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Fishes of the Mekong- how many species are there?

4Catch and Culture Volume 15, No. 2 August 2009
Recent records suggest that about
850 ‘freshwater’ fish species occur in
the basin, but many more marine and
coastal fishes may at times enter the
waters of the Mekong delta
Loss of biodiversity is a major concern for biologists,
who warn that we are now well into ‘the century of
extinctions’ during which conservation biology is likely
to become an increasingly important discipline (Dubois
2003). While there is increasing understanding of the
need to manage habitat to maintain biodiversity, there
is much less awareness that rational management of
ecosystems faces a major ‘taxonomic impediment’,
the incompleteness and inaccuracy of inventories
of biodiversity, which are the starting point for any
conservation program .
Tropical rivers are generally among the most diverse
ecosystems and their biodiversity is particularly
threatened by habitat changes and introduction
of exotic species (Coates et al. 2003, Dudgeon et
al. 2006). The Mekong system is thought to be an
international ‘hotspot’ of unusually high biodiversity,
so there is an urgent need for an up-to-date inventory
of the system’s biodiversity, both in an absolute sense
and relative to other larger tropical rivers, as well as
accurate information on individual species’ distribution
and migration patterns.
One element of biodiversity is species richness,
an easily understood notion and one that is useful
richness of the Mekong system is a topic of particular
Fishes of the Mekong–howmany
speciesare there?
peoples and the claim by many authors that the
system has unusually high biodiversity.
It should also be noted that apart from species
richness (the subject of this article), other features of
biodiversity ensure that the Mekong deserves the title
of a biodiversity hotspot and should be given a high
priority in conservation. These include the apparently
rural populations (Hortle 2009).
The biological species concept (BSC) has been
generally accepted by zoologists as the most useful
potentially reproductively isolated’ population(s)
of organisms (de Queiroz 2005)1.The BSC can be
seen as a special case of the broader ‘evolutionary
species concept’, which covers asexually reproducing
species as a separately evolving lineage (Wiley 1978).
Although there is a lively and ongoing debate about
Hey 2006), in practical terms testing for reproductive
isolation is usually not feasible, and genetic studies to
reveal phylogeny (evolutionary relatedness) are too
expensive to be applied to the many wild populations
and to diagnose ‘species’ taxonomists continue to
number of gill rakers, number of scales, counts of
1An alternative ‘phylogenetic’ system based only upon degree of genetic relationship has been developed recently and is being increasingly used in
cladistics (Rieppel 2006).
Naturae, with rules now formalised in the Code set by the International Commission on Zoological Nomenclature (
By Kent G. Hortle *
August 2009 Catch and Culture Volume 15, No. 2
nraysorevenshapeandcoloration2. Taxonomists
found of intermediates between what were thought to
be reproductively isolated populations, or if genetic
studies indicate the presence of sympatric but
reproductively isolated populations of morphologically
to study in the Earth’s biodiversity in detail, and
differences in opinion between taxonomists, ensure
been described on morphological grounds are likely to
continue for the foreseeable future.
The number of species recorded from any particular
system tends to increase as species are collected
new species are found and described, with the rate
of addition of species tending to decrease over time
to an asymptote. Figure 1 suggests that there are
from the Mekong catchment, as is also evident from
listings of un-described species in recent literature
(see below). However, this is not an unusual situation
for tropical river systems, indeed it seems likely that
the Mekong has by now received comparable or more
attention than many other large tropical river systems
which are less accessible or subject to security risks.
It is also highly likely that in many other tropical river
species introductions may have caused the extinction
This inference can be reasonably drawn based on the
situation in well-studied regions: for example in North
species are considered imperilled (Jelks et al. 2008).
As well as possible artefacts introduced by differences
in taxonomic effort, comparisons between systems
should take account of other factors which are
for example, the ecoregion in which the system is
situated (Abell 2008), the fact that tropical systems are
generally richer in species than temperate systems,
and the ‘species-area effect’: more species are found
in larger areas, other factors being equal. Welcomme
(1985 Fig 5.1) used data from 47 major rivers to show
size of the river catchment, one indicator of available
habitat area. Lévêque et al. (2008) provide updated
graphs of the relationship between the size of some
major river systems and their species richness, and
de Silva et al. (2007 Fig 1.) show that land area alone
accounts for over 70% of the variance in published
and southeast Asia. It is to be expected therefore
that the Mekong will support more species than other
smaller tropical river systems in the Oriental region
because of the large extent of available aquatic habitat
within its catchment of about 800,000 km2.
the boundary geographically as a line across the
mouth, but a more useful ecological boundary would
be based on salinity. In the dry season, saline water
extends at least 60 km inland, whereas in the wet
season a surface layer of fresh water extends several
kilometres offshore in the river’s plume. Although not
well-documented for the Mekong, it can be assumed
that the downstream limit of distribution of strictly
freshwater species, as well as the penetration of
marine species into the estuary changes with season.
salinity so they are also likely to move seasonally.
Any reference to species counts of the system should
normally found in brackish or marine waters that
may only be present in the ‘Mekong’ seasonally or
Published estimates of the number of species in the
Mekong system appear to have increased rapidly in
the last few years, as can be seen from the following
brief chronology:
• Taki(1978)reviewedinformationuptotheearly
1970s and estimated that there were about 300
species known from the lower Mekong basin.
• Welcomme(1985Fig5.1)estimatedthatthere
were about 600 species in the Mekong, and
ranked the system third in terms of its species
richness after the Amazon and the Zaire, both of
which are larger rivers.
6Catch and Culture Volume 15, No. 2 August 2009
• Rainboth(1996)recorded475speciesfrom
Cambodia and estimated that the Mekong “has
this estimate in an interview (Jensen 1996). This
estimate however was clearly his expectation
of the total that might be eventually found after
more collection and taxonomic work.
• Kottelat(2001p19)statedthattherewere
documented records of about 700 species from
the Mekong basin, and because there were
suggested that they should not be quoted.
Several authors provided similarly high but
of species actually recorded or a minimum estimate.
