AquaFish CRSP Project USAID Grant No.: EPP-A-00-06-00012-00 "Development of Alternatives to the Use of Freshwater Low Value Fish for Aquaculture in the Lower Mekong Basin of Cambodia and Vietnam: Implications for Livelihoods, Production and Markets"

We defined inland small-sized fish species in lower Mekong River basin of Cambodia and Vietnam as species that generally has a maximal total length of equal to or less than 25 cm and a low market value, generally 5 to 10 times lower a market value of big-sized or commercially important fish species. The lower Mekong River basin of Cambodia and Vietnam was very rich in small-sized fish species diversity. In total, at least 200 inland smallsized fish species are found and identified. Many of these small-sized fish species were truly abundant in the region. The most abundant small-sized fish was Trey riel in Khmer or Ca linh ria in Vietnamese (mainly Cirrhinus siamensis and C. lobatus). Top ten small-sized fish species were also identified in both countries Cambodia and Vietnam. The proportion of small-sized fish species was more than 80% of the total inland fish catch. Of the total inland small-sized fish catch, juvenile of big-sized fish varied from 35 to 51%. Aquaculture of carnivorous (including snakeheads) and omnivorous fish species in the lower Mekong River basin of Cambodia and Vietnam was highly dependent on inland fisheries of small-sized fish for sourcing key dietary nutrient inputs. The ban on snakehead farming in Cambodia seemed to be not effective as resources for implementation are lacking. The use of inland small-sized fish for snakehead farming in the Mekong Delta of Vietnam had both negative and positive impacts. This study had very important implications for sustainable utilization and management of inland small-sized fish resource and for sustainable development of snakehead aquaculture in the lower Mekong River basin of Cambodia and Vietnam. Introduction The Mekong (Fig. 1) is the twelfth longest river in the world, the seventh longest river in Asia, and the longest river in Southeast Asia (Rainboth, 1996). It is born in the glaciers over 5,000 m above sea level in the Tibetan Himalayas, from where it flows through six countries (China, Myanmar, Laos, Thailand, Cambodia and Vietnam) for 4,880 km before it empties into the South China Sea in southern Vietnam. It has a drainage area of 802,900 km and an average runoff of 475,000 million m (Rainboth, 1996). As the Mekong passes into Cambodia it flows over the Khone Falls (the highest natural water fall, with an elevation drop of 21 m) and follows a nearly straight course with many stretches of rapids through eastern Cambodia. In eastern Cambodia (Kratie province), river flow records indicate that the seasonal discharge of the Mekong has a rainy season maximum to dry season minimum ratio of 53.6. This seasonal flow change is much more pronounced in the Mekong than in any other great river of the world (Welcomme, 1979). Between June and September/October, when the Mekong floods are rising in Chaktomouk (also known as Quatre Bras), the discharge is diverted into three branches: (1) the Mekong proper, also named Lower Mekong or Mekong Krom in Cambodian (which receives 62 to 68% of the flow; (2) Bassac River (receiving 12 to 14%); and (3) Tonle Sap (also named Great Lake) (receiving 11 to 23%).