Italian demand for organic products is rapidly increasing, yet there is currently no supply of certified organic marine-fish. Moreover, over recent years marine fish farm profitability has been reduced because of competition from imported products. A pilot project was carried out in order to: a) define standards for organic marine fish farming; b) evaluate production costs in four farms, experimenting semi-extensive organic fish farming under proposed standards (seabream, Sparus aurata and seabass, Dicentrarchus labrax); c) estimate the potential demand for certified organic marine fish and consumer willingness to pay in order to figure out the profitability of a product differentiation strategy. This paper shows the economic results for production costs at the farm level and potential demand. The latter has been estimated using survey-data of 6,877 consumers by means of a questionnaire-interview carried out during an experimental organic marine fish promotion sale. Results show that organic marine fish farming could be a good market opportunity for some Italian fish farmers by improving consumer information on organic products, adopting a supply concentration strategy at the farm level and carefully managing semi-extensive-farming set up by proposed regulations.