In some cases, authors implied that the species count
was for the river, when many species are found only
in upland tributaries or in the estuary or in specialised
habitats such as lakes or caves. Some of these recent
species estimates include the following.
• ‘Thereare1200recordedshspecies’
(Sverdrup-Jensen 2002).
• ‘It(theMekong)isahotspotforbiodiversitywith
between 1200 and 1600 described species of
• ‘Thereareatleast1200andpossiblyasmany
Basin’ (Coates et al. 2003).
• ‘Therearemorethan1200speciesintheriver’
(sic) (MRC 2003).
compendium of species of the Mekong, the Mekong
Fish Database (MFD), in 2003 and widely distributed it
as 24 introduced species that were recorded from or
thought likely to be present in the lower Mekong basin
to their known occurrence in water of different
salinities, using information which has been obtained
from FishBase (Froese and Pauly 2009).
Freshwater only : 539 species
Freshwater-brackish: 79 species
Fresh- brackish marine: 113 species
Brackish only: 4 species
Brackish and marine: 115 species
Marine: 48 species
The marine species and many of the brackish/marine
species have only been recorded from the sea off the
mouth of the Mekong or from nearby marine waters,
and records for several of the freshwater species are
questionable, so the MFD supports an estimate of
about 750 species likely to be found at times within
freshwaters of the system, which can be loosely
consistent with Kottelat’s estimate, nevertheless higher
unsubstantiated estimates continued to be published,
for example:
• ‘Thenumberofshspeciesisatleast1200’
(Mattson 2004)
• ‘Thenumberofshspeciesthathasbeen
found in the (Mekong basin) exceeds 2000’ (van
Zalinge et al. 2004).
The citation of species numbers seems to represent
that supports a commonly-held belief (the Mekong has
‘high’ biodiversity) while ignoring the actual counts of
species from the system published by Kottelat in 2001
and in the MFD in 2003. The variability between recent
published estimates of species richness certainly
creates a credibility issue for those seeking to promote
conservation of the system’s biodiversity, as well as
have a long history of evolution in freshwaters, and if this approach were used the total for the Mekong system would fall to about 530 species
Distribution. Academic Press: San Diego, USA.
August 2009 Catch and Culture Volume 15, No. 2
Figure 1: TheSundashelf
Showing the maximum extent of sea level regression over the last 250,000 years, the -120 m
contour. Based on (Voris 2000)
Figure 2: SpeciesdescribedfromtheMekongRiversystem
8Catch and Culture Volume 15, No. 2 August 2009
Sisterspecies Reviseddistributionsummary
Amblyrhynchichthys truncatus (Bleeker, 1851) Malay Peninsula and Borneo
Amblyrhynchichthys micracanthus Ng&Kottelat,2004 LowerandMiddleMekongtoVientiane,ChaoPhraya,MaeKhlong,Tapi
Bagrichthys macracanthus (Bleeker, 1854) Sumatra, Peninsular Malaysia, northern Borneo (Sarawak)
Bagrichthys majusculus Ng,2002 LowerandmiddleMekongRiversystem
Balantiocheilos melanopterus (Bleeker, 1851) Kalimantan, Malay Peninsula, Sumatra
Balantiocheilos ambusticauda Ng&Kottelat,2007 LowerandmiddleMekongupstreamtoNamNgum,ChaoPhraya
Hemiarius stormii (Bleeker, 1858) Eastern Malay Peninsula and west Borneo
Hemiarius verrucosus (Ng,2003) LowerMekongtoKhoneFallsandpossiblyBangPakongR.,Southeast
Kryptopterus cryptopterus (Bleeker, 1851) Borneo, Java, Sumatra and Malay Peninsula
Kryptopterus geminusNg, 2003 LowerandmiddleMekong,MaeKhlong,BangPakongR.,ChaoPhraya
Kryptopterus schilbeides (Bleeker, 1858) Eastern Sumatra and western and southern Borneo
Kryptopterus paraschilbeidesNg,2003 LowerandmiddleMekongupstreamtoVientiane
Ompok hypophthalmus (Fang & Chaux, 1949) Java and southern Borneo (Barito River drainage)
Ompok urbaini Ng,2003 Mekong,ChaoPhrayaandPasakRiverdrainages
Ompok rhadinurus Ng, 2003 Sumatra, the Malay Peninsula and Borneo
Ompok eugeneiatus (Vaillant, 1893) Peninsular Malaysia, central Sumatra and western Borneo
Ompok pinnatusNg,2003 LowerMekongRiverandChaoPhrayadrainages
Pangasius kunyit Pouyaud Teugels & Legendre, 1999 Sumatra and Kalimantan (southern Borneo)
Pangasius mekongensis Gustiano, Teugels&Pouyaud,2003 LowerMekongRiversystem
Pangasius sabahensis Gustiano, Teugels & Pouyaud, 2003 Sabah, northern Borneo
Pangasius polyuranodon Bleeker, 1852 Sumatra and Borneo
Pangasius elongatus Pouyaud,Gustiano&Teugels,2002 ChaoPhraya,MekongandBangPakongbasins
Pangasius mahakamensis Pouyaud, Gustiano & Teugels, 2002 Mahakam River, East Kalimantan, Borneo
Polynemus dubius Bleeker, 1853 Malay Peninsula, Sumatra, Kalimantan
Polynemus aquilonaris* Motomura,2003 ChaoPhrayaandMekongRiverbasins
Wallago leerii Bleeker, 1851 Southern Thailand, Malay Peninsula and western Indonesia
Wallago micropogon Ng,2004 LowerandmiddleMekongtoLuangPhabang,andmiddleChaoPhraya
* alsoincludesmaterialformerlyidentiedas Polynemus longipectoralis
The newly described Mekong species is shown in bold after the species which was formerly considered to occupy a large range on both sides of the
Sunda shelf, including the Mekong system
August 2009 Catch and Culture Volume 15, No. 2
Since the MFD was published there has been
considerable taxonomic work which has resulted in
• ‘Splitting’ofspecies:inatleast12casesa
species that was considered widespread in
rivers that formerly ran across the Sunda shelf
has been ‘split’ into ‘sister’ species, a mainland
Indochinese (including Mekong) species and
one or more ‘Sundaic’ species, found in river
systems to the south (Figure 2, Table 1). Such
splitting does not change the species count
for the Mekong, only the name applied to the
Mekong species. But it can cause confusion
and double-counting when distribution records
for the Sundaic species are not updated,
which is a problem for example in the current
version of FishBase. Examples of split species
are shown in Table 1 with updated distribution
• Descriptionofnewspecies:newspeciesare
still being described, either from new collections
or when taxonomists re-examine existing
collections which may have been stored in
museums for many years. At least 16 new inland
species have been described from the Mekong
River system since the MFD was published in
2003 (Table2), adding to the species count for
the system.
