Fisheries products found in the landing places or markets usually represent a fraction of what has been originally taken out from the sea by fishermen. A more or less variable amount of the gross (or overall or initial) catch, in fact, is returned either dead or alive to the sea for multiple reasons. This phenomenon, generally known as 'the discard problem', has raised more and more global concern especially in the last decades since introducing more selectivity gears and acquiring more reliable catch data (also about the survival rate of the discarded specimens) are considered basic requirements in the current management plans for recovering and rebuilding fish stocks. To this concern, the current Common Fisheries Policy aims to reduce the discard rate in the European waters through the introduction of a landing obligation (better 'discard ban') according to which all the specimens of the 'target' stock caught must be landed. This chapter focuses on the characterization of the catch returned to the sea 'potential' available to be landed after the introduction of landing obligation, and the possible use as a potential food source in aquaculture (the direct use for human consumption is in fact prohibited).