This research is to determine the economic performance of the Pangasius farmed in Vietnam and seabass-seabream farmed in Mediterranean countries based on Data Envelopment Analysis (DEA), which is used to decompose productivity into changes in scale efficiency and technical efficiency. Data for 20 pangasius producers and 13 production companies of seabass and seabream during the period of 2009-2014 are available for the analysis. The result shows pangasius firms have performed at a low technical efficiency. Under the assumption of variable-return-to-scale (VRS), we found that the average technical efficiency (TE) for pangasius amounted to only 0.677, implying that the Vietnamese pangasius firms included in this study could have reduced inputs by 32.3% while maintaining the same level of output. In general, Vietnamese pangasius firms operated far below the efficiency frontier. This farming could gain an efficiency of 14.5% on average by taking better advantage of the existing economies of scale. On the other hand, technical and scale efficiency of seabass and seabream firms are low and have not improved much in recent years. The technical efficiency scores under CRS averaged only 0.429, indicating that seabass and seabream firms could have reduced inputs by 57.1% while maintaining the same level of output. Calculated scale efficiency is 0.605, implying that firms could, on average, reduce input by almost 40% by taking better advantage of their economy of scale opportunities. Interestingly, no firm in the sample was found to be operating at the scale optimal level.