Heok Hui Tan

• PhD (NUS)
• Museum Collections, Curator of Ichthyology at National University of Singapore

This study describes Pterocryptis vorax , a new species of silurid catfish from the upper reaches of the Temburong River drainage in Brunei Darussalam, northern Borneo. Pterocryptis vorax is distinguished from congeners in having a unique combination of the following characters: rictal lobe ending at vertical posterior to posterior orbital margin,...

Freshwater ecosystems are highly biodiverse¹ and important for livelihoods and economic development², but are under substantial stress³. To date, comprehensive global assessments of extinction risk have not included any speciose groups primarily living in freshwaters. Consequently, data from predominantly terrestrial tetrapods4,5 are used to guide...

A comparison of the recent description of Chelonodontops bengalensis Habib, Neogi, Og, Lee & Kim 2018 with that of Tetrodon patoca Hamilton 1822 reveals that the former is a junior synonym of the latter. Chelonodon patoca appears to be restricted in its distribution to coastal brackish waters at the mouth of the Ganges/Brahmaputra/Meghna system in...

Pseudomystus tuberosus, a new species of bagrid catfish from the Kahayan River drainage in south central Borneo, is described in this study. It can be distinguished from all congeners in having a strongly humped dorsal profile (vs. dorsal profile weakly humped or without hump), as well as its head and flanks covered with rounded tubercles (vs. smoo...

Logged and disturbed forests are often viewed as degraded and depauperate environments compared with primary forest. However, they are dynamic ecosystems¹ that provide refugia for large amounts of biodiversity2,3, so we cannot afford to underestimate their conservation value⁴. Here we present empirically defined thresholds for categorizing the cons...

There is an urgent need for reliable data on the impacts of deforestation on tropical biodiversity. The city-state of Singapore has one of the most detailed biodiversity records in the tropics, dating back to the turn of the 19th century. In 1819, Singapore was almost entirely covered in primary forest, but this has since been largely cleared. We c...

We report the discovery of several specimens of the genus Encheloclarias Herre & Myers, 1937, in Singapore, from Nee Soon Swamp Forest in the Central Catchment Nature Reserve. Morphological comparisons with type specimens of various Encheloclarias species revealed the Singapore specimens belong to Encheloclarias kelioides Ng & Lim, 1993. This disco...

Uropterygius cyamommatus, new species, is described based on nine specimens from limestone anchialine caves in Christmas Island and Panglao Island. This species is a small-sized, elongated moray eel belonging to the uniform brown-coloured species group of the genus. It differs from all congeners of Uropterygius in having very small eyes (3.0-4.6% o...

The rare clariid catfish genus Encheloclarias is recorded for the first time from the peat swamp habitat in Brunei Darussalam, representing its northernmost record on the island of Borneo. Upon detailed examination, the Brunei species is keyed out to E. baculum. Using fresh material from Brunei and Sarawak (Malaysia, Borneo), the taxonomic status o...

Non-native fishes are widespread in Hong Kong and many are likely to be established. Extensive field surveys, literature reviews, and citizen science data were used to determine the diversity, geographic distribution, potential introduction sources, and known impacts of non-native freshwater fishes in Hong Kong. In total, 95 species, including five...

Food webs summarise trophic interactions of the biotic components within an ecosystem, which can influence nutrient dynamics and energy flows, ultimately affecting ecosystem functions and services. Food webs represent the hypothesised trophic links between predators and prey and can be presented as empirical food webs, in which the relative strengt...

The African sharptooth catfish, Clarias gariepinus , is a globally invasive species with known severe impacts, including native species declines through ecological (e.g., competition, predation) and genetic interactions (e.g., hybridisation, introgression). The species was introduced to the Malay Peninsula in the late 1980s, and has since become wi...

Two new species of blackwater catfishes are described from Pulau Natuna Besar of the Natuna Archipelago, Indonesia. Silurichthys insulanus (Siluridae), new species, differs from all congeners in having a combination of characters: eye diameter 8% HL; pectoral-fin length 16.0% SL; distinctly humped nuchal profile; 1 branched dorsal-fin ray; body dep...

Synopsis: Archerfishes (Toxotidae) are variously found in the fresh- and brackish-water environments of Asia Pacific and are well known for their ability to shoot water at terrestrial prey. These shots of water are intended to strike their prey and cause it to fall into the water for capture and consumption. While this behavior is well known, ther...

Siamese fighting (betta) fish are among the most popular and morphologically diverse pet fish, but the genetic bases of their domestication and phenotypic diversification are largely unknown. We assembled de novo the genome of a wild Betta splendens and whole-genome sequenced 98 individuals across five closely related species. We find evidence of b...

