The aquatic gastropods of Malaysian Borneo have long existed in a scientific blind spot. While recent studies have highlighted trends in molluscan research, particularly among edible mollusks, significant knowledge gaps remain regarding freshwater gastropods in lotic and inland environments. Research has primarily focused on coastal wetlands, intertidal zones, and economically important mollusk species (Hamli and Al-Asif, 2021; Idris et al., 2017, 2022). Systematic reviews indicate that mollusks dominate aquatic invertebrate research in East Malaysia, with freshwater gastropods often receiving minimal attention. This has resulted in a fragmented understanding of the true diversity, distribution, and ecological roles of gastropods in freshwater systems (Al-Asif et al., 2022). While intertidal gastropod communities in Bintulu and coastal wetlands have been explored to some extent, research into inland lotic environments, such as streams in Betong, Sarawak, remains limited and sporadic (Hamli et al., 2024; Bidat et al., 2023). The study on freshwater gastropod diversity in the selected lotic environment in Betong represents one of the few efforts to investigate inland diversity. However, these findings have not yet been synthesized into a larger ecological framework for the state.

Freshwater gastropods, primarily from the Prosobranchia and Pulmonata groups, inhabit nearly all freshwater ecosystems except Antarctica, including rivers, marshes, ponds, and springs (Strong et al., 2008). They exhibit a wide range of morphological adaptations, such as spiral, conical, and planispiral shells, with varying shell thickness and operculum presence (Johnson et al., 2019). Morphological traits like shell shape, ornamentation, and operculum type are important in systematics and may also reflect adaptations to habitat characteristics (Dowle et al., 2015). These gastropods primarily feed on periphyton, algae, detritus, and biofilms, acting as either epifaunal or arboreal organisms depending on the habitat (Safitri et al., 2025). Their community structure and abundance are influenced by a combination of abiotic factors, such as temperature, dissolved oxygen, and calcium levels, as well as biotic factors, including predation, competition, and vegetation (Carobene et al., 2023).

Previous studies of freshwater gastropods in the Bintulu Division have identified it as a region with high freshwater gastropod diversity, documenting at least 13 edible species, more than in other areas (Hamli et al., 2013, 2019). However, compared to surveys in the Tonle Sap basin, which report approximately 16 freshwater gastropod species per site (Ng et al., 2020), the numbers in Sarawak remain relatively low. This discrepancy raises questions about sampling effort, habitat coverage, and taxonomic resolution. It suggests that further comprehensive surveys and refined identification methods are needed to better understand the true diversity and population structure of freshwater gastropods in the region.

Despite their ecological and socio-economic importance, freshwater gastropods in Sarawak remain understudied. The lack of comprehensive data on their diversity and distribution, coupled with declining traditional knowledge, poses challenges for conservation and sustainable use. Therefore, scientific documentation of gastropod species in natural habitats is urgently needed. The present study aims to document species occurrence and distribution patterns of freshwater gastropods in selected areas of Malaysian Borneo.

2. Materials and Methods

2.1 Ethical approval

No ethical approval was required to conduct the study.

2.2 Study area and duration

This study was conducted in freshwater environments at two locations in Sarawak, Malaysia such as Bintulu and Sungai Tuah in Kanowit, Sarawak, Malaysia. The research took place from April 2022 to January 2023, with the distance between the two locations being approximately 196 km (Figure 1). Three sampling stations were selected across the study sites: station 1 (3°12'41.3"N 113°05'34.5"E) in Kanowit, station 2 (3°12'22.73"N 113°5'3.40"E), and station 3 (3°12'29.18"N 113°4'30.50"E) in Bintulu.

2.3 Sampling technique

At each sampling site, triplicate samples were collected from all stations. Specimens were counted and randomly selected from each sampling point, then placed into labeled zip-lock bags for further processing. All collected specimens were preserved in 10% formalin and transported to the laboratory for identification.

