Diversity and spatial distribution of freshwater fish in Great Lake and Tonle Sap river (Cambodia, Southeast Asia)

Fish catches around the Great Lake, Tonle Sap river and the transitional zo ne between the lake and the river were studied by professional 'fishing lot ' (i.e. fishing zone) from 1995 to 1997. One hundred and twenty species of fish, belonging to 26 families and nine different orders were recorded. Com pared to previous studies (1936-1976), only 53 % of families, 32 % of gener a and 54 % of species were collected by professional fishing lot. This impo rtant loss in biodiversity could have several causes: bias of sampling proc edures between professional fishing and research sampling, overfishing, mod ification of the floodplain by deforestation, etc. The professional fishing data showed that Cypriniformes accounted for 41.6 % of the total number of individuals caught, the Cyprinidae family alone represented 40 species. Si luriformes made up 21.6 %, Perciformes 13.3 %, with six other orders repres ented by smaller numbers. Eighty-seven percent of the recorded species occu r in both habitats depending on the season. Migration takes place from the Mekong river to the Gnat Lake through the Tonle Sap river at the beginning of the rainy season (May-October), and in the reverse direction at the star t of the dry season (November-February). The majority of the species reprod uce at the start of the rainy season (May-June) in the hooded plain and the forest floodplain of the Great Lake: the period, the place and the means o f reproduction have not been closely studied, particularly for the Belontif ormes, Clupeiformes, Synbranchiformes, Pleuronectiformes and Tetraodontifor mes. Multivariate analysis of fishing data (November-February) shows three distinct communities: that of the lake (Perciformes and Siluriformes), of t he river (Pleuronectiformes, Cypriniformes, Clupeiformes and Siluriformes), and of the transitional zone formed from the principal channel, the old ri ver channel and the oxbow lakes (Cypriniformes, Siluriformes and Osteogloss iformes). (C) 1999 Ifremer/Cnrs/lnra/lrd/Cemagref/Editions scientifiques et medicales Elsevier SAS.