The South Java Deep-Sea (SJADES) Biodiversity Expedition 2018 was conducted between Indonesia and Singapore with the aim to investigate the deep-sea biodiversity in southern Java, Indonesia, in the eastern Indian Ocean. Examination of the fishes collected during the survey revealed 222 distinct taxa in 62 families. Of these, 54 species are known, t...

The genus Hypergastromyzon is revised based on fresh topotypic specimens and two other locations in Borneo. Hypergastromyzon humilis is redescribed, along with descriptions of H. abditus, new species, from upper Katingan basin; and H. sambas, new species, from upper Sambas basin. A new genus, Engkaria, is erected to accommodate H. eubranchus. Engka...

Barbodes pyrpholeos, new species, is the first cave-dwelling cyprinid fish reported from the Philippines. It is described from karst systems in Mindanao. It is distinguished from other congeners by having a poorly pigmented body with reddish fins in combination with a smooth dorsal-fin spine without serrations, and several additional morphological...

Parascolopsis rufomaculata was originally described from the NorthWest Shelf, Australia, by B.C. Russell in 1986. After examination of a single Parascolopsis specimen collected during the South Java Deep-Sea (SJADES) Biodiversity Expedition 2018, we report its presence in Indonesian waters, Eastern Indian Ocean for the first time. This new record e...

A total of 48 fish species from 24 families were recorded in the present survey. Of these 48 species, fourteen (14) species were endemic to Borneo (Anguilla borneensis, Barbodes sealei, ematabramis everetti, Rasbora cf. hubbsi, R. pycnope a, R. cf. semilineata, heriodes sandakanensis, emibagrus baramensis, eosthetus geminus, acrognathus keithi, Bet...

Siamese fighting fish, commonly known as betta, are among the world’s most popular and morphologically diverse pet fish, but the genetic processes leading to their domestication and phenotypic diversification are largely unknown. We assembled de novo the genome of a wild Betta splendens and whole-genome sequenced multiple individuals across five sp...

Southeast Asia is one of the world’s biodiversity hotspots, and the high level of diversity and endemism was reached by colonisation events as well as internal diversification. We investigate the phylogenetic relationships and biogeographic history of the loach genus Nemacheilus, which is widely distributed and common across freshwaters of Southeas...

Studies have shown that food chain length is governed by interactions between species richness, ecosystem size and resource availability. While redundant trophic links may buffer impacts of species loss on food chain length, higher extinction risks associated with predators may result in bottom‐heavy food webs with shorter food chains. The lack of...

The rules underlying the structure of antigen receptor repertoires are not yet fully defined, despite their enormous importance for the understanding of adaptive immunity. With current technology, the large antigen receptor repertoires of mice and humans cannot be comprehensively studied. To circumvent the problems associated with incomplete sampli...

Aim Ecological niche models (ENMs) are widely used to address urgent real‐world problems such as climate change effects or invasive species; however, the generality of models when projected through space and/or time, that is transferability, remains a key challenge. Here, we explored the effects of complex predictors and feature selection on ENM tr...

Betta nuluhon, new species, is described from a hill stream habitat in western Sabah. This species is allied to both B. chini and B. balunga, and differs from rest of its congeners in the B. akarensis group in having the following combination of characters: yellow iris when live; mature males with greenish-blue iridescence on opercle when live; mat...

A new species of Macrognathus of the M. aculeatus species group is described from the Kahayan River drainage in southern Borneo, Kalimantan Tengah, Indonesia. Macrognathus kris, new species, is distinguished from all Asian congeners in having the following unique combination of characters: rim of anterior nostril with two fimbriae and two fimbrules...

The cover image is based on the Original Article Morphological traits mediate fish occurrences in oil palm‐impacted tropical streams by Kenny W. J. Chua et al., https://doi.org/10.1111/fwb.13500.

Trigonostigma truncata, new species, is described from the coastal swamp forests along the east coast of the Malay Peninsula. It differs from all congeners, in having a gently sloping lateral head and nape shape, the characteristic black triangular marking, newly termed here as the axine, which is large with its caudal apex not reaching caudal-fin...

Recommended conservation actions to follow up on the IUCN Red List review workshop for freshwater fishes of Sundaland held in early 2019.

A total of 123 species of non-native freshwater fish, including seven possible hybrids, are recorded from the inland waters in Singapore. The majority (84 species, 68.3%) are from four families: Cyprinidae (37 species, 30.1%), Cichlidae (30 species, 24.4%), Osphronemidae (9 species, 7.3%), and Poeciliidae (8 species, 6.5%). Of these, 42 species-mai...

