DIVERSITY OF FISH IN HAU RIVER, MEKONG DELTA, VIETNAM

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1 DIVERSITY OF FISH IN HAU RIVER, MEKONG DELTA, VIETNAM Vu Ngoc Ut 1, Au Van Hoa 1, Nguyen Bach Loan 1 ABSTRACT The study on diversity of fish in the Hau River was continuously implemented during 12 months (July, 2011 to June, 2012) at An Giang (upstream), Can Tho (middle stream) and Soc Trang (downstream). At each area, sampling was conducted at 2 sites (main river and its tributary) using the main fishing gear as trawl net in combination with other available fishing years such as gill nets, fixed nets, lift nets and at the local fish markets. The results showed that a total of 192 fish species belonging to 16 orders and 49 families was recorded. The most abundant order containing 58 species accounting for 30.2% was Perciformes and the least was Characiformes containing only 1 species. The number of fish species was declining from the upper to lower parts. At the upstream (An Giang), 145 species were recorded followed by Can Tho with 121 species and only 107 species in Soc Trang. The fish species composition was also significantly different from upstream to downstream and between sampling periods. Overall, highest number of species ( ) was recorded in January, February and April; and lowest number (40) was recorded in July; the remaining months contained 71 to 98 species. At down stream area, highest species number was recorded in March with 48 species and followed by January with 45 species; and lowest number recorded in May with only 24 species among 107 species. Keywords: fish biodiversity; Hau River; species compositions I. INTRODUCTION The Mekong Delta (MD) is well known with a dense system of rivers and canals which is the most favorable condition for growth and evolution of aquatic fauna and flora. This also results in diversity of these communities. Hau River or Bassac River is the biggest branch of Mekong River in the lower basin. With a length of 226 km, Hau River flows through different areas of the MD including An Giang (104 km), Can Tho (48km), Hau Giang (15km) and Soc Trang (59km) carrying substantial aquatic resources which contribute significantly to the freshwater fishery production of the region, in which fish is the main and vital component. There quite numbers of researches and projects have been conducted to investigate the composition and diversity of fish in the last decades, however with different sampling methodologies, timing and sites resulting in slightly different number of species. Mai Dinh Yen et al. (1992) found 255 species of fish belonging to 45 families and 14 orders; while Truong Thu Khoa and Tran Thi Thu Huong (1993) reported only 175 species belonging to 39 families and 13 orders. A recent investigation covering much larger areas including mud flat and mangrove ecosystems and by all used fishing gears has revealed that a total of 322 fish species belonging to 77 families recorded (Tran Dac Dinh et al., 2013). However, a detailed study on monthly fluctuation of fish species composition on a specific habitat such as Hau River has not been implemented as yet. Poulsen et al. (2005) reported that there are 40 important fish species in the Mekong 1 College of Aquaculture and Fisheries, Can Tho University, vnut@ctu.edu.vn NHA TRANG UNIVERSITY 167

2 lower basin in which 9 species are endemic and 3 endangered species that could become extinction. The important endemic species need to be protected include Tenualasa thibaudeaui, Cirrhinus lobatus, Hampala dispar, Pangasianodon gigas, Puntioplitas falcifer, Probarbus jullieni and Aaptosyax gypus. These authors also warned that 3 species could be disappeared including Laotian shad (Tenualasa thibaudeaui), Isok barb (Probarbus jullieni) and Giant catfish (Pangasianodon gigas). Previous study also revealed the declining in fisheries resource in Hau River (Berra, 2001; Pitcher & Hollingworth, 2002; Nguyen Thanh Tung et al., 2007). The findings from a study in the upstream area (An Giang province) of Hau River by Nguyen Thanh Tung et al. (2007) revealed that 7 species were in the endangered status which could not be regularly encountered including Pangasianodon gigas, Pangasius sanitwongsei, Dasyatis laosensis, Pristis microdon, Chitala blanci, Tenualosa thibaudeaui, and Orcaella brevirostris. According to these authors, the causes of the decline could be overexploitation, habitat loss, pollution and dam construction. Particularly, under high pressure of increased human population which leads to high demand of fish food consumption, the fisheries resource is more impacted. Investigation on specific fish composition and resource fluctuation is very indispensable to provide important baseline for proper monitoring and managing the resources in the Bassac River, lower Mekong river basin. II. MATERIALS AND METHODS The study was implemented for 12 months from June 2011 to July 2012 on Hau/Bassac River. Sampling was conducted monthly at 3 main areas including An Giang (upstream), Can Tho (middle stream) and Soc Trang (lower stream) in the full moon period. At each area, samples were collected at 2 sites/stations (Figure 1 and Table 1). Table 1. Sampling sites on Hau river Figure 1. Sampling sites selected on Hau River An Giang (Upstream) Can Tho (Middle stream) Soc Trang (Downstream /Estuary) Khanh An 10 o o Vam Nao 10 o o Thot Not Freshwater Freshwater 10 o o Freshwater Ninh Kieu 10 o o Dai Ngai 09 o o Tran De 09 o o Freshwater Seasonal brackish water Seasonal brackish water Fish samples were collected by trawl nets which were operated regularly on the monthly basis. The nets had a frame size of 0.5 m high and 3.5 m wide dragging over the bottom of the river for approximately 20 minutes. In addition to direct sampling, fish were also collected from other fishing gears including gill nets, fixed nets and lift nets which were being operated at the same time in the surrounding areas. The sample collection was regularly conducted at the same day of direct sampling for each site. The same fishing gears were 168 NHA TRANG UNIVERSITY

