17% of all protein eaten by people globally comes from fish, so naturally there is a high demand for it. As the human population increases, more fish will need to be fished for. Overfishing, however, has caused damage to aquatic ecosystems, and so fish farming aims to produce fish and reduce the overfishing of wild fish. Fish farming can be an issue for the captured fish, because the fish are kept in small pens where disease can easily be spread.