Functional and trophic diversity of fishes in the Mekong-3S river system: comparison of morphological and isotopic patterns


The Lower Mekong River and its three major tributaries, the Sekong, Sesan, and Srepok rivers, are systems with high aquatic biodiversity that now face impacts from new hydroelectric dams. Despite the ecological, economic, and cultural importance of the freshwater biota, knowledge about aquatic ecology in this region remains poor. We used morphological and stable isotope data to explore how fish functional and trophic diversity vary between the four rivers that comprise the Mekong-3S river system. During our field surveys, the Sesan had experienced greatest flow alteration from dams and had lowest taxonomic and functional diversity, with species less packed and less evenly dispersed within morphological space compared to the other rivers. The Sekong had greatest functional diversity, with species less packed in morphological space. Species in the Mekong and Srepok were more evenly distributed in morphological space and had intermediate levels of functional diversity. Isotopic niche diversity in the Sesan did not appear to be significantly different from the Srepok and Sekong rivers. Conversely, the more species-rich Mekong fish assemblage encompassed a greater isotopic space with species less packed and evenly distributed. Greater trophic redundancy was observed amongst fishes of the 3S rivers than the Mekong. Species functional redundancy could buffer river food webs against species loss caused by dams; however, additional traits and niche dimensions should be evaluated to test this hypothesis. Overall, morphological and isotopic evidence from the Mekong and 3S rivers indicate that river impoundment and flow regulation function as an environmental filter that reduces fish functional diversity.

This is a preview of subscription content, log in to check access.

Access options

Buy single article

Instant unlimited access to the full article PDF.

US$ 39.95

Price includes VAT for USA

Subscribe to journal

Immediate online access to all issues from 2019. Subscription will auto renew annually.

US$ 199

This is the net price. Taxes to be calculated in checkout.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6


  1. Agostinho AA, Pelicice FM, Petry AC, Gomes LC, Júlio HF (2007) Fish diversity in the upper Paraná River basin: habitats, fisheries, management and conservation. Aquatic Ecosystem Health & Management 10 (2):174–186

  2. Agostinho AA, Gomez LC, Santos NC, Ortega JC, Pelicice FM (2016) Fish assemblages in Neotropical reservoirs: colonization patterns, impacts and management. Fish Res 173:26–36.

  3. Arantes CC, Fitzgerald DB, Hoeinghaus DJ, Winemiller KO (2019) Impacts of hydroelectric dams on fish and fisheries in tropical rivers through the lens of functional traits. Curr Opin Environ Sustain 37:28–40.

  4. Arrington DA, Winemiller KO (2002) Preservation effects on stable isotope analysis of fish muscle. T Am Fish Soc 131:337–342.<0337:PEOSIA>2.0.CO;2

  5. Baird IG, Meach M (2005) Sesan River fisheries monitoring in Ratanakiri province, northeast Cambodia: before and after construction of the Yali falls dam in the central highlands of Vietnam. 3S Rivers Protection Network and the Global Association for the People and the Environment, Ratanakiri

  6. Baird I, Baird M, Chum MC, Kim S, Nuon M, Phat S, Phouy BN, Prom S, Ros S, Rushton H, Sia P (2002) A community-based study of the downstream impacts of the Yali falls dam along the se san, Sre Pok and Sekong rivers in Stung Treng Province, Northeast Cambodia. Fisheries and Forestry Office, Stung Treng

  7. Baran E (2006) Fish migration triggers and cues in the lower Mekong Basin and other freshwater tropical systems. Mekong River Commission no 14, Vientiane

  8. Baran E, Saray S, Teoh SJ, Tran TC (2011) Fish and fisheries in the Sesan River basin-catchment baseline, fisheries section. The WorldFish Center, Phnom Penh

  9. Baran E, Samadee S, Jiau TS, Tran TC (2013) Fish and fisheries in the Sesan, Sekong and Srepok River basins (Mekong watershed). ICEM – International Centre for Environmental Management, Hanoi