Land‐use change is a leading driver of biodiversity loss, especially in tropical fresh waters where the conversion of natural forest to monoculture plantations impacts freshwater fish assemblages. The environmental pathways underpinning shifts in fish assemblages, however, are poorly understood, but could potentially be inferred from trait–environm...

The new serranid fish Chelidoperca flavolineata is described on the basis of 22 specimens from Indonesia (southern coast of Java, eastern Indian Ocean), in depths of 115–210 m. Literature records indicate that the species also occurs off northern Australia. The new species is most similar to Chelidoperca investigatoris (Alcock 1890) (known from the...

The collision of the Indian and Eurasian landmasses in the Cenozoic was a decisive factor in shaping biodiversity patterns in Southern and Southeastern Asia. While most studies thus far have focused on the biotic interchange between India and Eurasia and evolutionary diversification on or around the Tibetan Plateau, little attention has been paid t...

Southeast Asian apple snails, Pila spp., have been declining since the introduction of globally invasive, confamilial South American Pomacea spp., yet Pila ecology remains poorly studied, with most occurrence records unconfirmed. Pila scutata, a previously widespread species, presumed native to the Malay peninsula and assessed as Least Concern in t...

Biodiversity-rich forests in tropical Southeast Asia are being extensively logged and converted to oil palm monocultures. In addition, extreme climatic events such as droughts are becoming more common. Land-use change and extreme climatic events are thought to have synergistic impacts on aquatic biodiversity, but few studies have directly tested th...

Fishes are a speciose and ecologically important group within severely threatened or impacted freshwater habitats of Sundaland, whose contributions to ecosystem functioning can be inferred from their functional diversity. However, there is limited understanding of the potential impacts of anthropogenic species loss on ich-thyofaunal functional dive...

The poorly known butid gudgeon Pogoneleotris heterolepis is redescribed based on 15 specimens obtained from fish markets and local fishers from 1982 to 2018, plus examination of the holotype. It is unique among butids in having a longitudinal papilla pattern and the preopercular canal continuous with the oculoscapular canal and is one of only two g...

• Freshwater swamp forests are poorly studied but highly threatened freshwater habitats, especially in Southeast Asia. Very little is known about the environmental factors associated with the assembly and spatial distribution of fish communities in these acid‐water habitats, although such knowledge is of immense importance for conservation and mana...

A new species of bagrid catfish in the genus Leiocassis is described from blackwater habitats in south central Borneo, central and southern Sumatra. Leiocassis bekantan, new species, can be distinguished from congeners in having a more produced snout with a longer preoral region when viewed ventrally, short extensions of the outermost principal cau...

• Freshwater fish are a vital resource for local communities across the rural tropics. In Southeast Asia, biodiversity‐rich forests are being logged and converted to extensive oil palm monocultures. This clearly has impacts on associated freshwater ecosystems, but the impact on their biodiversity remains largely understudied and poorly understood,...

Abstract. A new species of Betta from the B. waseri group is described based on museum material, and is very likely near extinction in the wild. It is most similar to B. hipposideros but differs from it in having a different throat pattern in which the black markings on the lower jaw are continuous with two black downward curved bars on the anterio...

Global biodiversity is being lost due to extensive anthropogenic land cover change. In Southeast Asia, biodiversity rich forests are being extensively logged and converted to oil-palm monocultures. The impacts of this land-use change on freshwater ecosystems, and particularly on freshwater biodiversity, remain largely under-studied and poorly under...

Fresh waters are increasingly threatened by flow modification. Knowledge about the impacts of flow modification is incomplete, especially in the tropics where ecological studies are only starting to emerge in recent years. Using presence/absence data dated approximately four decades apart (~1966 to ~2010) from 10 tropical rivers, we assessed the ch...

Studies of ecosystem functions are gaining traction in the scientific community along with a growing consensus that losses in ecosystem functions have widespread consequences. Food webs, which are networks comprising all trophic interactions (represented by links) between taxa present in a community (represented by nodes), are important aspects of...

Lobocheilos aurolineatus, new species, is described from the Mahakam River basin in East Kalimantan, Indonesian Borneo. It is distinguished from all other species of Lobocheilos except for L. ixocheilos and L. tenura in having one pair of barbels (maxillary) and by the presence of a broad, black midlateral stripe, approximately ¾ scale height in th...

The Nee Soon stream drainage in the Central Catchment Nature Reserve is virtually the last remaining fragment of primary freshwater swamp forest in Singapore. The forest type has been poorly studied in the Southeast Asia. The hydrology, water quality, as well as aquatic flora and fauna all have great theoretical and practical significance. The ecol...

