Limnology and Freshwater Biology

A decade of Philippine freshwater goby research (2010–2022): a systematic review and meta‑analysis of ichthyofaunal surveys

Baron C.T., Garces J.J.C. — Thu, 18 Jun 2026 00:00:00 +0800

Freshwater goby (Family Gobiidae) is one of the diverse and widespread fish species in rivers and lakes, with economic values ranging from ornamental and subsistence provisions. Several ichthyofaunal surveys have been conducted in the Philippines; however, no systematic review and meta-analysis was performed to analyze freshwater goby species richness over fish species richness. Following the PRISMA Protocol, twenty–three (23) studies were assessed and statistically analyzed using JASP Version 0.18.3. Each paper was reviewed to identify study sites, goby genera, diversity indices (Shannon, Pielou’s evenness, and Simpson), and physicochemical parameters, with correlations analyzed across fish species, goby species richness, and diversity indices. Results revealed that most freshwater goby studies take place in Luzon, and the genus Glossogobius is the prevalent goby species at most study sites. The diversity index for introduced fish species ranged from low to medium, as indicated by the enriched biodiversity index score from Guerrero (2014). In terms of physicochemical parameters, all values generally met the standards set by DAO 2016-08. However, the forest plot revealed that the effect size was entirely on the positive side of zero, with a combined effect size of 0.46, suggesting a moderate impact. The funnel plot indicated an asymmetrical pattern among studies, suggesting potential publication bias. Analysis suggests that goby diversity in the Philippines is high in terms of species richness, with a moderate effect size when compared to overall fish species richness based on the collated studies. Taking into account the high publication bias observed, we recommend including more studies from Southeast Asian countries. Researchers are encouraged to prioritize biodiversity studies in the Visayas and Mindanao regions to mitigate study bias. A comparative analysis of native and introduced fish species richness would also be beneficial in determining their potential impact on the overall effect size of species richness.

Assessment of water quality and zooplankton community structure in the Gambhiri River (Chittorgarh, Rajasthan, India)

Kumar S., Veerwal B., Garwa H. — Thu, 18 Jun 2026 00:00:00 +0800

This study examines water quality parameters and zooplankton community structure in the Gambhiri River, Chittorgarh district of Rajasthan, India, to assess the ecological health and trophic state of this vital freshwater ecosystem. Seasonal sampling was conducted from January to December 2023 at six sampling sites to observe spatial and temporal variations in physicochemical parameters and zooplankton communities. Key water quality parameters, including water temperature, pH, total dissolved solids, turbidity, electrical conductivity, total hardness, chloride, alkalinity, dissolved oxygen, and biological oxygen demand, were measured using standard analytical techniques. Zooplankton samples were collected with a plankton net, preserved, and identified to the lowest possible taxonomic level, following standard keys. In the study period, 65 species of zooplankton were analyzed, of which 26 species of Rotifera, 25 species of Cladocera, 8 species of Copepoda, and 6 species of Ostracoda were recorded. Cladocera appeared as the dominant group of zooplankton with a higher density (38.67%), followed by Rotifera (35.72%), Copepoda (18.57%), and Ostracoda (7.03%). The season-wise zooplankton analysis revealed that Cladocera and Rotifera were the dominant groups across all seasons, while Copepoda and Ostracoda contributed comparatively less to the total density. Cladocera showed higher density than Rotifera during summer and post-monsoon seasons, whereas during monsoon and winter, Rotifera slightly dominated over Cladocera. Copepoda consistently remained the third dominant group in all seasons, while Ostracoda recorded the lowest density throughout the study period. The study highlights the importance of zooplankton as sensitive bioindicators for evaluating the health of freshwater ecosystems and recommends routine monitoring and pollution control measures to preserve the ecological integrity of this crucial water resource in Rajasthan’s semi-arid region.