• ‘Lumping’:twoormorespeciesformerlythought
to be distinct are synonymised when additional
examination shows that there is overlap in
the range of variation of diagnostic characters
between populations that have been named
as separate species, or when it is found that
a species has been named more than once.
Since 2003 ‘lumping’ of species has reduced
the count for the Mekong system by about 20
species, more than compensating for the effect
of description of new species.
• Revisionsofgroups:severalgroups(genera
or families) have been revised since the MFD
was published, with many new generic names
species. For example, the widespread genus
Botia, which includes several common Mekong
species, was split into seven genera by Kottelat
(2004), with Mekong species now falling within
three genera. Thus the red-tailed botia, formerly
Botia modesta is now known as Yasuhikotakia
Species Distributionsummary
Scizothorax nudiventris YangChen&Yang,2009 UpperMekong,Yunnan
Bangana brevirostris Liu & Zhou, 2009 UpperMekong,Yunnan
Mekongina lancangensis Yang,Chen&Yang,2008 UpperMekong,Yunnan
Minyclupeoides dentibranchialus Roberts, 2008 Lower Mekong, Cambodia
Oreoglanis jingdongensis Kong,Chen&Yang,2007 UpperMekong,Yunnan
Pareuchiloglanis abbreviatus Li,Zhou,Thomson,Zhang&Yang,2007 UpperMekong,Yunnan
Pareuchiloglanis prolixdorsalis Li,Zhou,Thomson,Zhang&Yang,2007 UpperMekong,Yunnan
Tonlesapia tsukawakii Motomura & Mukai, 2006 Great Lake, Tonlé Sap drainage in Cambodia.
Polynemus bidentatus Motomura & Tsuwaki, 2006 Mekong delta, Viet Nam
Pseudobagarius lifer (Ng & Rainboth, 2005) Tonlé Sap drainage near Phnom Penh, Cambodia
Pseudobagarius nitidus (Ng & Rainboth, 2005) Mekong River downstream of Khone Falls near Cambodia-Lao border
Akysis fuliginatus Ng & Rainboth, 2005 Lower Mekong River in northern Cambodia
Betta stiktos Tan & Ng, 2005 Mekong Drainage, Cambodia
Schistura bannaensis Chen,Yang&Qi,2005 UpperMekong,Yunnan
Oreoglanis macronemus Ng, 2004 Xieng Khouang, Lao PDR
Hemimyzon ecdyonuroides Freyhof & Herder, 2002 Headwaters of Se San River, Viet Nam
10 Catch and Culture Volume 15, No. 2 August 2009
has also led to many new names for genera
(Marceniuk and Menezes 2007). Such name
changes are relatively easy to follow by updating
species lists using FishBase and do not affect
the species count for the system.
• Additionaldistributionrecords:speciesthat
are already described from elsewhere are
the Mekong system. Such information has not
been updated in any systematic way since
the MFD was published. Summary distribution
records are often woefully inadequate for
assessing whether it is likely that a species
is present in the area of interest, in some
cases simply reading “Asia”, while original
locality data on museum specimens are often
published in ecological surveys typically include
as ‘sp1’, ‘sp2’ etc.) or may contain errors (for
example non-Mekong species), hardly surprising
correctly. Ideally, distribution data for inland
species in FishBase would accurately identify
the major river basins in which each species
task to check and carefully summarize and
update such information. A review and cross-
checking of Mekong system species listed in
Baird et al. (1999), Kang et al. (2009), Kottelat
(2001), Rainboth (1996) and Vidthayanon
(2008) suggests that there are about 100
additional species that have been recorded
from freshwaters of the Mekong basin, although
most of these are not formally described or are
of uncertain taxonomic status. Therefore it is
reasonable to estimate that there are about 850
‘freshwater’ species known from the system.
which enter fresh water for short periods, or marine
species which may cross the geographical boundary (a
line across the mouth) during dry periods. Systematic
delta region would do much to remove the uncertainty
in species counts and resolve the discrepancies in
published estimates. If marine and coastal ‘visitors’ are
included, there are about 1100 species recorded from
or thought likely to occur in the system at times based
on their occurrence in the Mekong’s plume. More
species will continue to be found, but at present there
are no grounds for quoting higher estimates.
The available data indicate that there are about 850
(a total that includes some undescribed species of
uncertain status) , with a total estimate of about 1100
if the possible coastal or marine visitors are included.
As mentioned above, comparison with other river
systems should take into account the biogeographic
province or ecoregion, the area of each system, the
relative taxonomic effort that has been applied, and the
extent to which biodiversity may have been lost before
it could be documented. If it is evident that the Mekong
does indeed have more species than expected for a
river of its size and location, it would be of interest to
explore the possible causes, which might include its
recent geological history and the geography of the
Unless great care is taken, comparisons with other
river systems may lead to erroneous conclusions.