The world’s smallest fishes belong to the genus Paedocypris. These miniature fishes are endemic to an extreme habitat: the peat swamp forests in Southeast Asia, characterized by highly acidic blackwater. This threatened habitat is home to a large array of fishes, including a number of miniaturized but also developmentally truncated species. Especia...

The freshwater fish diversity of Brunei Darussalam is reviewed. At present, a total of 104 species of freshwater fishes from 59 genera, 24 families and 10 orders is recorded. Eight species including one introduced species and two from brackish waters present new records for Brunei. The family Cyprinidae has the highest diversity with 40 species. Fo...

Snakehead fishes of the family Channidae are predatory freshwater teleosts from Africa and Asia comprising 38 valid species. Snakeheads are important food fishes (aquaculture, live food trade) and have been introduced widely with several species becoming highly invasive. A channid barcode library was recently assembled by Serrao and co-workers to b...

50% Majority rule consensus tree of the neighbour joining tree based on HKY distances. Bootstrap values from 1000 pseudoreplicates are shown. (EPS)

Snakehead chronogram from the BEAST analysis using a coalescence prior. Species delimitations based on BIN, GMYC single, GMYC multiple, and PTP thresholds are indicated by black bars. Misidentified and incomplete identified specimens are indicated with a red dot. (EPS)

Neigbour joining tree of Parachanna including additional sequences. The lineage corresponding to the new species Pa. sp. DRCongo is highlighted in light red. (PDF)

Neigbour joining tree based on HKY distance. Misidentified and incomplete identified specimens are indicated with a red dot. (EPS)

Maximum likelihood tree of the 423 taxa data set that only included unique haplotypes. Bootstrap values from 1000 pseudoreplicates are shown. (PDF)

Table of specimens, GenBank accession numbers, BOLD identification, BIN assignment and locality information. (XLSX)

Result of the bGMYC analysis showing sequence-by-sequence distribution of posterior probabilities. The coloured table is a matrix with the probabilities of sequences to be conspecific, ranking from yellow to red: the highest to the lowest values. The timetree corresponds to the consensus tree from BEAST analysis. (EPS)

The complex climatic and geological history of Southeast Asia has shaped this region’s high biodiversity. In particular, sea level fluctuations associated with repeated glacial cycles during the Pleistocene both facilitated, and limited, connectivity between populations. In this study, we used data from two mitochondrial and three anonymous nuclear...

Phylogeographic diffusion model. Map of SE Asia visualising dispersal timings of Aplocheilus panchax using molecular dating from the time calibrated mitochondrial tree (see Fig 2 in main text): a) 3.39Ma, b) 173,486ka, c) 114,987ka and d) 27,237ka. Black shaded areas indicate the confidence surrounding the ancestral locations, whilst blue shaded ar...

Median-joining nuclear allele networks based on geographic distribution. Median-joining nuclear allele networks for Aplocheilus panchax for three anonymous nuclear markers: a) AP44, b) AP50, and c) AP70. Colours correspond to geographic location, node size is proportional to allele frequency and numbers indicate the number of mutations. (PDF)

Sample information. Details of samples, sequences and corresponding GenBank Accession numbers for Aplocheilus panchax. Co-ords indicate whether sample locations were determined by GPS or GoogleEarth (GE). The exact locality of L6936 is unknown but originated in Kalkotta. (PDF)

Hox genes play a fundamental role in regulating the embryonic development of all animals. Manipulation of these transcription factors in model organisms has unraveled key aspects of evolution, like the transition from fin to limb. However, by virtue of their fundamental role and pleiotropic effects, simultaneous knockouts of several of these genes...

Community level ecological traits are thought to affect invasibility as more diverse communities with complex trophic interactions may be associated with greater biotic resistance. Elucidation of the nature of this relationship is often hampered by difficulties in characterising food webs, particularly where field data are lacking. We attempted to...

Aquatic macroinvertebrates and lower vertebrates were surveyed from the last remaining freshwater swamp forest in Singapore. Ecological data was collated from three years of field work. This book is a guide to the macroinvertebrates and the fish of the Nee Soon Swamp Forest, with identification keys provided as well.

After decades of absence, the smooth-coated otter Lutrogale perspicillata (Geoffroy, 1826) is now widespread along the northern shores of Singapore. Their diet was examined at four sites along the northern coast, through an analysis of 181 spraint samples, which revealed a diet mostly of fish (92%) and prawns (8%). Dietary composition differed amon...