3 chosen for indirect sampling at all sites. Fish specimens were cleaned and transferred to the laboratory of College of Aquaculture and Fisheries, Can Tho University for analysis. Fish were identified by measuring and counting different morphological parameters including total length, standard length, dorsal fin, pelvic fin, pectoral fin, lateral scale number, based on the taxonomic keys published by Vuong Di Khang ( ), Nguyen Khac Huong (1991), Truong Thu Khoa and Tran Thi Thu Huong (1993), Rainboth (1996) and Fishbase (2012). Data were treated and compared between areas to illustrate the differences in species number and composition among the study areas. III. RESULTS AND DISCUSSIONS A total of 192 fish species was recorded during 12 months of sampling at 6 sites. These species belong to 49 families and 16 orders in which the Perciformes was the most abundant order with 58 species accounting for 30% followed by the Cypriniformes with 52 species contain only one representative species were Scopeliformes, Anguilliformes, Characiformes Among the recorded species, 25 of them are highly economical valuable. Two invasive species were found including sucking fish or vermiculated sailfin catfish (Pterygoplichthys disjunctivus) and pirapitinga (Piaractus brachypomus). The sucking fish was found in most of the natural water bodies and the pirapitinga found in all inland river systems at Can Tho and An Giang, especially in the tributaries even at the estuary. In addition, importantly, six endangered species were recorded including laotian shad Tenualosa thibaudeaui, white sardine Kowala coval (Clupeiformes), glass barb Parachela oxygastroides, red tinfoil barb, Barbonymus schwanenfeldii, siamese giant barb Catlocarpio siamensis (Cypriniformes) and saddle grunt Pomadasys maculates (Perciformes). Fish species number and composition in this study was partly similar and different from (27.1%). The least abundant orders which previous studies (Table 2). Table 2. Similarity and difference in species number and composition between this study and previous studies Authors Similarity to previous studies Difference to previous studies No of species Percent (%) No of species Percent (%) Vuong Di Khang ( ) Mai Dinh Yen et al. (1992) Truong Thu Khoa and Tran Thi Thu Huong (1993) Rainboth (1996) The similarity of species composition between this study and the previous studies is quite low. This could be related to the difference in geographic and ecological features between study sites. For example, the study by Vuong Di Khang ( ) was conducted mostly in the coastal areas where more brackish water fish were recorded while most of fish species in this study was from the freshwater parts. In contrast, 34.4% of species in this study is different from the study conducted by Truong Thu Khoa and Tran Thi Thu Huong (1993) who sampled mostly in the freshwater areas of the Mekong Delta, NHA TRANG UNIVERSITY 169