  10. Chavent M, Kuentz-Simonet V, Labenne A, Saracco J (2014) Multivariate analysis of mixed data: the PCAmixdata R package. arXiv [stat.CO] 1411.4911

  11. Chavent M, Kuentz V, Labenne A, Liquet B, Saracco J (2017) PCAmixdata: multivariate analysis of mixed data. R package version 3.1. Accessed 29 Jan 2019

  12. Chea R, Lek S, Ngor P, Grenouillet G (2017) Large-scale patterns of fish diversity and assemblage structure in the longest tropical river in Asia. Ecol Freshw Fish 26:575–585.

  13. Conlan I, Rutherfurd I, Finlayson B, Western A (2008) The geomorphology of deep pools on the lower-Mekong River: controls on pool spacing and dimensions, processes of pool maintenance and potential future changes to pool morphology. Final report submitted to the Mekong River Commission Secretariat. Vientiane, Lao

  14. Core Team R (2018) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna

  15. Dugan PJ, Barlow C, Agostinho AA, Baran E, Cada GF, Daqing C, Cowx IG, Ferguson JW, Jutagate T, Mallen-Cooper M, Marmulla G, Nestler JM, Petrere M, Welcomme RL, Winemiller KO (2010) Fish migration, dams, and loss of ecosystem services in the Mekong Basin. Ambio 39:344–348.

  16. Fitzgerald DB, Winemiller KO, Sabaj-Pérez MH, Sousa LM (2017) Using trophic structure to reveal patterns of trait-based community assembly across niche dimensions. Funct Ecol 31:1135–1144.

  17. Gatz AJ Jr (1979a) Ecological morphology of freshwater stream fishes. Tulane Studies Zool Bot 21:91–124

  18. Gatz AJ Jr (1979b) Community organization in fishes as indicated by morphological features. Ecology 60:711–718

  19. Hap N, Un S, Nasielski J (2016) A review of socioeconomic studies in the fisheries sector in Cambodia. Inland Fisheries Research and Development Institute (Fisheries Administration) and WorldFish, Phnom Penh

  20. Hirsch P, Wyatt A (2004) Negotiating local livelihoods: scales of conflict in the Se San River basin. Asia Pac Viewp 45:51–68.

  21. Hoeinghaus DJ, Zeug S (2008) Can stable isotope ratios provide for community-wide measures of tropic structure? Comment. Ecology 89:2353–2357

  22. Jackson AL, Inger R, Parnell AC, Bearhop S (2011) Comparing isotopic niche widths among and within communities: SIBER – stable isotope Bayesian ellipses in R. J Anim Ecol 80:595–602.

  23. Johnson PTJ, Olden JD, Zanden MJV (2008) Dam invaders: impoundments facilitate biological invasions into freshwaters. Front Ecol Environ 6:357–363.

  24. Kondolf GM (1997) Hungry water: effects of dams and gravel mining on river channels. Environ Manag 21:533–552.

  25. Layman CA, Arrington DA, Montaña CG, Post DM (2007) Can stable isotope ratios provide for community-wide measures of trophic structure? Ecology 86:2530–2535.[42:CSIRPF]2.0.CO;2

  26. Lévêque C, Oberdorff T, Paugy D, Stiassny MLJ, Tedesco PA (2008) Global diversity of fish (Pisces) in freshwater. Hydrobiologia 595:545–567.

  27. Li J, Dong S, Peng M, Yang Z, Liu S, Li X, Zhao C (2013) Effects of damming on the biological integrity of fish assemblages in the middle Lancang-Mekong River basin. Ecol Indic 34:94–102.

  28. Liem KF (1990) Aquatic versus terrestrial feeding modes: possible impacts on the trophic ecology of vertebrates. Am Zool 30:209–221.

  29. Liermann CR, Nilsson C, Robertson J, Ng RY (2012) Implications of dam obstruction for global freshwater fish diversity. Bioscience 62:539–548.