Functional digestive morphology and feeding intensity of the halfbeak Zenarchopterus clarus (Hemiramphidae) in a tropical estuarine habitats, southern Vietnam

Nguyen V.Q., Tran A.N., Tran H.N.G., Nguyen T.Q., Nguyen H.T.K., Dinh Q.M. — Thu, 18 Jun 2026 00:00:00 +0800

This study examines the functional digestive morphology and feeding intensity of the halfbeak Zenarchopterus clarus (Hemiramphidae) in a tropical estuarine habitats of southern Vietnam. A total of 892 specimens were collected monthly from August 2024 to July 2025 at two estuarine sites. The species exhibited a superior mouth with an elongated lower jaw, dense conical dentition, well-developed pharyngeal tooth plates, and numerous gill rakers. The digestive tract consisted of a muscular esophagus and a short intestine, lacking a clearly differentiated stomach, indicating rapid processing of soft prey. Feeding intensity was evaluated using the gut-somatic index (GI) and analyzed with generalized linear mixed models. The model indicated significant variation in GI (p < 0.001). The GI differed significantly between sexes and sampling locations, with higher values in females and at Dam Doi. Although the season had no significant main effect, a significant sex × season interaction indicated contrasting seasonal feeding patterns between males and females. Morphological traits and GI collectively suggest that Z. clarus is adapted for surface-oriented feeding on small, mobile prey in dynamic estuarine environments. However, the feeding strategy was inferred from morphological traits and GI, as diet composition was not directly examined. These findings provide baseline insights into the digestive morphology and feeding ecology of an estuarine hemiramphid fish.

Problems of biological invasions in the fish fauna of southern Vietnam: the example of the Dong Nai River basin

Thu, 18 Jun 2026 00:00:00 +0800

Biological invasions of fish are among the key drivers of transformation in freshwater ecosystems, particularly in regions with intensive aquaculture development and high anthropogenic pressure. The aim of this study was to assess the extent of introduction and degree of naturalization of non-native fish species in the Dong Nai River basin (southern Vietnam), as well as to identify patterns of their spatial distribution and main pathways of introduction. Ichthyological sampling was conducted in April–May 2025 at 56 stations in the upper and middle reaches of the Dong Nai River, including the Da Nhim and Da Dang rivers, their tributaries, and lentic water bodies in Dong Nai and Lam Dong provinces. A total of 17 non-native fish species were recorded across 13 of the 17 surveyed areas. The highest diversity of introduced species was observed in large water bodies subjected to significant anthropogenic impact, particularly in Tri An Lake (11 species), as well as in the middle reaches of the Da Nhim River and the Dai Ninh Reservoir (6 species each). In contrast, the number of non-native species was considerably lower in highland areas of the Central Highlands (1–3 species), while no alien species were recorded in water bodies within Cat Tien National Park. Most species exhibited low to moderate occurrence frequency; however, two species—guppy (Poecilia reticulata Peters, 1859) and Nile tilapia (Oreochromis niloticus (Linnaeus, 1758))—showed very high prevalence. The results indicate a substantial scale of biological invasions in the Dong Nai River basin. Aquaculture and the aquarium trade are identified as the primary sources of non-native fish introductions, while their spatial distribution is strongly associated with the level of anthropogenic impact and the type of water body.

Paleohydrology of the Manych Strait in the Khvalynian basin of the Caspian Sea during the Late Pleistocene

Lavrentyev N.V. — Thu, 18 Jun 2026 00:00:00 +0800

The paper discusses controversial issues of the paleohydrology of the Manych Strait—a key element in the water exchange system between the Khvalynian basin of the Caspian Sea and the Neoeuxinian basin of the Black Sea during the Late Pleistocene. Special attention is paid to two parameters: the maximum level of the Khvalynian transgression and the height of the spillway threshold through the Manych depression. Geological-geomorphological analysis, digital terrain modelling, and hydraulic modelling in the HEC-RAS system allowed reconstructing scenarios of Caspian water discharge through the Manych valley. The modelling results indicate that the most probable maximum level of the Caspian Sea during the Early Khvalynian transgression was approximately 40 m a.s.l. with a spillway threshold at 31 m a.s.l. Hypothetical limits of the discharge capacity of the Manych Strait channel of the Khvalynian Caspian basin were also calculated. The results can be used in further research.