The ornamental pet trade is often considered a key culprit for conservation problems such as the introduction of invasive species (including infectious diseases) and overharvesting of rare species. Here, we present the first assessment of the biodiversity of freshwater molluscs in the ornamental pet trade in Singapore, one of the most important glo...

Sources of ornamental freshwater molluscs (local ornamental pet retail shops and major ornamental exporters) (DOCX)

GenBank and BOLD Accession Numbers for COI and 16S sequences of freshwater molluscs of the ornamental pet trade. (DOCX)

River damming and other anthropogenic disturbances of natural habitats are among the main drivers of species loss through a range of direct and indirect effects. While the effects of river damming on aquatic species are relatively well studied, particularly with regard to their impacts on diadromous species and stenotopic riverine specialists, ther...

Sixty-two species of inland fishes are recorded from Pulau Tioman, Malaysia, representing an increase of 14 species (29%) since the last published checklist in 1999. Nine native species are recorded for the first time, viz., Neotrygon kuhlii (Dasyatidae), Chanos chanos (Chanidae), Lates calcarifer (Latidae), Selaroides leptolepis (Carangidae), Krae...

A fresh hairy-nosed otter roadkill was encountered along the Tanjung Malim-Sungei Besar Road in northern Selangor (Malaysia) in 2005. This appears to be the first fresh record of this elusive species from Selangor since 1929.

We record the presence of 435 fish species from the Eastern Johor Strait based on our fieldwork, a review of the existing literature, and an examination of photographs and museum specimens. Four species are recorded for the first time from the waters of Singapore: Pseudorhombus elevatus (Paralichthyidae), Heteromycteris hartzfeldii (Soleidae), Nuch...

The taxonomy of the rarely reported and poorly known arboreal sesarmid crab Labuanium politum (De Man, 1887), which is the type species of Labuanium Serène & Soh, 1970, is clarified. The species is an obligate associate of the mangrove nipah palm (Arecaceae: Nypa fruticans), hiding at the frond base during the day and feeding on the leaves at night...

Abstract. Exotic species—especially predators—are a potential threat to native species communities and ecosystems worldwide. Introduced exotic species may cause changes in anti-predator behaviour of prey species, thus affecting prey individuals’ time allocations for other crucial behaviours such as feeding and locating mates. To test this hypothesi...

Stiphodon multisquamus Wu & Ni, 1986 is a sicydiine goby species previously considered to be endemic to Hainan Island, in southern China. Recently, it was also recorded from the southern Chinese mainland and southern Japan, but it is rare in all of these localities. Available morphological data for S. multisquamus is derived from a small number of...

Anthropogenic land-cover change is driving biodiversity loss worldwide. At the epicenter of this crisis lies Southeast Asia, where biodiversity-rich forests are being converted to oil-palm monocultures. As demand for palm oil increases, there is an urgent need to find strategies that maintain biodiversity in plantations. Previous studies found that...

This present series of scientific exploration and expeditions was carried out from 2010 to 2012, totalling six and two weeks, and covering 153 and 50 field stations (some repeated) in Christmas Island and Cocos (Keeling) Islands respectively. The expeditions were carried out by a principle team of 11 from Singapore, with participants from Australia...

A distinctively patterned dwarf reef goby of the genus Trimma was obtained from submarine cave habitat in Christmas Island from expeditions conducted in 2010 to 2012. A comparison with valid Trimma species revealed this species to be conspecific with T. fasciatum, a recently described species from Palau, Saipan and Ryukyu islands. This current reco...

Christmas Island is one of the most isolated places in the Indian Ocean, and one of the truly significant natural heritage sites on Earth. Its most famous denizen, the Red Crab (Gecarcoidea natalis), is world-renowned for its mass spawning, and this has been declared one of the 10 most amazing natural phenomena on Earth. With its large number of en...

This present series of scientific exploration and expeditions was carried out from 2010 to 2012, totalling six and two weeks, and covering 153 and 50 field stations (some repeated) in Christmas Island and Cocos (Keeling) Islands respectively. The expeditions were carried out by a principle team of 11 from Singapore, with participants from Australia...

We report on opportunistic sampling and/or observations of the fauna of five submarine and six associated anchialine caves in Christmas Island conducted over a total of five weeks from 2010 to 2012. The surveys were conducted mainly via hand picking, overturning of coral rubble, baited fish traps (using baitfish and fish food pellets) and with the...

The South American cichlid fish, Acarichthys heckelii, is one of many exotic species established in Singapore’s artificial freshwater habitat; forming the only recorded population outside its native distribution. The discovery of an A. heckelii individual in a sensitive natural waterway (Nee Soon Swamp Forest) prompted this study, which aimed to in...