It was clear that all local hatchery populations were contaminated with wild Thai Mekong populations regardless of population history, but they were not all contaminated by the Vietnam population. The proportion of NP-W found in the hatchery populations agreed well with the history of most populations; a remarkable proportion of NP-W was observed in SP and NR into which NP-W fish were intentionally introduced as broodstock ; the proportion was low in hatcheries without such a record of introduction (NI and HS)