For example, according to FishBase there are 405
species recorded from the Zaire (Congo) and 1212
species recorded from the Amazon, but these are
clearly under-estimates, both because existing records
have not been systematically compiled and because
many species remain to be described. Roberts
but Lévêque et al. (2008) cautioned that existing
information for this basin needs to be synthesised
and that many new discoveries are anticipated. For
the Amazon, Tedesco et al. (2005) used an estimate
of 1761 species and Lévêque et al. (2008) recorded
2416 species, but Kottelat (2001) cited an opinion
that the number of species in South America could
more than double with new collections and taxonomic
effort. The Amazon’s catchment is about seven times
it is impossible to know whether any of these large
river system’s species richness is above or below
the average that would be predicted for large tropical
rivers of their size.
August 2009 Catch and Culture Volume 15, No. 2
The Water Studies Centre of Monash University kindly
the preparation of this paper. I thank Eamonn Hortle
for assisting with compilation of species information
from FishBase and Chris Burridge and Chris Barlow
for helpful comments on a draft manuscript.
*Mr Hortle was a technical ofcer at the MRC Fisheries Programme
from 2001 to 2005 and currently works as a consultant on sheries
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Systematic Zoology 27, 17-26.
... Actualmente la biodiversidad de los ecosistemas de agua dulce se encuentra amenazada en todo el mundo, enfrentando presiones por las actividades antropogénicas que se incrementan cada vez más, disminuyendo la biodiversidad (Cooke et al., 2012;Darwall & Freyhof, 2015;Hortle, 2009). Sumado a esto, el cambio climático podría aumentar estas amenazas a través de la extinción directa de las especies y de los cambios progresivos en la estructura, fisiología y composición, debido a los cambios en las áreas de distribución, tras un aumento de la temperatura del agua (Ficke et al., 2007;Oberdorff et al., 2015;Senior et al., 2019). ...
... Los ecosistemas dulceacuícolas se encuentran entre los más amenazados a nivel mundial (Cooke et al., 2012;Darwall & Freyhof, 2015;Hortle, 2009), especialmente en el neotrópico, donde, los hábitats de las especies se enfrentan a continuas amenazas (McMahan et al., 2020) y los impactos del cambio climático podrían ser más severos que en las regiones templadas (IPCC, 2022;Tewksbury et al., 2008). Además, se prevé que el cambio climático afecte la distribución de las especies, sin embargo, algunas podrían aumentar su área de distribución y otras disminuir (Yousefi et al., 2020), por lo tanto, las especies solo tendrán tres respuestas; adaptarse a las nuevas condiciones climáticas, migrar a hábitats adecuados o extinguirse (Oberdorff et al., 2015;Yousefi et al., 2020). ...
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The consequences of climate change on freshwater ecosystems and fish are evident, as their phenology and distribution have been altered. The objective of this study was to assess future climate change models as predictors of range reduction of two endemic cichlid species (Chortiheros wesseli and Amphilophus hogaboomorum) in Honduras. Bioclimatic and hydroclimatic variables and four modeling techniques were used: Maximum Entropy, Random Forest, MaxNet and Boosted Regression Trees. The best model was validated using the Area Under the Curve (AUC) and True Skill Statistics (TSS). The general circulation model HADGEM2_ES was used under the scenarios of Representative Concentration Pathways RCP4.5 and RCP8.5 at the 2050 and 2080 horizons. The projections show Random Forest as the best model and under the climate change scenarios the distribution of both species decreased from 17.94% to 57.02% for RCP4.5 and 19.19% to 69.48 for RCP8.5. Suitable protected areas will not maintain favorable conditions for C. wesseli and potential areas for A. hogaboomorum are not included in the Honduran protected areas system. These results have important implications for the conservation of two endemic freshwater cichlid species in Honduras.
... The Mekong basin is one of the richest sites of biodiversity in the world after the Amazon River basin which has the higher level of biodiversity [2]. Mekong is home to approximately 20,000 plant species, 430 mammals, 1,200 birds, 800 reptiles and amphibians [3], and around 850 freshwater fish species including the world largest freshwater fish [4]. Around 80% of the nearly 65 million people living in the Lower Mekong River Basin depend their lives on the river's natural resources [5]. ...
The assessment of flood dynamics is essential in supporting the nation and all stakeholders for the better flood management and adaptation. Climate change and hydropower dam operation pose threat to water resources in the Lower Mekong Delta. Cambodia is vulnerable to the flood impact due to its low adaptive capacity. Historically, flood has big impact on Cambodian society, economics and environment. This research was conducted by using the 2D HEC-RAS Modeling Application to study the flood dynamics under the influence of climate change, hydropower operation and irrigation expansion. The analysis is based on the observed flow and water level of 5 years from 2015 to 2019 and digital elevation model (6 m x6 m). The indices indicated satisfactory performance for the simulation model with the value of NSE between 0.78 and 0.97 and R2 between 0.80 and 0.96. The impact of climate change, hydropower operation and irrigation expansion, on the Cambodian Mekong floodplain area in forms of the flood inundation characteristics using the above well-configured hydraulic model framework. The results show that the flood extent increases around 74% in dry season and decrease around 20% in rainy season. Comparing to the baseline, the results of the scenario study suggest that the study area is likely to experience larger floodplain area in dry season (October to April), and flood extent in rainy season is lesser (May to October). The simulated results will provide important hydraulic information to respond to the future change of flood extent. The increase of water level in the dry season will provide water availability in the water supply sector and agriculture.
... Fisheries managers and scientists have updated info on fish diversity within the Mekong river delta [24,25]. The dominance of marine characterizes fish composition in the western estuaries originated species with Engraulidae and fish family being dominant. ...
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Vietnam, with a rich river system, many lagoons, and a long coastline, the fish fauna comprises both brackish and freshwater fish. The system of Mekong river is an extensive river located in the south of Vietnam. There are all kinds of brackish and freshwater fish in this river system. This chapter reveals data on the fish species composition and their roles in the Vietnamese Mekong delta. Moreover, the growth pattern and condition factor of some commercial fishes are also presented in this chapter. Their population structure and fishing status are also reported in this chapter.
... The Mekong River in Southeast Asia is one of the world's most productive and dynamic rivers, hosting an open-access wild capture fishery of over 1200 fish species (Poulsen et al., 2004). The basin's 60 million inhabitants rely on the river for food and income security, harvesting 2.1 million metric tons of fish per year at a retail value of up to $7.8 billion US per year (Hortle, 2009). Less than 30 years ago, the river (Fig. 5a) flowed freely for 4350 km (MRC 2016). ...
