The International Center for Living Aquatic Resources Management (ICLARM) and its research partners have recently developed a genetically improved Nile tilapia strain. This paper analyzes the potential impact of culturing the improved tilapia strain in five Asian countries (Bangladesh, China, the Philippines, Thailand and Vietnam), using a three-step procedure. The steps are (1) to develop a model of the fish sector for each country using data from baseline surveys of producers and consumers and from secondary sources, (2) to construct ex ante impact indicators using data collected in on-farm production trials, and (3) to analyze the impact of the use of the genetically improved Nile tilapia by incorporating the results of on-farm trials into the fish sector model. The analysis indicates that the use of the genetically improved strain will benefit both producers and consumers of fish.