  30. Lima AC, Sayanda D, Agostinho CS, Machado AL, Soares AMVM, Monaghan KA (2018) Using a trait-based approach to measure the impact of dam closure in fish communities of a Neotropical River. Ecol Freshw Fish 27:408–420.

  31. Mekong River Commission (2005) Work program report. Mekong River Commission, Vientiane

  32. Mekong River Commission (2010) State of the basin report 2010. Mekong River Commission, Vientiane

  33. Mekong River Commission (2015) Strategic plan 2010–2015. Mekong River Commission, Vientiane

  34. Mims MC, Olden JD (2013) Fish assemblages respond to altered flow regimes via ecological filtering of life history strategies. Freshw Biol 58:50–62.

  35. Montaña CG, Winemiller KO (2013) Evolutionary convergence in Neotropical cichlids and Nearctic centrarchids: evidence from morphology, diet and stable isotope analysis. Biol J Linn Soc 109:146–164.

  36. Montaña CG, Winemiller KO, Sutton A (2014) Intercontinental comparison of fish ecomorphology: null model tests of community assembly at the patch scale in rivers. Ecol Monogr 84:91–107.

  37. Ngor PB, Legendre P, Oberdorff T, Lek S (2018) Flow alterations by dams shaped fish assemblage dynamics in the complex Mekong-3S river system. Ecol Indic 88:103–114.

  38. Nilsson C (2005) Fragmentation and Flow Regulation of the World's Large River Systems. Science 308 (5720):405–408

  39. Oksanen J, Blanchet FG, Friendly M, Kindt R, Legendre P, McGlinn D, Minchin PR, O'Hara RB, Simpson GL, Solymos P, Stevens MHH, Szoecs E, Wagner H (2017) vegan: Community Ecology Package. R package version 2.4–3. Accessed 29 Jan 2019

  40. Oliveira AG, Baumgartner MT, Gomes LC, Dias RM, Agostinho AA (2018) Long-term effects of flow regulation by dams simplify fish functional diversity. Freshw Biol 63:293–305.

  41. Ou C, Winemiller KO (2016) Seasonal hydrology drives shifts in production sources supporting fishes in the lower Mekong River basin. Can J Fish Aquat Sci 73:1342–1362.

  42. Ou C, Montaña CG, Winemiller KO (2017) Body size and trophic position relationships among fishes of the lower Mekong Basin. R Soc Open Sci 4:160645.

  43. Pelicice FM, Azevedo-Santos VM, Vitule JRS, Orsi ML, Lima DP, ALB M Jr, Pompeu PS, Petrere M Jr, Agostinho AA (2017) Neotropical freshwater fishes imperiled by unsustainable policies. Fish Fish 10:1–15.

  44. Petrere M Jr (1996) Fisheries in large tropical reservoirs in South America. Lakes Reserv Res Manag 2(1–2):111–133.

  45. Piman T, Cochrane TA, Arias MA, Green A, Dat ND (2013) Assessment of flow changes from hydropower ddevelopment and operations in Sekong, Sesan, and Srepok River of the Mekong Basin. J Water Res Plan Man 139:723–732.

  46. Poff NL, Olden JD, Merritt DM, Pepin DM (2007) Homogenization of regional river dynamics by dams and global biodiversity implications. Proc Natl Acad Sci USA 104:5732–5737.

  47. Pokhrel Y, Shin S, Lin Z, Yamazaki D, Qi J (2018) Potential disruption dynamics in the lower Mekong River basin due to upstream flow regulation. Sci Rep 8:17767.

  48. Post DM (2002) Using stable isotope to estimate trophic position: models, methods, and assumptions. Ecology 83:703–718.[0703:USITET]2.0.CO;2

  49. Robinson BW, Wilson DS (1998) Optimal foraging, specialization, and a solution to Liem’s paradox. Am Nat 151:223–235

  50. Santos NL, Santana HS, Ortega JC, Diaz RM, Stegmann LF, Araujo IMS, Severi W, Bini LM, Gomes LC, Agostinho AA (2017) Environmental filters predict the trait composition of fish communities in reservoir cascades. Hydrobiologia 802:245–253.