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This paper introduces PySedSim, an open-source, object-oriented, Python-based, daily time step river basin simulation screening model for flow, sediment, and hydropower in networks of reservoirs and river channels. The model enables users to explore representations of four key concerns relevant to the selection and evaluation of alternative reservoir configurations: 1) management approaches to improve the passage of sediment through and around reservoirs to avoid storage capacity loss and downstream ecological impacts; 2) search for flexible and adaptive reservoir operating policies designed to achieve multiple objectives; 3) alternative design features such as dam gates, which are necessary to enable ecologically-focused reservoir features; and 4) uncertainties associated with hydroclimatic drivers and sediment processes. PySedSim is intended to support deliberative decision-making and design processes. We highlight PySedSim's functionality by demonstrating its use in a real decision context focused on identifying siting, design, and operation alternatives for the proposed Sambor mega Dam in Cambodia. Software availability Name of Software: PySedSim Description: PySedSim is an open-source, object-oriented, Python-based daily time step river basin simulation model for flow, sediment, and hydropower production in networks of reservoirs and river channels. It is intended to predict in relative terms the spatial and temporal accumulation and depletion of sediment in river reaches and in reservoirs under different reservoir operating and sediment management policies. The model can be run in both stochastic (Monte Carlo) and deterministic modes. It also offers integrated support for coupling with an external evolutionary optimization algorithm to identify tradeoffs among operating policies designed to perform well across a suite of user-defined objectives.
... New species are being discovered, taxonomy is being revised, and estimates for species numbers vary depending on the inclusion or otherwise of estuarine fishes. Hortle (2009b) estimated there are at least 850 freshwater fishes in the Mekong. More recently, the Mekong River Commission's Fish Species Database lists 1,144 species, which includes marine visitors and estuarine fishes, in the river (MRC, 2020). ...
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Development of large scale hydropower is proceeding rapidly in the Mekong basin without adequate consideration of the severe and cumulative impacts the dams and reservoirs will, and are already beginning to, have on biodiversity, livelihoods and the economies of the lower Mekong countries. Migratory aquatic species will be particularly affected, and global experience indicates that fishways proposed for large mainstream and tributary dams will not provide effective amelioration. An offset strategy of remediating small weirs, flood control devices, regulators and irrigation works on tributaries and flood plains is more likely to be an effective and economically efficient means of supplementing fisheries to compensate for the negative impact of mainstream dams. Mainstream hydropower developments may result in future stranded assets, high electricity costs and even threaten the sovereignty of lower Mekong countries.
... The Mekong River Basin supports an estimate of 20,000 plant, 430 mammal, 1,200 bird, 800 reptile and amphibian species (Thompson 2008). It also supports an extraordinary number of fish species, which has been estimated at about 850 species and possibly more if including coastal or marine visitors (Hortle 2009). The river is home to some of the largest fish species in the world, such as the Mekong Giant Catfish (Pangasianodon gigas), which has a maximum recorded weight of 350 kilograms as well as a length up to three meters (FishBase, n.d.). ...
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In the midst of anthropogenic environmental change, local ecological knowledge (LEK) emerges as a valuable resource for communities to mitigate impacts and secure their livelihoods. This study broadens an understanding of LEK in environmental change literature to take into account the political and social implications of its usage and mobilization. It adopts the concept of agency to critically examine the role of LEK, the ways people interpret and negotiate environmental transformations, and the implications of those responses on human-river relations. This qualitative research is based on a case study of riparian (i.e., along river) communities in Chiang Khong and Wiang Kaen, Chiang Rai, Thailand. Data was collected via a combination of participant observation, semi-structured interviews, and document research, and analyzed using the qualitative content analysis (QCA) method. Findings show that while riverine transformations have sped up the shifting away from river-based livelihoods, LEK usage helps mediate or resist the reconfiguration of human-river relationship. The process of LEK hybridization underpins diverse strategies to cope with, adapt to, as well as resist against the ongoing Mekong River transformations. LEK serves as a source of personal agency and potential empowerment for local resource users, who have been marginalized by the process of development. Individual- and collective-oriented strategies also draw on social network to improve access to information or external support. Furthermore, LEK contributes to the exercise of political agency through place-based strategies of conservation and villager research projects. Its use as a political tool allows the multi-scale network of resource users, NGO workers, and academics to move beyond the local and mobilize their struggles at the regional and international levels.
... Из общего видового богатства ихтиофауны р. Меконг от 461 до 629 видов отмечены в дельте на территории Вьетнама [2,3,4,6,10,14,15,16]. Рыбы и -в меньшей степени -другие гидробионты являются важнейшими источниками белка животного происхождения, не только употребляемыми в пищу, но и обеспечивающими средства к существованию для населения нижнего Меконга -примерно для 60 млн людей, проживающих в Лаосе, Таиланде, Камбодже и Вьетнаме. ...
