The Middle Reaches Of The Mekong River Fish Fauna And (catfish) Is A Migratory Path

Lancang-Mekong River gave birth to the world’s richest ecosystems of freshwater fish. There are thousand known kinds of fishes in the entire basin. Fish diversity in the Mekong River is the third highest in the world’s major rivers, it only less than the diversity of the Amazon River and the Zaire River basin. The fishers are not only as an important economic industry, but also the food source in the riparian countries especially those downstream countries. This paper aims to clarify the fish fauna and the distribution pattern of the middle reaches of the Mekong River, analysis the relationship of geographic distribution and environmental factors, and discusses the migratory characteristics of the important genus.The freshwater fish data in this study from the MFD (Mekong fish database), and the Environmental Data were derived from Worldclim. The middle reaches of the Mekong River is divided into41regions with the help of GIS data preprocessing. Correlation, stepwise regression, clustering and principal component analysis methods were used to explore distribution patterns of freshwater fishes. The results are as follows.1) We found363freshwater fish species in the middle reaches of the Mekong River, distributed among15orders,49families and159genera. Among them there are114endemic species and100migratory species in it. The most species-rich families were Cyprinidae, Balitoridae and Cobitidae, accounting for35.09%,25.44%and6.14%of the species in the middle reaches of the Mekong River freshwater fish fauna, respectively. The middle reaches of the Mekong River was divided into34regions a ccording to the first order basin boundary. The Mun River and the Xe Bnagfai River hold the largest number of fish species, and the Xe Bnagfai River, the Se Bang Hiang River, the Nam Mun River and the Mun River have the largest number of endemic fish species.2) Se Bang Hiang River, Mun River, Nam Ngum River, Xe Bnagfai River and Tha Bo are higher in terms of species richness and diversity of fishes. The complexity of the mountainous provides a variety of fish habitat which gave birth to a higher diversity and more endemic species. The abundance of fish in the middle reaches is lower in the Mun River main stream which may be due to the foehn effect of the southern part of the basin and there are a lot of saline-alkali soils in the south of Khorat plateau.3) Based on the analysis of the fish community data, Mun River Basin was polylactic as a class lonely which means it has differences between these sub-basins. The tributaries of the left bank and the right bank tributaries in the northern Thailand roughly clustered into one group of the60%similarity. According to this principal component analysis of the environmental factors that we can conclude that the environmental factors can be divided into two principal components. The first principal component explains the altitude and temperature environmental factors and the second principal component explains the rainfall category environmental factors. Furthermore, according stepwise regression analysis between the environmental factors and the richness index, we obtained the correlation coefficient of the richness index and environmental factors is0.64(P=0.0017). Judging from the impact of richness, six variables are the annual precipitation (+), the precipitation of driest month (+), the basin area (+), annual mean temperature (+), the temperature annual range (-) sequentially.4) In the highest migratory fish abundance of migratory sub-basin, species numbers, richness and diversity of two migratory manners were peaks appeared in the April to September and October to February in next year. According to cluster analysis we can concluded that the migratory sub-basin were divided into there group. There were the Tonle Sap Lakes region, the Khong River, the Sang River and the Srepok River were unit one, the Nam Kading NBDC and the SongKhram River in the middle reach were unit two, and Phou Phanang NBDC and the estuary area are cluster into a group independently. The reasons for these differences may caused by estuary area contains more marine migratory fish and heterogeneity of the fish fauna in the upstream and downstream.5) According the migratory fish database of Mekong River, the migratory path of Pangasius genera was studied. This genera belongs distance migratory species. The Khone Falls played a certain role in the geographic barrier of the distribution of the Pangasius genera. The Srepok River, the Sekong River, the Sang River in the Cambodia and the Xayabury reach are the important feedlot and refuges for the Pangas/us genera.