4 whereas more brackish water species recorded in this study (more than 20 species) as sampling was conducted further down to the estuary on Hau River. Number of species was different and decreasing from upstream to downstream. At the upstream (An Giang), 145 species belonging to 13 orders were found in which the Cypriniformes was the most dominant group with highest species number (47 species, accounting for 32.41%), followed by Perciformes with 35 species (24.14%). The other orders comprised only 1-9 species (Figure 2). Figure 2. Fish species composition recorded at the upstream (An Giang) of Hau River The commonly encountered species in this area were hampala barb Hampala macrolepidota, beardless barb Cyclocheilichthys apogon, Pangasius conchophilus and Belodontichthys dinema. However, some species were encountered only once such as Laotian shad Tenualosa thibaudeaui and glass barb Parachela oxygastroides. Species listed in the Vietnam Red Data Book (Dang Ngoc Thanh et al., 2007) were also found in this area including Isok barb Probarbus jullieni, small scale mud carp Cirrhinus microlepis, giant barb Catlocarpio siamensis, and spotted archerfish Toxotes charareus. However, the occurrence frequency of these species was very low. Probarbus jullieni was found only once in March. Toxotes charareus occurred more but 3 times only in January, February and June. Cirrhinus microlepis was recorded 4 times in March, April, September and October. Catlocarpio siamensis, particularly was not found in this area during the sampling period. This would confirm the scarce level of this species which is listed in the Red list of IUCN as CR (critical endangered) species (Hogan, 2013). The fish species composition in the upstream area was also investigated by previous studies. Nguyen Thanh Tung et al. (2007) recorded 130 species of 40 families and 13 orders, in which Cypriniformes was also the most dominant group with 46 species, following by Siluriformes with 33 species and Perciformes with 27 species. This study also revealed at least 7 species which ever occurred but no longer found in this area such as Pangasius sanitwongsei, Chitala blanci, Dasyatis laosensis, Pritis microdon, Orcaella brevirostris, giant catfish Pangasianodon gigas and laotian shad Tenualosa thibaudeaui. Total number of species found by Nguyen Thanh Tung et al. (2007) was 15 species less than that of this study. In addition, Tenualosa thibaudeaui, the valuable and rare species was only recorded in this study but not from other previous studies although it was recorded only in June. 170 NHA TRANG UNIVERSITY

5 At the middle stream (Can Tho), the species number was lower with 121 species of 12 orders. The Cypriniformes (37 species) was also the most abundant order followed by Perciformes (35 species). The Siluriformes was also diverse with high number (27 species) while other orders such as Gasterosteiformes, Characiformes, Synbranchiformes and Tetraodontiformes had only 1 species (Figure 3). Figure 3. Fish composition recorded at the midstream (Can Tho) of Hau River The most commonly encountered species in this area were Cirrhinus jullieni, Labiobarbus order found in this area was Perciformes with 43 species (40.2%), followed by Siluriformes, siamensis, black shark minnow Labeo 18 species (16.8%) and Cypriniformes, 17 chrysophekadion, moonlight gourami species (15.9%). The other orders contributed Trichogaster microlepsis, snakehead 1-9 species accounting for % (Figure Channa striatus, duskyfin glass fish 5). Some typical estuarine fish species Parambassis wolffii, pale rasbora Rasbora encountered included Siganus fuscescens, aurotaenia. Isok barb Probarbus jullieni, giant Pomadasys maculates, Sillago sihama barb Catlocarpio siamensis and (Perciformes), Harpadon nehereus Scaphognathops bandanensis were recorded (Scopeliformes) and 3 species of only once during the study period. Batrachoidiformes, Aploactis sp., Batrachomoeus At the downstream (estuary), the number trispinosus, and Halophryne diemensis. of species was much lower compared to the mid and upstream areas. There were only 107 However, some freshwater fish also occurred in this area such as Cirrhinus jullieni, species of 12 orders recorded in this area. Micronema bleekeri, and silver barb Unlike the other areas, the most dominant Barbonymus gonionotus. Figure 4. Fish composition recorded at the downstream (Soc Trang) of Hau River NHA TRANG UNIVERSITY 171

6 The species number varied slightly during the sampling period at the estuary. Highest number of species was obtained in March with 48 among 107 species recorded at this area. Followed by January with 45 species and species in the following months. Lowest number of species was recorded in May with only 24 species. Species that occurred in most of the time in a year were Arius sciurus, Polynemus longipectoralis, Plotosus canius, Glossogobius giurus, Parapocryptes serperaster, Johnius weberi, Coilia macrognathos. Apparently, the diversity or fish number decreases from upstream to downstream (Figure 5). This variation could be due to the differences of habitats related to salinity and salinity tolerance of fish. Salinity is variable with tide and season at the estuary leading to variation in distribution of fish. Typical brackish water fish cannot be found at upstream or even midstream such as species of order Scopeliformes, Scorpaeniformes and Batrachoidiformes. Similarly, fish belonging to typical freshwater orders were not recorded at the estuary such as Osteoglossiformes, Gasterosteiformes, Synbranchiformes and Tetraodontiformes. Figure 5. Number of fish species in different area of Hau River There was only 30% (58 species) of Can Tho and Soc Trang possessed 62 (32.3%) total species occurring concurrently in all 3 common species whereas 71 (37.0%) common sampling areas including An Giang (upstream), species was recorded at An Giang and Soc Can Tho (midstream) and Soc Trang Trang. Typical species that found only at each (downstream). Between An Giang and Can Tho, there were 108 species accounting for area was 27, 10 and 33 for An Giang, Can Tho 56.3% occurred concurrently in these areas. and Soc Trang, respectively (Figure 6). Figure 6. The concurrently existing species in different areas of Hau River 172 NHA TRANG UNIVERSITY

