Spatial Variations in Fish Abundance in the Mekong Delta

— For the first time, the density of fish population has been quantitatively assessed in the Mekong River delta in the territory of the Socialist Republic of Vietnam. The studies were carried out in the main courses of two main branches, Hau and Tien rivers, into which the Mekong River splits in its lower course, and in the mouth branches of the delta. When comparing the fish abundance at 28 stations of the delta, statistically significant differences in the average specific abundance were found between the main river course and a mixohaline zone of the estuarine ecotone where values of the fish abundance were much lower. The analysis of the relationship between the fish abundance dynamics and different natural and anthropogenic environmental factors has demonstrated a weak significant correlation with salinity, distance from the mouth, the type of fish community and the amount of anthropogenic debris on the bottom. Large fluctuations in the fish abundance parameters associated with aggregated distribution of such species as Polynemusmelanochir , Ariusmaculatus and some representatives of the families Akysidae, Cynoglossidae, and Ariidae are observed in the delta. The results may be used as a baseline for subsequent monitoring of the abundance dynamics of bottom-dwelling fish communities in the Mekong Delta.