width frequency (CWF) data of the experimental specimens were grouped in 1 cm class intervals. In addition, the carapace width–body weight relationship was determined by LWRs following W = a × CWb, where W is the body weight (g) and CW represents the carapace width (cm) [21]. Further, LLRs, i.e., carapace width (CW) vs. carapace length (CL) was assessed with a linear regression analysis, as followed by Sabbir et al. [22].

2.6. Marketing Channel Studies

To assess the marketing status of V. litterata, a field-based market survey was conducted from March to April 2023 across six local markets where these crabs are available, within the two coastal districts, Khulna (n = 4) and Bagerhat (n = 2), Bangladesh. Data were collected through semi-structured interviews and direct observations from fishermen (n = 5 individual/sampling point, during crabs collection), vendors (n = 5 individual/market), and consumers (n = 5 individual/market) regarding the crab’s source, price trends, and seasonal availability. All data were recorded systematically for further analysis.

2.7. Statistics

All the statistical analyses were conducted using SPSS software (Version 28, SPSS Inc. IBM, New York, NY, USA). The Shapiro–Wilk test (n < 30) was employed to assess the normal distribution of the dataset. Sex ratio differences between males and females were assessed using the Chi-square (χ2) test. An analysis of covariance (ANCOVA) was performed on body measurements, with sex treated as the independent factor, to compare the relationships between morphological traits across sexes. Graphs were produced with MINITAB (Version 17.1.0) and Microsoft Excel 365 (Microsoft® Excel, Redmond, WA, USA).

3. Results

3.1. Sex Ratio, Gonad Maturation Status

A total of 75 individuals of V. litterata were recorded during the study period. Among them, 35 were identified as males and 40 as females, resulting in an overall male-to-female ratio of approximately 1:1.14. However, the observed sex ratio (35♂:40♀) does not significantly differ from the expected 1:1 ratio (Chi-square statistic, χ2 = 0.33, df = 1, p = 0.56). Thus, the observed sex ratio indicated that the female population was greater than the male population during the study period. Based on visual observation of ovary development, four distinct maturation stages were identified: immature ovary (Stage I), early maturing ovary (Stage II), late maturing ovary (Stage III), and fully mature ovary (Stage IV) (Figure 3).
The distribution of ovarian maturation stages among the female specimens showed that Stage IV (fully mature) ovaries were the most prevalent, accounting for 43% of individuals, followed by Stage III (late maturing) at 22%, Stage II (early maturing) at 20%, and Stage I (immature) at 15% (Figure 4). These results indicate a predominance of advanced gonadal development stages during the sampling period.

