To feed the growing human population, more land will need to be devoted to the cultivation of food and cash crops and, being a finite resource, this will reduce its availability for pasture and fodder, as has already occurred in Asia (Table 2). On the other hand, increased food and cash crops will make available more crop residues and agro-industrial by-products, many of which represent valuable animal feed resources for which there is known technology to support increased levels of production. It is clear that, in order to maintain food production, the efficiency of resource utilization must be increased and alternatives - such as marine and freshwater fish culture - must be developed.