Abstract—Water quality and freshwater fish diversity from nine waterfalls at Khao Luang National Park, Thailand was examined. Streams were shallow, fast flowing with clear water and rocky and sandy substrate. The mean water quality of waterfalls at Khao Luang National Park were as following pH 7.50, air temperature 24.27 °C, water temperature 26.37 °C, dissolved oxygen 7.88 mg/l, hardness 4.44-21.33 mg/l, alkalinity 3.55-11.88 mg/(as CaCO 3 ). Twenty fish species were found at Khao Luang National Park belonging to nine families. A cluster analysis of water quality at Khao Luang National Park revealed that waterfalls at Khao Luang National Park were divided into two groups: A and B. Group A composed of two waterfalls (i.e. Aie Kaew and Wangmaipak) that flew to the Gulf of Thailand side. Group B composed of seven waterfalls (i.e. Promlok, Kalom, Nuafa, Suankun, Soidaw, Suanhai, and Thapae) that flew to the Andaman Sea side (Fig. 2) .The Cyprinids represented the major species in all the waterfalls comprising of 45%. Keywords—Water quality, Freshwater fishes, National Park, Khao Luang, Thailand. I. INTRODUCTION HAILAND is located in the tropics with many different ecosystems and a great diversity of fish species. [1]. A previous fish survey in Nakhon Si Thammarat Province (Tapee watershed, Trang watershed, and other watersheds) was undertaken using native and electro-fishing techniques. A total of 112 freshwater fish species was recorded. The dominant family was Cyprinidae. Based on the survey report on fundamental natural resources in 2005, fishes found at Khao Luang National Park showed the vast diversity of freshwater fish only in the running water sites and there were found only seven fish species from 3 orders, 5 genera, 7 Manuscript received November 30, 2006. This work was supported in part by PPT Public Company Limited, TRF/Biotec special program for Biodiversity Research Training grant BRT T_148017 and CXKURUE, the Institute of Research and Development, Walailak University. Sutin S. is with School of Science, Walailak University, 222 Thaiburi, Thasala District, Nakhonsithammarat 80161, Thailand and Faculty of Science, Rajabhat Nakhon Si Thammarat University, Muang, Nakhon Si Thammarat 80280 (phone: +66 75 318 355; Fax: +66 75 318 356; e-mail: asuparporn@yahoo.com). Jaroensutasinee M. is with School of Science, Walailak University, 222 Thaiburi, Thasala District, Nakhonsithammarat 80161, Thailand (phone: +66 75 672 005; Fax: +66 75 672 004; e-mail: jmullica@wu.ac.th). Jaroensutasinee K. is with School of Science, Walailak University, 222 Thaiburi, Thasala District, Nakhonsithammarat 80161, Thailand (phone: +66 75 672 005; Fax: +66 75 672 004; e-mail: krisanadej@gmail.com). families. Among these seven species, two species were reported to be found only in the Southern Thailand. These two species were Clarias sp. found in Kiriwong streams and Trichopsis vittatus found in the streams of lowland. The study on the habitat of Clarias sp. in Ban Plai Uan, Promlok district, Nakhon Si Thammarat province revealed that freshwater fishes living in the running water ecosystem always hide in the roots of the trees, holes under leaves and under stones. Clarias sp. is a noctural fish. Fishes that are always found in the habitat of Clarias sp. are pigmy gourami (Trichopsis vittatus), Channa limbata, blue danio (Brachydanio albolineata), brook carp (Neolissocheilus soroides), T-barb, spanner barb (Puntius lateristriga), and stone- lapping fish (Garra taeniata) [2]. Khao Luang National Park is dominated by a rugged mountain range running north to south. The area contains a large tropical rainforest, wildlife habitats, and many waterfalls. Protected areas such as national parks could play an important role in the conservation of freshwater fish in Thailand, but there is a need to better identify and assess the conservation value of these areas in relation to bio- geographical diversity of fish population and the habitat characteristics of fish communities. However, only few studies of freshwater fish fauna in the Khao Luang National Park have been carried out to date. This study aimed at examining water quality and freshwater fish diversity in the streams of the waterfalls at Khao Luang National Park. The findings from the study will also benefit the planning and management of sustainable fisheries and conservation of natural resources at national level. II. MATERIALS AND METHODS A. Study Area Khao Luang National Park was declared as the 9 th National Park of Thailand on 18 th December 1974. The landscape is rugged mountain range which lays down from north to south, about 40 km long. The study was undertaken at nine waterfalls: Aie-kaew, Wangmaipak, Promlok, Kralom, Tapae, Suankun, Nuafa, Suanhai and Soidaw Waterfalls (Fig. 1), from July-September 2004. S. Sutin, M. Jaroensutasinee, and K. Jaroensutasinee Water Quality and Freshwater Fish Diversity at Khao Luang National Park, Thailand T World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:1, No:12, 2007 112 International Scholarly and Scientific Research & Innovation 1(12) 2007 scholar.waset.org/1307-6892/10370 International Science Index, Environmental and Ecological Engineering Vol:1, No:12, 2007 waset.org/Publication/10370