Nam Theun 2 is the largest neo-reservoir in Lao PDR that was impounded to produce electricity. The objective of this study was to assess the input of the offshore zone to the total fish production. Hydroacoustics in areas > 5 m deep were sampled during the cold-dry season for 2 consecutive years. Results showed low fish densities (200-300 ind. ha(-1)), low biomass ( < 1 kg ha(-1)) and fish of small sizes (approximately 6 cm) in deep zones. Fish stock in the pelagic zone was concentrated between 2 and 13 m depth. The low colonization by fish was corroborated by the small catches achieved by experimental fishing in this part of the reservoir. This study has highlighted the limited contribution of the pelagic zone of a large neo-reservoir to fish production (low density, low biomass and few commercial species) when the reservoir was at its maximal water level. This study suggests that future management actions should mainly focus on the littoral zone.