2.4 Species identification

In the laboratory, specimens were photographed with a digital camera to capture the shell morphological characteristics essential for identification. Taxonomic identification was conducted using the morphological keys and descriptions provided by Bidat et al. (2023) and Köhler et al. (2004).

2.5 IPRS pond preparation and management

Gastropod assemblages were analyzed based on the total number of individuals recorded for each species at both locations. Abundance data were compiled into tables and figures to illustrate species composition and variations in population size across the sites. Distribution was assessed by documenting the presence or absence of each species at the three locations, enabling a comparison of shared and site-specific taxa. The analyses were descriptive, focusing on patterns of abundance and distribution without the use of inferential statistics. All data were analyzed using Microsoft Excel (Microsoft 360).

3. Results

3.1 Morphology description

During the study, a total of seven freshwater gastropod species were recorded, representing three families: Pachychilidae (Melanoides tuberculata,Sulcospira pageli, S. schmidti, S. testudinaria, Brotia costula), Nassariidae (Clea nigricans), and Paludomidae. (Figure 2).

A. Pachychilidae

Sulcospira Pageli (Thiele, 1908)

The shell is solid and measures between huge and extra-large (39–40 mm), with a dark brown to black coloration. It features an elongate, conic, and turreted shape. Due to apex erosion, only 7–9 flattened whorls are present. The sculpture includes a few faint spirals: three near the suture and two at the base of the body whorls. The aperture is oval with a straight outer lip.

Sulcospira schmidti (E. von Martens, 1908)

The shell is a dark black color and exhibits globular, conical, turreted, and elongated shapes. It has either a rounded or pointed basal lip and features spiral striae on the final body whorls. Although there is no axial sculpture, a spiral sculpture is present, and the operculum is oval.

Figure 2. A: Sulcospira Pageli (Thiele, 1908), B: Brotia costula (Rafinesque, 1833), C: Sulcospira schmidti (E. von Martens, 1908), D: Melanoides tuberculata (O. F. Müller, 1774), E: Sulcospira testudinaria (von dem Busch, 1842), F: Paludomus everetti E. A. Smith, 1894 G: Clea nigricans A. Adams, 1855.

Sulcospira testudinaria (von dem Busch, 1842)

This is a short, black conical shell that features 4 to 6 whorls and a smooth, inflated protoconch. The shell has spiral lirae but no axial lines. Its aperture is oval and somewhat extended at the base, and the shell's width is particularly notable compared to other species in the same genus.

Brotia costula (Rafinesque, 1833)

This shell is thick, conical, and dark brown, with a rounded periphery. Its solid structure features a pyramidal, turreted spire that is often eroded, consisting of 6 to 11 whorls that range in color from light to olive brown. The shell's surface is sculpted with axial ribs, nodules, and basal spiral ridges. The body whorls are quite large, and the aperture is oval—rounded at the bottom and pointed at the top.

Melanoides tuberculata (O. F. Müller, 1774),

This shell is medium-sized, brown, and occasionally marbled, featuring an elongate, slender, turreted shape. It typically has seven whorls, a result of a slightly eroded tip. The suture is shallow, the whorls are flattened, and there is no distinct sub-sutural depression. The aperture is small and ovate, slightly angled below, with a well-rounded, sharp outer lip and an inconspicuous inner lip.

B. Paludomidae

Paludomus everetti E. A. Smith, 1894

This is a small, solid shell with 3 to 4 whorls. It ranges in color from ochre to dark brown and has a globose body, an angular body whorl, and an imprinted suture. The shell displays longitudinal striations. The operculum is corneous, featuring a polished and somewhat concave exterior surface.

C. Nassariidae

Clea nigricans A. Adams, 1855

The shell is moderate in size, elongated, and dark brown. It has a smooth appearance and features about four inflated whorls. The outer lip is smooth and slightly sinuous.

3.2 Abundance and distribution

The family Pachychilidae was the most diverse and abundant, comprising five species with a total of 82 individuals: Melanoides tuberculata (17 individuals), Sulcospira pageli (18), S. schmidti (21), B. costula (14), and S. testudinaria (12). The Nassariidae family was represented solely by Clea nigricans, which had 14 individuals recorded. The Paludomidae family contained a single species, Paludomus everetti, with 24 individuals, representing the highest abundance among all recorded species (Figure 3).