3.2. Morphometric Dynamics

Carapace Morphometry: Width Distribution and Length–Width Relationship

The major morphometric characteristics of V. litterata specimens collected from the Pasur River during the sampling period are presented in Table 1. There was no significant difference in body weight (BW) between sexes (ANCOVA, F = 2.8, p = 0.097), with males averaging 13.1 ± 4.3 g and females 12.66 ± 3.85 g. Similarly, no significant differences were observed in CW (F = 0.05, p = 0.82) and CL (F = 0.12, p = 0.73) between sexes, with CW averaging 31.2 ± 5.7 mm in males and 31.97 ± 5.80 mm in females, and CL averaging 29.3 ± 4.7 mm in males and 30.14 ± 4.91 mm in females. The CWFs of the experimental specimens showed that the size ranged from 19.1 to 44.2 mm CW. The minimum CW value was recorded from the male population, whereas CL ranged from 19.1 to 42.2 mm. The size-frequency distribution of carapace width (CWFs) differed between males and females. In females, the most abundant CWFs size classes were 28.99–29.99 mm and 33.99–34.99 mm, whereas in males the modal size class was 33.99–33.99 mm. Statistical comparison using a Kolmogorov–Smirnov test indicated no significant difference in the overall CWFs distribution between sexes (p > 0.05), suggesting overlapping size ranges, although males tended to have slightly larger maximum sizes. (Figure 4). Only abdominal width (AW, ANCOVA: F = 6.2, p = 0.015) and dactyl length (DL, ANCOVA: F = 12.5, p = 0.001) differed significantly between males and females, with females showing higher AW values (21.84 ± 3.85 mm) than males (13.1 ± 4.3 mm), while the DL value was significantly higher in males (11.0 ± 2.69 mm) than in females (8.94 ± 0.71 mm). All other morphometric parameters, including abdominal length (AL), chelar propodus width (ChW), chelar propodus height (ChH), merus width (MEW), and merus length (MEL), showed no significant difference (Table 1).
The present study found that a strong correlation was found between body weight (BW) and carapace width (CW) in both sexes (R2 = 0.947 and 0.941 in males and females, respectively). The estimated growth exponent (b) indicated negative allometric growth in both cases, with males showing a value of 2.17, while females had a higher value of 2.62, indicating relatively greater weight gain with increasing carapace width in females compared to males (Figure 5), with all length–width relationships showing strong correlations. The carapace width (CW) and carapace length (CL) of V. litterata exhibited a strong positive linear relationship in both sexes. Males showed a slightly higher slope (b = 3.0856) compared to females (b = 2.4584), indicating that males tend to increase in width at a slightly greater rate relative to length during growth. The coefficient of determination was high for both males (R2 = 0.9383) and females (R2 = 0.9367), reflecting strong correlations and consistent growth patterns across individuals.
The regression analyses of other morphometric relationships, including abdominal width (AbW), abdominal length (AbL), carapace length (ChL), carapace height (ChH), and total weight (TW), between male and female V. litterata revealed strong and significant correlations, with all models showing high coefficients of determination (R2), indicating consistent and predictable growth patterns (Supplementary Figure S1).

3.3. Marketing Channels of V. litterata

V. litterata is an estuarine crab species commonly inhabiting the fresh and brackish coastal rivers of Bangladesh, particularly within the Sundarbans mangrove ecosystem. While this species remains largely unknown across much of the country, it is locally harvested and consumed in several coastal districts, including Khulna, Bagerhat, Barguna, Satkhira, and Jessore. Currently, no formalized or structured commercial marketing channels exist for V. litterata; instead, the species is primarily collected as bycatch during other fishing activities. Fishermen typically gather these crabs directly from coastal rivers and sell them to local fish vendors, who then distribute them to village and town markets, where they are purchased by local consumers for household consumption. Historically, the market price for V. litterata was modest, ranging from 50 to 70 BDT (approximately <$1 USD); however, recent local market data from Khulna (April 2024) indicate that rising demand has driven prices upward to 150–200 BDT (approximately $1.5–2 USD). Although formal trade networks have not yet been established, these trends point to an emerging market potential for V. litterata within Bangladesh’s coastal fisheries sector.