7 It is obvious that number of fish species found in this study was lower than that recorded by Mai Dinh yen et al. (1992) who found 255 species of 131 genus, 45 families and 14 orders in the sea of South of Vietnam. However, the number was higher than that from the investigation conducted by Truong Thu Khoa and Tran Thi Thu Huong (1993) with only 175 species. Recently, findings from Tran Dac Dinh et al (2013) also revealed the higher number of species in the Mekong Delta with 322 species. However, due to different sampling methods, timing, areas by different studies leading to uncommon data on fish species number. Mai Dinh Yen et al (1992) conducted their sampling not only in the Mekong Delta including Hau River and Tien River but also in Dong Nai, Sai Gon, Vam Co rivers as well as Dong Thap Muoi, U Minh wetlands and Phu Quoc island. Their study covered a large area of the South of Vietnam which had resulted in a high recorded number of fish species. Truong Thu Khoa and Tran Thi Thu Huong (1993) implemented their study also in Hau and Tien River, however, the number of fish species was lower as compared to the result of this study. High number of fish species found by Tran Dac Dinh et al (2013) was the results of comprehensive investigation on all different habitats in the Mekong Delta including mudflat and mangrove ecosystem. Furthermore, they also used most of common fishing gears utilized to catch fish in the Mekong Delta. In this study, fish species composition was only studied in Hau River and its first tributaries and sampled by a few types of fishing gears that were available in the study areas. Many groups of fish therefore may not be accessed. IV. CONCLUSIONS Total fish species recorded in Hau River was 192 species belonging to 49 families and 16 orders. The number of fish species decreases from up to downstream with 145, 121 and 107 species in upstream, midstream and downstream, respectively. Species composition was slighly different from upstream to downstream due to changes in ecological features. Two exotic species were recorded including Pterygoplichthys disjunctivus and Piaractus brachypomus. Few species were scarcely encountered and also listed in the Red list of IUCN which should be protected with proper management. REFERENCES 1. Berra, T., Freshwater fish distribution. Academic Press, Sandiego, California, USA, 604 pp. 2. Dang Ngoc Thanh and Ho Thanh Hai, Vietnam Animals (Dong Vat chi Viet Nam). Science and Technology Publisher, 239pp. 3. Dang Ngoc Thanh (Ed), Vietnam Red Data book. Part I Animals. Natural Science and Technology Publisher, 515pp. 4. Hogan, Z., Catlocarpio siamensis. The IUCN Red List of Threatened Species. Version <www. iucnredlist.org>. Downloaded on 01 May Mai Dinh Yen, Nguyen Van Trong, Nguyen Van Thien, Le Hoang Yen and Hua Bach Loan, Identification of freshwater fish in the South of Vietnam. Science and Technology Publishing House, 350pp. 6. Nguyen Khac Huong, Vietnam marine fish. Part 2, Volume 1. Science and Technology Publishing house, 182pp (in Vietnamese). NHA TRANG UNIVERSITY 173

8 7. Nguyen Thanh Tung, Phan Thanh Lam, Nguyen Khac Thanh, Truong Thanh Tuan, Nguyen Nguyen Du, Lam Ngoc Chau, Vu Vi An, Nguyen Van Thanh and Tran Anh Dung, Report on investigation of presence of freshwater species in An Giang. Department of Science and Technology, An Giang province, 196pp. (in Vietnamese). 8. Pitcher, T.J. & Hollingworth,C.E., Recreational Fisheries: Ecological, Economical and Social Evaluation. Fish and Aquatic Resources Series No 8, Blackwell Science, Oxford, UK, 288pp. 9. Rainboth, W. J., Fishes of the Cambodian Mekong. FAO species Identification Field Guide for Fishery Purposes. FAO, Rome, 265p. 10. Tran Dac Dinh, Shibukawa Koichi, Nguyen Thanh Phuong, Ha Phuoc Hung, Tran Xuan Loi, Mai Van Hieu and Utsugi Kenzo, Fishes of the Mekong Delta, Vietnam. Can Tho University Publishing House, 174pp. 11. Truong Thu Khoa and Tran Thi Thu Huong, Identification of freshwater fish in the Mekong Delta. Faculty of Fisheries, Can Tho University, 361pp. (In Vietnamese). 12. Vuong Di Khang, Ichthyology taxonomy. Publisher of Shanghai Science, Technology and Hygiene, 843pp. (Translated by Nguyen Ba Hao) dated NHA TRANG UNIVERSITY