A telemetry study of swimming depth and oxygen level in a Pangasius pond in the Mekong Delta

Ten Pangasianodon hypophthalmus were instrumented with depth and oxygen transmitters and released into a small-scale Pangasius pond in the Mekong Delta in Vietnam. The fish only exploited the upper-most 25% of the water column and frequently experienced severe hypoxia (< 20% air saturation) at night and at depths greater than 1 m below the surface, and with increasing hypoxia and anoxia towards the bottom. Aeration should decrease the amounts of toxic compounds present in the deeper water in the ponds (ammonia, nitrite, and possibly hydrogen sulfide) and thus make a greater proportion of pond volume available for the fish, allowing for higher stocking densities.