4. Discussion

In this study, we are trying to describe the general morphological and reproductive parameters including sex ratio, ovarian development, and breeding season, of the ecologically endangered crab V. litterata, in order to know their stock and potential for commercial culture. In crustaceans, the sex ratio is a crucial biological parameter, which is important for understanding their population structure and reproductive biology. In the current study, the average sex ratio of Varuna litterata was 1:1.14, indicating a female-biased population during the study period, although the expected theoretical sex ratio of any crab species is 1:1 [1,22,23]. However, depending on the animal’s maturation stage, migratory behavior, seasons, and other environmental factors, the ratio may differ from 1:1 [6,14,23]. As observed previously, V. litterata exhibits seasonal migratory behavior, with upstream migration restricted to a specific period of the year that is strongly influenced by tidal fluctuations [12,14]. Consequently, the species is not continuously present in the study area, limiting the ability to assess seasonal or temporal variations in sex ratio and morphological traits. In this case, our study therefore reflects only the specific sampling window, and may differ from year-round trends reported in other studies. However, a similar sex ratio has been observed in the estuarine mud crab Scylla olivacea (1:1.01) in the north-eastern Sundarbans, Bangladesh [23], Scylla serrata (1:1.13) crabs from the in Coringa mangroves, Andhra Pradesh, India [24], and the portunidae crab Charybdis natator (1:1.10) from Nagapattinam, on the south east coast of the Bay of Bengal [25]. Shanmugam and Bensam [26] reported similar female dominance in sex in Scylla serrata from the adjacent tuticorin port, Tamil Nadu, from January to March, while Ram and Chandramohan [27] noted higher female catches for blood-spotted swimming crab (Portunus sanguinolentus) during March to May, in the Netravati estuary. This trend has also been documented in various estuarine and coastal regions by other researchers, including Srinivasagam [28] in the Killai backwaters, Srinivasagam [26] in Pulicat Lake, Lalitha Devi [29] in the Kakinada mangroves. These consistent patterns suggest that environmental and biological factors may favor a seasonal predominance of females in crab populations.
The morphometric analysis of V. litterata revealed notable sexual dimorphism across all measured parameters, with males and females exhibiting distinct size variations. Carapace width (CW), a key indicator of overall size, was significantly greater in females (31.97 ± 5.80 mm) compared to males (31.2 ± 5.7 mm), indicating that females tend to grow larger for reproductive adaptations such as egg carrying. However, body weight (BW) was higher in males (13.1 ± 4.3 g) than females (12.66 ± 3.85 g), which may relate to fast growth in males. The dominant carapace width class in both males and females centers around 33–34 mm, suggesting a relatively mature or abundant age group, while females exhibit a slightly wider distribution with more individuals at both lower and higher CW classes compared to males. In contrast, males showed greater values in cheliped height (ChH: 8.4 ± 0.6 mm) and length (ChL: 16.0 ± 2.2 mm), which may reflect a role in territorial defense or mating competition. Abdomen width (AW) and abdomen length (AL) were consistently larger in females (21.84 ± 3.85 mm and 23.33 ± 4.09 mm, respectively), likely supporting reproductive functions such as egg brooding. Measurements of mouthpart elements such as maxilliped endopod width (MEW) and length (MEL) also showed slight male dominance in size, though with smaller differences. Dactyl length (DL) was greater in males (11.0 ± 2.69 mm) compared to females (8.94 ± 0.71 mm), reinforcing the pattern of larger appendage dimensions in males, and our observation was highly supported with the biology of V. litterata from Cochin backwaters, Kerala, India [30], and in blue crab, Callinectes sapidus [31]. Overall, the combined data (n = 75) present intermediate values between sexes, reflecting the influence of both male and female morphologies in the population. This morphometric differentiation likely reflects ecological roles and reproductive strategies between sexes in V. litterata [32,33]. While our study did not directly observe behavior, we can assume that the larger abdominal width and dactyl length in females likely relates to reproductive roles, whereas males may exhibit morphologies linked to agonistic interactions. Although ontogenetic allometry and sampling gear selectivity could contribute, the consistent sexual dimorphism in these traits supports an ecological and reproductive explanation.