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2018 г. стандартным промысловым бимтра-лом от предустьевой морской зоны вверх по течению проток на расстояние до 110 км. Средняя масса улова-около 30 кг, максимальная-100 и более кг, однако средний уровень вылова рыб и ракообразных составлял 1,5 кг, наибольший-4 кг, а остальная часть приходилась на мусор и остатки растительности. Для сравнительного анализа пространственной изменчивости обилия рыб и десятиногих ракообразных на 36 станциях вычислены средние удельные показатели числен-ности и биомассы по результатам 102 тралений. Установлены весьма широкие пределы вариаций количественных показателей. Так, удельная численность рыб колебалась от 23,4 до 1978,2 (в сред-нем-333,3) экз.·га-1 , десятиногих ракообразных-от 10,6 до 5091,5 (358,1) экз.·га-1 , биомасса этих групп гидробионтов составляла 219,1-22773,5 (1969,9) г·га-1 и 31,4-9337,1 (740,6) г·га-1 со-ответственно. Выявлены основные закономерности пространственного распределения плотности гидробионтов. Отмечено увеличение средней удельной численности рыб в верхней части исследо-ванных водотоков до 656,2 экз.·га-1 , что вдвое превышает показатель в целом по дельте, при относи-тельно равномерном распределении средней удельной биомассы, связанном с присутствием моло-ди массовых промысловых видов и мелкоразмерных рыб. Тренды пространственного распределе-ния численности и биомассы десятиногих ракообразных весьма близки; наибольшие их показатели зарегистрированы в устьях рек и в приустьевой морской зоне дельты за счёт появления в соста-ве сообществ креветок подотряда Dendrobrachiata (пенеидные креветки) и представителей подот-ряда Pleocyemata (крабы). Среди рыб в меженный период доминировали представители морских по происхождению семейств: пальцепёрые (Polynemidae), ариевые сомы (Ariidae) и анчоусовые (Engraulidae), доля которых в общем вылове по относительной численности составляла 39,4, 20,4 и 13,4 % соответственно, по биомассе-28,5, 34,9 и 9,2 %, преимущественно за счёт эвригалин-ных эстуарных и прибрежных (шельфовых) видов. Среди десятиногих ракообразных преобладали морские креветки (семейства Penaeidae и Aristeidae) и пресноводные (семейство Palaemonidae). Представители семейства карповых (Cyprinidae) (одного из наиболее богатых по разнообразию, численности и биомассе в дельте р. Меконг), равно как и представители ряда других семейств пресноводных рыб, за исключением акизовых сомов (Akysidae), не характеризовались обилием, что связано с их миграциями в сухой сезон вверх по течению реки. Проанализировано влияние некоторых антропогенных факторов на количественные показатели донно-придонных сообществ. 14
... Из общего видового богатства ихтиофауны р. Меконг от 461 до 629 видов отмечены в дельте на территории Вьетнама [2,3,4,6,10,14,15,16]. Рыбы и -в меньшей степени -другие гидробионты являются важнейшими источниками белка животного происхождения, не только употребляемыми в пищу, но и обеспечивающими средства к существованию для населения нижнего Меконга -примерно для 60 млн людей, проживающих в Лаосе, Таиланде, Камбодже и Вьетнаме. ...
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The characteristics of the quantitative distribution of fish and decapod crustaceans of benthic and demersal communities were first studied in the six main channels of the Tien River in the lower part of the Mekong Delta, and the coastal zone adjacent to estuaries. The material was collected during the low water season from April to June 2018 using standard commercial beam trawl. The region from the estuary zone upstream to a distance of 110 km has been studied. The coordinates of the beginning and the end of the trawling were determined using a GPS navigator. The average weight of the catch was about 30 kg, the maximum was 100 kg and more. The average catch of fish and crustaceans was about 1.5 kg, the maximum was 4 kg; the anthropogenic wastes and remnants of vegetation made up the rest of the catch. The average specific amount and biomass values which were collected at 36 stations based on 102 trawling results were computed for a comparative analysis of the spatial variability of fish and decapods abundance. The presence of wide limits of variations in quantitative indicators was established. Specific number of fish varied from 23.4 to 1978.2 (average 333.3) specimens·ha-1, decapod crustaceans – from 10.6 to 5091.5 (358.1) specimens·ha-1, the biomass of these groups was 219.1–22773.5 (average 1969.9) g·ha-1 and 31.4–9337.1 (average 740.6) g·ha-1, respectively. The main regularities of the spatial distribution of the density of hydrobionts have been identified. The increase in the average specific abundance of fish in the upper part of the investigated watercourses to 656.2 specimens·ha-1 was noted, its value is twice higher than that of the whole areas along the delta, whereas the distribution of the average specific biomass was fairly uniform. These patterns were associated with the presence of juveniles of commercial species and small-sized fish species in the upper reaches of rivers. The trends in the spatial distribution of abundance and biomass of decapods were very close. The highest values were observed at the mouths of rivers and the estuary zone of the delta, as the shrimps of the suborder Dendrobrachiata and the crabs of the suborder Pleocyemata appeared in the communities. Among the fish, the representatives of the marine-originated families which belong to Polynemidae, Ariidae, and Engraulidae were dominant. Their share in catches was 39.4, 20.4 and 13.4 % in abundance and 28.5, 34.9 and 9.2 % in biomass, respectively. Euryhaline estuarine and coastal (shelf) species prevailed. Sea shrimps of the families Penaeidae, Aristeidae and freshwater prawn from the family Palaemonidae prevailed among the decapods. Representatives of the Cyprinidae family (the richest in terms of diversity, abundance and biomass in the Mekong Delta) and a number of other freshwater fish, with the exception of Akysidae, were insignificant in abundance, probably due to their migrations in dry season from upstream sections of the river. The influence of some anthropogenic factors on the quantitative indicators of benthic and demersal communities was analyzed. Large amounts of solid domestic and industrial waste, especially from towns, could be one reason for the relatively low average values of density of fish and decapods. This could have a negative impact on feeding and on the life cycles of these hydrobionts in general. Anomalies in the distribution of water salinity and the specific density of fish and crustaceans in the region of the dam on the river Balay were discovered. Upstream from the dam, the water was fresh, whereas, in downstream part, the salinity of the bottom water layer could reach 17 ‰. The average specific abundance of fish was higher in the lower reaches of the dam, and the average specific biomass was higher in the upper dam. The low average specific abundance and biomass of decapod crustaceans were noted there, possibly due to the cessation of spawning migrations of both marine and freshwater shrimps. The obtained results can be used as the basis for subsequent monitoring studies of the structural changes in the bottom communities of fish and decapod crustaceans of the Mekong Delta.
... As one of the world's most productive and dynamic rivers, the Mekong hosts an open-access wild capture fishery for over 1,200 fish species (Poulsen et al. 2004). The basin's 60 million people rely on the river for food and economic security, harvesting 2.2 million tons=y of fish at a retail value of up to 7.8 billion USD=y (Hortle 2009). Representing nearly 20% of global inland fish catch (Welcomme et al. 2010), the river provides up to 80% of the protein for human consumption in some areas (Hortle 2007). ...
