ClosedFishCage will focus on the development of a closed, escape proof, constant volume, sea-based cage for fish farming. Among the project’s innovative elements are a very durable and flexible polymer plastic net pen, a predator guard, a control system, easy set-up and replacement of damaged cage parts. The technological solutions involved in the sea-based cage will preserve advantages of land-based fish farming while at the same time taking advantage of the cost efficiency of seabased fish farming. Furthermore, the new cage system will be both substantially more cost-efficient and also more environmentally friendly existing fish farming technologies. Consequently, ClosedFishCage will result in the development of new, more appropriate technology enabling increased use of sea-based fish farming and thus also greatly improve possibilities of fish farming technology. The market for fish, and especially European farmed fish, continues to grow. However, EU catches have dropped in recent years, aquaculture production has remained stable, and the current supply of fish is therefore not enough to cover market demand. Furthermore, as a result of a combination of near depletion of certain EU fishery stocks, reduced annual catch quotas, and reduced fishing fleets, Member States of the Union are becoming increasingly dependent on imports from third countries. ClosedFishCage will not only improve the competitiveness of SMEs in the aquaculture sector but also safeguard the potential production of good quality fish, in sufficient quantities, at competitive prices.