Growth patterns in aquatic organisms are generally categorized into isometric and allometric growth [33,34]. In isometric growth, the body proportions remain constant as the organism grows, with a b value of exactly 3.0 in the LWR equation (W = aL^b). This suggests that in the case of this allometric growth, the crab’s weight increases at a slower rate than its length: a pattern commonly observed in species that allocate more energy toward reproduction or mobility, rather than proportional somatic growth. In the present study, V. litterata exhibited negative allometric growth, as indicated by the overall b value for males around 3.0 and for females less than 3.00. Similar patterns of allometric growth have been reported in intertidal crabs such as Tubuca seismella and T. signata from the Ross River Estuary and Pallarenda Creek near Townsville, Queensland, Australia [35], as well as in several brachyuran crab species along the eastern Atlantic coast of the USA [36].
The length–weight relationships (LWRs) demonstrated a strong correlation, with all r2 ≥ 0.941, confirming the reliability of the data and consistency in growth patterns. Similarly, the length–length relationship (LLR) between carapace width (CW) and carapace length (CL) also showed a high degree of correlation (r2 ≥ 0.935), further supporting the precision of morphometric measurements. Our results revealed sex-based differences in standardized claw centroid size across all four studied species, indicating that the presence of sexual dimorphism in claw size among intertidal mangrove crabs is supported by the data published for mangrove crabs in Bangladesh and India [2,25]. In contrast, allometric growth occurs when body proportions change with size. If b < 3, it is negative allometric growth, indicating that the organism becomes relatively slimmer as it grows. If b > 3, it is positive allometric growth, suggesting the organism becomes bulkier with size; this knowledge is very necessary for the conservation status. The negative allometric growth in V. litterata likely results from ecological and biological factors such as habitat conditions, life stage, and energy allocation [6,22,23]. Although we did not directly measure environmental covariates such as salinity, temperature, or substrate, previous studies have shown that habitat conditions, food availability, and life stage can influence morphometric traits in Varuna litterata [32,33,37]. Therefore, the observed negative allometric growth likely reflects a combination of ecological and biological factors, including energy allocation and habitat variability. Future studies incorporating environmental measurements would help clarify these relationships. As a semi-terrestrial estuarine crab, it may favor carapace expansion for mobility or defense over weight gain. The weaker carapace size–mass relationship may reflect molting-related growth [33,34]. This strategy enhances survival and reproductive success in dynamic estuarine environments.
Crabs are essential components of mangrove-estuarine ecosystems, playing significant ecological roles in the maintenance, alteration, and regulation of these environments [2,6]. V. litterata, though not widely consumed, holds significant nutritional and economic potential. Traditionally, it has been eaten by some coastal communities in Bangladesh, parts of India (West Bengal), and the Philippines, but broader public awareness remains low [10]. However, in recent years, demand for this species has been gradually increasing in Bangladesh due to its remarkable nutritional profile [38]. According to Sinaga et al. [18], V. litterata contains 25.66% protein, 8.52% carbohydrates, 0.52% fat, 4.57% ash, and 60.72% water—making it a superior protein source compared to other brachyuran crabs like mud crabs (15–25% protein) and Portunus pelagicus (23.8 g/100 g protein), as reported by Paul et al. [2] and Shibana et al. [36]. Its high protein and low fat content make it ideal for healthy, protein-rich diets, while the moderate carbohydrate and mineral content enhance its value as a balanced seafood option [16,38]. V. litterata is more widely appreciated in countries like the Philippines and Thailand, with Thailand alone consuming around 18,000 tons annually—6000 tons of which are imported due to local production shortfalls [16,17,39].
Bangladesh, with its extensive estuarine and coastal ecosystems that naturally harbor V. litterata, is uniquely positioned to seize this demand gap as a strategic market opportunity. Bangladesh possesses vast coastal and estuarine ecosystems that naturally support V. litterata, a crab species with high nutritional value but limited consumer awareness [4,6,39]. Given Bangladesh’s existing aquaculture expertise, especially in mud crab farming, developing the commercial production of V. litterata could offer a new source of livelihood and income for coastal communities. With proper investment in breeding, sustainable harvesting practices, and capacity-building programs, this species could support both domestic nutrition and export potential. Promoting V. litterata as a nutritious, locally available seafood option can help improve food security, reduce dependency on imported animal proteins, and contribute to the blue economy through diversified aquaculture initiatives.