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Home to one of the world's most biodiverse and productive freshwater fisheries, the Mekong River basin provides food and economic security to some 60 million people. The extensive hydropower development planned for the river basin has the potential to degrade this ecosystem. The basin's potentially most impactful and downstream-most proposed main stem dam, the 18-km-long Sambor Dam is to be located just upstream of critical nursery and fishery habitats of the Tonle Sap Lake and the Mekong Delta and just downstream of major spawning areas. We explore the potential to modify Sambor's siting, design, and operation (SDO) to balance hydropower and ecological outcomes. Our results demonstrate that there are opportunities to achieve more balanced ecology-energy outcomes. We use probabilistic seasonal measures of fish life cycle processes, energy production, and sediment passage to explore alternative SDO options. We consider both ecological concerns and energy production on equal footing prior to any power purchase agreements or fixed designs for Sambor, which is a first among any of the world's large dams. The Sambor Ecological Alternative (Sambor EA) dam considered in this study includes a combination of design and operational features to improve sediment and fish passage that do not exist at any of the world's large hydropower dams. Yet Sambor EA still poses a significant risk to the Mekong fishery and the millions who depend on it, given the appreciable uncertainty surrounding its potential ecological outcomes. Our results emphasize the need to address ecological concerns in advance of signing power purchase agreements that would otherwise limit the site-specific and integrated SDO modifications needed to achieve them. Our results also emphasize the importance of, and challenges in, carefully defining ecological performance measures and criteria, as well as the importance of carefully sampling reservoir operation possibilities.
The Mekong delta is host to a large number of freshwater species, including a unique group of facultative air breathing Anabantiforms. Of these, the striped snakehead (Channa striata), the climbing perch (Anabas testudineus), the giant gourami (Osphronemus goramy) and the snakeskin gourami (Trichogaster pectoralis) are major contributors to aquaculture production in Vietnam. Here we detail the gastrointestinal responses to feeding in these four species. Relative intestinal length was lowest in the snakehead, indicative of carnivory, and 5.5‐fold greater in the snakeskin, indicative of herbivory; climbing perch and giant gourami were intermediate, suggesting omnivory. N‐waste excretion (ammonia‐N + urea‐N) was greatest in the carnivorous snakehead and least in the herbivorous snakeskin, while the opposite trend was seen for net K+ excretion. Similarly, the more carnivorous species had a greater stomach acidity than the more herbivorous species. Measurements of acid–base flux to the water suggested the greatest postprandial alkaline tide occurred in the snakehead, and a potential acidic tide in the snakeskin. Additional findings of interest were high levels of both PCO2 (up to 40 mmHg) and (HCO3−) (up to 33 mM) in the intestinal chyme of all four of these air‐breathing species. Using in vitro gut sac preparations of the climbing perch, we show that intestinal net absorption of fluid, Na+, and HCO3− are upregulated by feeding, but not net Cl− uptake, glucose uptake, or K+ secretion. Upregulated net absorption of HCO3− suggests that the high chyme (HCO3−) does not result from secretion by the intestinal epithelium. The possibility of ventilatory control of PCO2 to regulate postprandial acid–base balance in these air‐breathing fish is discussed. This article is protected by copyright. All rights reserved.
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The Lower Mekong Basin (LMB), covering parts of Cambodia, Lao PDR, Thailand and Vietnam, is a biodiversity hotspot for many types of organisms, including some 1,200 fish species. The river supports one of the largest and most diverse inland fisheries in the world, with an estimated annual yield of three million tonnes. The LMB environment is still considered healthy, but the human population and the economy of the LMB countries are growing rapidly, causing an increasing rate of natural resource use. There are already signs of stress in the fishery, with increasing catches of small bodied fish and dwindling numbers of the larger species. Ongoing fisheries development activities in the LMB are described, including co-management and support to fisheries enhancement, for example stocking and aquaculture development. However, serious threats to biodiversity and fisheries arise from activities like dam construction, improvement of navigation and conversion of floodplains for agriculture. Therefore, in the LMB the primary concern for fisheries agencies may not be enhancement of the already highly productive fisheries but how to sustain acceptable yields. This will require a holistic view of the natural resources, and implies that fisheries agencies must assume a greater role in relevant policy formulation. A major impediment to integrated natural resource management is the lack of a common, cross-scale and cross-sector knowledge base. Improving the way management and policy information is generated and communicated will improve the prospects for just and rational development of fisheries and other sectors in the LMB.
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The taxonomic status of all the nominal genera of the Ariidae are reviewed and ariid genera are diagnosed by exclusive characters as well as by a combination of internal and external morphological features. The results are based on a phylogenetic analysis undertaken by the senior author (Marceniuk, 2003). The species so far recognized are taxonomically reevaluated and considered as valid, inquirendae or synonyms under each diagnosed genus based on direct examination of specimens or use of diagnostic characters available in the literature. A key to identification of genera is provided based on morphological characters that can be easily recognized. In the new classification proposed, Ariidae comprises the following twenty six valid genera: Amissidens, Arius, Aspistor, Bagre, Batrachocephalus, Brustiarius, Cathorops, Cephalocassis, Cinetodus, Cochlefelis, Cryptarius, Doiichthys, Galeichthys, Genidens, Hemiarius, Ketengus, Nedystoma, Nemapteryx, Neoarius, Netuma, Notarius, Osteogeneiosus, Pachyula, Plicofollis, Potamarius and Sciades. Three new genera are erected. The nominal genera Bagre Oken, 1817, Glanis, Stearopterus, Breviceps non Merrem, 1820, Felichthys, Ailurichthys, Mystus non Scopoli, 1777 and Anemanotus are considered junior synonyms of Bagre Cloquet, 1816. Hexanematichthys, Sciadeichthys, Selenaspis, Ariopsis and Leptarius are synonyms of Sciades. The nominal genus Pseudarius is an objective synonym, and Ariodes a subjective synonym, of Arius. Sciadeops is synonymous with Notarius. Catastoma and Sarcogenys are synonyms of Netuma. Tetranesodon is preliminary considered junior synonym of Pachyula. Hemipimelodus is a synonym of Cephalocassis. Septobranchus is a junior synonym of Cinetodus, and Guiritinga is a new synonym of Genidens.
