Bjarne Kvinnsland has created a work based entirely on sounds from the inaccurately named “silent world”, with contributions from fish found in Norwegian waters - haddock, pike, cod and salmon. Sound production is not uncommon in fish. The sounds produced by fish with their swimming bladders often have particular functions - mating calls, warning calls, to express fear and so on. The haddock is a real chatterbox; cod produce low frequency grunts of about 50 Hz during the spawning season. Fish have no external ears, neither do they have hearing orifices like frogs. Fish do have a sort of ear, however, concealed in two pockets under the brain. Fish have developed hearing because the underwater world is not a silent one. Many types of fish use sound signals in the same way that birds use their song, such as to mark their territory or to threaten intruders. And every now and again, fish sounds can drive people round the bend.