5. Conclusions

This study provides the first comprehensive account of the reproductive biology, morphometric characteristics, and market prospects of V. litterata in Bangladesh. The findings highlight a female-biased sex ratio and a predominance of mature ovarian stages during the peak breeding season (March–April), indicating active reproductive activity in the population. Morphometric analysis revealed distinct sexual dimorphism and consistent growth patterns, with carapace width emerging as a reliable predictor of both length and weight. The observed negative allometric growth suggests energy allocation toward reproductive and ecological functions, rather than proportional size. Despite its ecological presence and nutritional value, this crab remains antiquated in commercial markets, yet its rising demand, high protein content, and suitability for local aquaculture highlight its strong potential for commercial development. So, integrating V. litterata into Bangladesh’s coastal fisheries and aquaculture strategies could offer a sustainable avenue for enhancing food security, supporting rural livelihoods, and contributing to the development of the blue economy.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/hydrobiology4040027/s1. Supplementary Figure S1. Morphometric Relationships between male and female V. litterata Among Abdominal Width (AbW), Abdominal Length (AbL), Carapace Height (ChH), Carapace Length (ChL), and Total Weight (TW).

Author Contributions

Conceptualization, J.B.; methodology, J.B.; software, J.B., W.S. and P.P.; formal analysis, J.B., W.S. and P.P.; data curation, J.B.; writing—original draft preparation, J.B., P.P., K.S. and R.D.; writing—review and editing, J.B., W.S., K.S. and R.D.; visualization, J.B., W.S. and K.S.; All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The animal study protocol was approved in accordance with the guidelines and regulations of the Biosafety and Ethics Committee at Khulna University Research and Innovation center, Bangladesh (Approval code: KUAEC-FMRT/09/2023).

Informed Consent Statement

Not applicable.

Data Availability Statement

Data available on request.

Acknowledgments

Biosafety and Ethics Committee at Khulna University Research and Innovation Center.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Map showing the actual position of four sampling locations with the coordinate across the Pasur River, Bangladesh.
Figure 1. Map showing the actual position of four sampling locations with the coordinate across the Pasur River, Bangladesh.
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Figure 2. Major morphometrics measurements include carapace length (CL) and carapace width (CW) (A), abdomen width (AW) and abdomen length (AL) (C,D), chelar propodus width (ChW), chelar propodus height (ChH), merus width (MEW), merus length (MEL), and dactyl length (DL) (B).
Figure 2. Major morphometrics measurements include carapace length (CL) and carapace width (CW) (A), abdomen width (AW) and abdomen length (AL) (C,D), chelar propodus width (ChW), chelar propodus height (ChH), merus width (MEW), merus length (MEL), and dactyl length (DL) (B).
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Figure 3. Visual classification of ovary development stages in V. litterata collected from the Pasur River from March to April 2023, Khulna, Bangladesh. (A): Immature ovary (Stage I), (B): early maturing ovary (Stage II), (C): late maturing ovary (Stage III), and (D): fully mature ovary (Stage IV). Arrows indicate the ovaries at each respective stage. Scale bar: 200 µm (A–C), 100 µm (D).
Figure 3. Visual classification of ovary development stages in V. litterata collected from the Pasur River from March to April 2023, Khulna, Bangladesh. (A): Immature ovary (Stage I), (B): early maturing ovary (Stage II), (C): late maturing ovary (Stage III), and (D): fully mature ovary (Stage IV). Arrows indicate the ovaries at each respective stage. Scale bar: 200 µm (A–C), 100 µm (D).
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Figure 4. Frequency distributions of male, female, and combined individuals of V. litterata, collected from the Pasur River. Blue bar: male, pink: female, and gray: combined male and female crabs carapace width.
Figure 4. Frequency distributions of male, female, and combined individuals of V. litterata, collected from the Pasur River. Blue bar: male, pink: female, and gray: combined male and female crabs carapace width.
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Figure 5. Relationships between body weight and carapace width (BW-CW) and carapace width and carapace length (CW-CL) in male and female V. litterata, collected from the Pasur River, adjacent to the Sundarbans mangrove forest, Bangladesh.
Figure 5. Relationships between body weight and carapace width (BW-CW) and carapace width and carapace length (CW-CL) in male and female V. litterata, collected from the Pasur River, adjacent to the Sundarbans mangrove forest, Bangladesh.
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Table 1. Major morphometric measurements (Mean ± SD) of V. litterata crabs collected from the Pasur River. CL = carapace length, CW = carapace width, AW = abdomen width, AL = abdomen length, ChW = chelar propodus width, ChH = chelar propodus height, MEW = merus width, MEL = merus length, and DL = dactyl length. Different letters indicate significant differences between male and female groups (ANCOVA, p < 0.05).
Table 1. Major morphometric measurements (Mean ± SD) of V. litterata crabs collected from the Pasur River. CL = carapace length, CW = carapace width, AW = abdomen width, AL = abdomen length, ChW = chelar propodus width, ChH = chelar propodus height, MEW = merus width, MEL = merus length, and DL = dactyl length. Different letters indicate significant differences between male and female groups (ANCOVA, p < 0.05).
Morphometric FeatureMale, n = 35Female, n = 40Combined, n = 75
Mean ± SDMaxMinMean ± SDMaxMinMean ± SDMaxMin
CW (mm)31.2 ± 5.744.219.131.97 ± 5.8042.221.321.92 ± 4.7731.8511.7
CL (mm)29.3 ± 4.739.220.430.14 ± 4.9139.520.630.65 ± 5.2640.720.85
BW (g)13.1 ± 4.323.23.912.66 ± 3.8519.54.321.63 ± 4.6131.3512.25
AW (mm)13.1 ± 4.3 a21.14.821.84 ± 3.85 b29.113.617.46 ± 4.06 c25.19.2
AL (mm)21.2 ± 4.429.713.723.33 ± 4.0929.815.222.27 ± 4.2229.7514.45
ChL (mm)16.0 ± 2.223.31215.09 ± 2.1722.411.115.54 ± 2.1822.8511.55
ChH (mm)8.4 ± 0.69.57.47.11 ± 0.588.26.17.74 ± 0.588.856.75
MEW (mm)6.6 ± 1.408.43.85.61 ± 0.847.44.36.09 ± 1.127.94.05
MEL (mm)11.4 ± 2.6816.47.610.53 ± 1.2912.88.510.98 ± 1.9814.68.05
DL (mm)11.0 ± 2.69 a16.57.58.94 ± 0.71 b10.37.89.96 ± 1.70 b13.47.65
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MDPI and ACS Style

