The majestic Mekong River passes through Cambodia territory, spanning approximately 480 km, connecting between Southern Laos PDR to Northern Vietnam’s southern hemisphere. The river serves as one of the busiest water migratory routes in the world. Each year, billions of fish of all shape and sizes travel up and down this river into deep water habitats in Tonle Sap river, making it one of the most fascinating animal movements on earth.

Around September and October, some of freshwater giants begin to embark on their migratory journey down the flooded Tonle Sap lake, which is the largest in Southeast Asia, into the Tonle Sap river and then the Mekong. Super-sized fish including the Mekong giant catfish, and the giant barb, both of which can grow up to 3.04 meters and weigh around 272 Kilogram per head. The giant barb is largely regarded as the national fish of Cambodia.

After this in around January, hundreds of species of other small fishes begin the same journey down the lake into the two rivers where they will eventually breed and produce young fishes that will travel back into the Tonle Sap river during the dry season as the Mekong river water level rises.

Fishes that travel back into Tonle Sap will remain in deep pools, confined and deep areas within river channels, where young fish can grow ten times their original dry-season size. During the dry-season these deep-water areas serve as nurseries and refuge for both big and small fishes.