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The Mekong is the longest river in southeast Asia. From its source on the Tibetan plateau it runs for 4,800 km through China, Myanmar, Lao PDR, Thailand, Cambodia and Viet Nam to the South China Sea, where it discharges on average 475,000 million m3 per year. The total Mekong Basin (MB) catchment area covers 795,000 km2 and has 73 million inhabitants. The Lower Mekong Basin (LMB) comprises the four countries, - Cambodia, Lao PDR, Thailand and Viet Nam - that signed the 1995 river development agreement and covers 77% of the total basin with 55 million people. The degree of inundation of the 70,000 km2 floodplains depends on the strength of the monsoon, as 85 -90 % of the discharge is generated during the wet season from May to October. Although far from pristine, the river still is in a relative good condition. Only 2 mainstream dams (in China) have been built, but many more on the tributaries. The number of fish species that has been found in the MB exceeds 2000. Many migrate across international borders, thus constituting trans-boundary resources. The largest fisheries are found in the extensive floodplains in central Cambodia and the delta. A huge variety of fishing gear is used, from the most simple traps to kilometers -long fence systems. Catch levels of the capture fisheries in the LMB are estimated to top 2.6 million tons annually with a value exceeding US$ 1.7 billion. In Cambodia fisheries contribute 16% to the GDP. Strong increases in human population are matched by equal increases in fishing effort resulting in catch levels that are probably higher than ever. Major declines in stock sizes of the larger later-in-life spawning species have been witnessed. Catches are now dominated by smaller rapidly reproducing species. Aquaculture is wide spread in the Thai and Viet Namese parts of the LMB; production is estimated at 260,000 t. In addition, 240,000 t are captured in reservoirs.
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This is the third compilation of imperiled (i.e., endangered, threatened, vulnerable) plus extinct freshwater and diadromous fishes of North America prepared by the American Fisheries Society's Endangered Species Committee. Since the last revision in 1989, imperilment of inland fishes has increased substantially. This list includes 700 extant taxa representing 133 genera and 36 families, a 92% increase over the 364 listed in 1989. The increase reflects the addition of distinct populations, previously non-imperiled fishes, and recently described or discovered taxa. Approximately 39% of described fish species of the continent are imperiled. There are 230 vulnerable, 190 threatened, and 280 endangered extant taxa, and 61 taxa presumed extinct or extirpated from nature. Of those that were imperiled in 1989, most (89%) are the same or worse in conservation status; only 6% have improved in status, and 5% were delisted for various reasons. Habitat degradation and nonindigenous species are the main threats to at-risk fishes, many of which are restricted to small ranges. Documenting the diversity and status of rare fishes is a critical step in identifying and implementing appropriate actions necessary for their protection and management.
The modern age of species concepts began in 1942, when Ernst Mayr gave concept names to several different approaches to species identification. A long list of species concepts then followed, as well as a complex literature on their merits, motivations and uses. Some of these complexities arose as a consequence of the semantic shift that Mayr introduced, in which procedures for identifying species were elevated to concepts. Much of the debate in recent decades over concepts, and over pluralism versus monism, can be seen as an unnecessary consequence of treating species identification criteria as if they were more fundamental concepts. Recently, biologists have begun to recognize both the shortcomings of a lexicon of multiple species concepts and a common evolutionary idea that underlies them.
Geographical distribution of African freshwater fishes is discussed with emphasis on the effects of major continental features, hydrographic history, and Pleistocene climatic fluctuations. Differences in the modes of dispersal and biological interactions among various categories of fishes, ecological as well as phyletic, have also had marked effects on distribution. The African continent can be divided into ten ichthyofaunal provinces. The geography of these provinces and composition of their fish faunas is briefly described. The paper concludes with a consideration of the faunistic relationships of African lakes with endemic fishes.
Botia kubotai, new species, is distinguished from all other species of the genus by its unique body colour pattern. In juveniles, three black stripes and five black bars leave four pairs of elongate yellow blotches; with increasing age, the bars and stripes widen, the yellow blotches become more slender and rows of small yellow spots are added in the stripes and in the bars. The nomenclature of Botiinae and the systematics of the South and Southeast Asian taxa are discussed. A new genus is named: Chromobotia ( type species: Cobitis macracanthus). Hymenphysa is a synonym of Botia and species usually placed in Hymenphysa should be called Syncrossus.
Wiley, E. O. (Division of Fishes, Museum of Natural History, University of Kansas, Lawrence, KS 66045). 1978. Syst. Zool. 27:17-26.-The concept of species (as taxa) adopted by an investigator will influence his perception of the processes by which species originate. The concept adopted should have as universal applicability as current knowledge permits. Simpson’s definition of a species is modified to state: A species is a lineage of ancestral descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate. This definition is defended as that which has widest applicability given current knowledge of evolutionary processes. Four corollaries are deduced and discussed relative to other species concepts: (1) all organisms, past and present, belong to some evolutionary species; (2) reproductive isolation must be effective enough to permit maintenance of identity from other contemporary lineages; (3) morphological distinctiveness is not necessary; and (4) no presumed (hypothesized) single lineage may be subdivided into a series of ancestral-descendant “species.” The application of the evolutionary species concept to allopatric demes and to asexual species is discussed and it is concluded that the lack of evolutionary divergence forms the basis for grouping such populations into single species. It is suggested that some ecological species definitions lead to under-estimations of the rate of extinction due to interspecific competition because their logical framework excludes unsuccessful species from being species. Finally, the implications of accepting an evolutionary species concept to the field of phylogeny reconstruction are discussed. [Species concepts; evolution; phylogeny reconstruction.].