Bir, J.; Paul, P.; Sabbir, W.; Sumon, K.; Das, R. Morphological and Meristic Feature Studies and Marketing Status of Peregrine Crab Varuna litterata from a Coastal Estuary in Sundarbans Mangrove Forest, Bangladesh. Hydrobiology 2025, 4, 27. https://doi.org/10.3390/hydrobiology4040027

AMA Style

Bir J, Paul P, Sabbir W, Sumon K, Das R. Morphological and Meristic Feature Studies and Marketing Status of Peregrine Crab Varuna litterata from a Coastal Estuary in Sundarbans Mangrove Forest, Bangladesh. Hydrobiology. 2025; 4(4):27. https://doi.org/10.3390/hydrobiology4040027

Chicago/Turabian Style

Bir, Joyanta, Prianka Paul, Wasim Sabbir, Khirujjaman Sumon, and Rimu Das. 2025. "Morphological and Meristic Feature Studies and Marketing Status of Peregrine Crab Varuna litterata from a Coastal Estuary in Sundarbans Mangrove Forest, Bangladesh" Hydrobiology 4, no. 4: 27. https://doi.org/10.3390/hydrobiology4040027

APA Style

Bir, J., Paul, P., Sabbir, W., Sumon, K., & Das, R. (2025). Morphological and Meristic Feature Studies and Marketing Status of Peregrine Crab Varuna litterata from a Coastal Estuary in Sundarbans Mangrove Forest, Bangladesh. Hydrobiology, 4(4), 27. https://doi.org/10.3390/hydrobiology4040027

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