  51. Sithirith M (2016) Dams and state security: damming the 3S rivers as a threat to Cambodian state security. Asia Pac Viewp 57:60–75.

  52. Toussaint A, Charpin N, Brosse S, Villéger S (2016) Global functional diversity of freshwater fish is concentrated in the Neotropics while functional vulnerability is widespread. Sci Rep 6:22125.

  53. Try T, Chambers M (2006) Situation analysis: Stung Treng Province, Cambodia. Mekong Wetlands Biodiversity Conservation and Sustainable Use Programme, Vientiane

  54. Wainwright PC, Alfaro ME, Bolnick DI, Hulsey CD (2005) Many-to-one mapping of form to function: a general principle in organismal design? Integr Comp Biol 45:256–262.

  55. Webb PW (1984) Body form, locomotion and foraging in aquatic vertebrates. Integr Comp Biol 24:107–120.

  56. Whyatt A, Baird IG (2007) Transboundary impact assessment in the Sesan river basin: the case of the Yali falls dam. Water Res Devel Man 23:427–442.

  57. Winemiller KO (1991) Ecomorphological diversification of freshwater fish assemblages from five biotic regions. Ecol Monogr 61:343–365.

  58. Winemiller KO, McIntyre PB, Castello L, Fluet-Chouinard E, Giarrizzo T, Nam S, Baird IG, Darwall W, Lujan NK, Harrison I, Stiassny ML, Silvano RA, Fitzgerald DB, Pelicice FM, Agostinho AA, Gomes LC, Albert JS, Baran E, Petrere M Jr, Zarfl C, Mulligan M, Sullivan JP, Arantes CC, Sousa LM, Koning AA, Hoeinghaus DJ, Sabaj M, Lundberg JG, Armbruster J, Thieme ML, Petry P, Zuanon J, Torrente Vilara G, Snoeks J, Ou C, Rainboth W, Pavanelli CS, Akama A, van Soesbergen A, Sáenz L (2016) Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong: basin-scale planning is needed to minimize impacts in mega-diverse rivers. Science 351:128–129.

  59. Ziv G, Baran E, Nam S, Rodríguez-Iturbe I, Levin SA (2012) Trading-off fish biodiversity, food security, and hydropower in the Mekong River basin. Proc Natl Acad Sci USA 109:5609–5614.

Download references


We thank the citizens of Stung Treng, Siem Pang, Veurn Sai, and Lomphat in Cambodia for their help with fieldwork. We also thank So Nam and the Inland Fisheries Research and Development Institute of Cambodia for logistic support and providing a scientific permit, and Putrea Solyda for help with fieldwork, logistics, and relations with the local communities. Funding for this project was provided by the Estate of Carolyn and George Kelso via the International Sport Fish Fund at Texas A&M.

Author information

Correspondence to Carmen G. Montaña.

Ethics declarations

Ethical approval

Fish specimen collection and export permits for this study were granted to Chouly Ou by the Inland Fisheries Research and Development Institute (IFReDI) of Cambodia. IFReDI personnel supervised and assisted sampling. During our field study, IFReDI had not yet established animal use protocols; therefore, guidelines established by the American Fisheries Society (UFR Committee, 2004. Guidelines for the use of fishes in research. American Fisheries Society, Bethesda, MD) were adopted.

Additional information

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Electronic supplementary material


(DOCX 26 kb)


(DOCX 16 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Montaña, C.G., Ou, C., Keppeler, F.W. et al. Functional and trophic diversity of fishes in the Mekong-3S river system: comparison of morphological and isotopic patterns. Environ Biol Fish 103, 185–200 (2020).

Download citation


  • Cambodia
  • Fish assemblage
  • Functional trait
  • Isotopic niche
  • Stable isotope analysis