Taxonomic work on the land snail genus Sarika Godwin-Austen, 1907 in Cambodia is scarce. A total of three species were recognized from Cambodia prior to this study. However, their taxonomic descriptions were based mainly on shell morphology, with limited genital data. To address this knowledge gap, we opportunistically surveyed for land snails in Cambodia. Our inventory yielded four species of Sarika – one recognized species, Sarika bocourti (Morelet, 1875), from Battambang Province and three new species, Sarika khmeriana Pholyotha & Panha sp. nov., Sarika lactoconcha Pholyotha & Panha sp. nov. and Sarika nana Pholyotha & Panha sp. nov. from Kampot and Takeo Provinces in southern Cambodia. Our discovery involves the first species of Sarika to be described from Cambodia in more than a century highlights the extent to which the diversity of Cambodian land snails remains to be discovered. The status of two species, Sarika benoiti (Crosse & Fischer, 1863) and Sarika resplendens (Philippi, 1846), is at present ambiguous because no material identifiable as these species was found in recent extensive surveys. Although S. bocourti was recently collected from Cambodia, its taxonomic position remained unclear due to a lack of living specimens. Detailed descriptions and illustrations of living animals, shell morphology and reproductive anatomy are provided, and a map showing their distributions is given.

Migratory fishes of the Mekong Basin are facing challenges from human-induced stressors. Quantifying the patterns of fish’s early life stages provides important information on spawning seasons, spawning and nursery habitats, reproductive strategies, migration and dispersal patterns, and stock status. However, the ecology of the Mekong larval fishes, including patterns and drivers of larval fish dispersal, is not well understood. Here, we investigate the temporal variability of drifting larval and juvenile fish assemblages in the Cambodian Mekong River and identify their environmental drivers using long-term (10 year) daily fish larval/juvenile data collections. We found that, in the Mekong main channel, the larval and juvenile assemblages were dominated by longitudinal migrants from the families Cyprinidae and Pangasiidae. Peak abundance and richness were found to occur in July and August, respectively. We detected a significant decline in larval and juvenile abundance and richness over the study period. Cross-wavelet analysis revealed that water levels always lead larval abundance, but lag richness. In addition, cross-correlation analysis observed that peak abundance and richness occurred eight weeks and one week, respectively, before the peak water level. We also discovered that species abundance and richness had a strongly positive relationship with maximum water levels. Variation in fish larval and juvenile abundance and richness was also related to total phosphorus, nitrate, alkalinity, and conductivity. Maximum water levels and the key water quality parameters (e.g., phosphorus, nitrate, alkalinity, and conductivity) significantly influence larval and juvenile fish abundance and richness patterns. Therefore, safeguarding natural seasonal flows, especially maximum flows associated with the peak flood pulse, as well as maintaining good water quality, are key to the reproductive success of many migratory fishes and effective dispersal of offspring to the lower floodplain for nursing, rearing, and growth. Clean and unregulated rivers support productive and diverse fisheries.

The Tonle Sap Lake in Cambodia supports several species of threatened megafish and contains one of the largest networks of freshwater fish reserves in the world. Despite these traits, this system remains understudied in terms of its utility for endangered fish conservation and restoration. This study was the first of a series of planned fish releases designed to test the effectiveness of conservation supplementation programs in the Tonle Sap Lake. In March 2022 (during the dry season), 1582 captive-reared fishes, including 1538 striped catfish Pangasianodon hypopthalmus, 42 giant barb Catlocarpio siamensis, and two Mekong giant catfish Pangasianodon gigas, were tagged and released into a 986-hectare fish reserve to assess post-release dispersal and survival. Brightly colored external tags with unique identification numbers were used to facilitate tag returns. A high-profile release event was held to raise awareness about the activity, bringing attention to the importance of fish reserves and endangered species conservation, and disseminating information about the research and tag return and reward program. This, in concert with other efforts, served to be an important education and outreach tool and increased tag return rates. We found that mortality from fishing was rapid and very high. Nineteen percent of released fishes were recaptured in the first 2 days after the fish release, and 46% were recaptured by day 83 after the release, indicating intense fishing pressure on the Tonle Sap Lake fisheries. Eighty percent of recaptured fishes were caught in stationary gill nets, most within 10 km of the release site. Fishing mortality rates were independent of fish size or source (pond-reared or cage-reared). Environmental DNA (eDNA) was found to be capable of detecting each of these species’ presence in the water at the release site and could prove to be a useful tool for endangered species monitoring and restoration. Future research should explore alternative release timing, release location, and other methods of increasing post-release survival. Ultimately, underlying sources of mortality, especially fishing, will need to be addressed for conservation supplementation programs to succeed in the Tonle Sap Lake. Conservation supplementation should not be viewed as a substitute for more fundamental conservation measures, such as maintenance of environmental flows, preservation of ecological connectivity, and science-based fisheries management.

Striped catfish Pangasianodon hypopthalmus (Sauvage, 1878) is a flagship catfish species of the Mekong River region, a commercially valuable food fish that is important in freshwater fisheries, and a popular aquaculture species in many Asian countries. The species was assessed as “Endangered” by the International Union for Conservation of Nature (IUCN) due to range contraction and declining abundance, though the status of the species’ wild population in Cambodia, a critical habitat for the species, is not well understood. Here, we assess the population status of the striped catfish in Cambodia using multiple sources, including time-series catch data and length frequency distribution data from a commercial fishery (stationary trawl bagnet or dai) operated in the Tonle Sap River from 1998/99 to 2017/18 and larval drift data monitored in the Mekong River in Phnom Penh from 2004 to 2018. We found that there was a significant decline (R² = 0.54, p = 0.0002) in the catch (metric tonnes) of the striped catfish from the commercial dai fishery over the last two decades. Similarly, length-based indicator analysis indicates that striped catfish mean length and abundance have both declined over the study period, raising concerns about the sustainability of river catfish fisheries. Moreover, long-term larval drift monitoring in Mekong River shows that there was a marginally significant decline in the quantity of striped catfish larvae/juvenile drifting downstream to the lower floodplain over the last decade. Changes in flood index (extent and duration of flood) in the Tonle Sap floodplain affected by the Mekong’s flow are likely key factors driving the decline of the wild populations of the striped catfish. Both larval fish abundance and floodplain fish harvests have a significant positive relationship with Mekong flow and flood extent. Indiscriminate fishing exacerbates pressures on striped catfish stocks. Therefore, actions such as maintaining natural seasonal flows (flood timing, extent, and duration) to the Tonle Sap floodplain and protecting migratory fish stocks from overharvest and habitat fragmentation are essential to the persistence of stocks of striped catfish and other large-bodied migratory fishes that utilize both the Cambodian Mekong and Tonle Sap floodplains.

A new species of the wholly freshwater hymenosomatid crab genus Limnopilos Chuang & Ng, 1991, is described from Tonle Sap River in the lower Mekong drainage, Cambodia. This is the fourth species known, and the second one from Indochina. The type species, of Limnopilos, L. naiyanetri Chuang & Ng, 1991, was from the Chao Phraya drainage to the west in central Thailand. The new species is characterized by the presence of a rostrum, relatively shorter ambulatory legs and a different structure of the male first gonopod. Limnopilos sumatranus Naruse & Ng, 2007, is also recorded from southern Peninsular Malaysia for the first time.