There is ample evidence that, when properly conducted, especially as a business (commercial) activity, aquaculture can make significant contribution to national food security, poverty alleviation and economies, factors which often determine policy makers' support to any sector. Yet, quantitative evaluation of these merits is poorly documented, particularly in developing countries, which often limits the much needed political and financial support to the sector for its adequate development. This paper suggests to measure aquaculture's contribution to a country's economy through the "aquaculture employment multiplier". While the document refers to "commercial aquaculture" throughout, the methodology developed can be applied to aquaculture in general.