The most widely distributed species were M. tuberculata, S. pageli, S. schmidti, and B. costula (Table 1). However, only B. costula was recorded at both study locations, Bintulu and Kanowit, while the remaining species were present at only one location each.

4. Discussion

4.1 Abundance patterns

The present study found that the family Pachychilidae dominated both in species richness and abundance, indicating its significant ecological presence in the freshwater systems of Malaysian Borneo. Pachychilids are widely distributed freshwater gastropods in tropical regions of Southeast Asia and exhibit diverse reproductive strategies, including viviparity, which contribute to their ecological success (Köhler et al., 2004). Their adaptability to freshwater habitats may explain their dominance in both diversity and numbers across the study sites.

4.2 Species specific habitat preferences

B. costula was the only species recorded at both Bintulu and Kanowit, suggesting greater ecological plasticity or broader habitat tolerance. Members of the genus Brotia are known to inhabit fast-flowing, well-oxygenated river systems and are viviparous, traits that enhance resilience across varying lotic environments (Köhler et al., 2012). In contrast, other Pachychilidae species (M. tuberculata, S. pageli, S. schmidti, S. testudinaria) were found at only one location, indicating more restricted habitat preferences or sensitivity to local environmental variables (Bae and Park, 2020; Köhler et al., 2004). A study from Betong (Sarawak) reported a high abundance of S. pageli, along with B. costula and Clea nigricans, in streams and riverbanks with fast flows, suggesting these species favor such microhabitats (Bidat et al., 2023). This aligns with current findings, where these taxa, particularly B. costula, demonstrated broader distribution across study locations.

4.3 Ecological implications and future directions

The dominance of Pachychilidae in this study likely reflects their adaptability in reproduction, particularly through viviparity, the production of large egg capsules, and tolerance of variable freshwater conditions—traits that demonstrate resilience and provide a colonization advantage (Köhler et al., 2004). The presence of B. costula at both study sites suggests it may serve as a useful indicator species for well-oxygenated, flowing freshwater systems, while the other species recorded could indicate more localized ecological conditions. To further elucidate species-specific patterns, future studies should incorporate assessments of abiotic factors such as water flow, substrate type, dissolved oxygen levels, and habitat structure, along with community metrics like the Shannon–Weiner diversity and evenness indices.

5. Conclusions

This study documented seven freshwater gastropod species across three families—Pachychilidae, Nassariidae, and Paludomidae—at two locations in Malaysian Borneo. The family Pachychilidae was the most diverse and abundant, with B. costula being the only species recorded at both sites, indicating its broader ecological tolerance compared to other species. The limited occurrence of other species reveals specific habitat preferences, water quality requirements, and restricted dispersal abilities associated with the viviparous reproductive mode characteristic of Pachychilidae. These findings underscore the influence of biological traits and environmental conditions on freshwater gastropod distribution in Borneo. Future studies that integrate assessments of abiotic factors and diversity indices will further elucidate the ecological factors influencing gastropod assemblages in tropical freshwater ecosystems.

Acknowledgements

The author would like to thank the deanery and staff from the Department of Animal Science and Fishery, Universiti Putra Malaysia Sarawak, for the technical and logistic support and laboratory facilities provided.

Data availability statement

All data are presented inside the manuscript.

Informed consent statement

Not applicable.

Conflict of interest

The authors declare no conflict of interest.

Author contributions

Sonia Samban Betty: conceptualization, research, formal analysis, original draft writing, review, and editing; Nelina Edmond: formal analysis, writing, editing, and reviewing; Amy Halimah Rajaee: writing, editing, and reviewing; Johan Ismail: conceptualization, supervising, writing, editing, and reviewing; Hadi Hamli: supervising, conceptualization, review, and editing. All authors critically reviewed the manuscript and agreed to submit final version of the article.