Device for lowering and raising a fish rearing unit

A device for lowering and raising a rearing unit, said rearing unit being provided with a float collar comprising an inner and an outer floating ring which floating rings have hollow interiors, and are normally water tight, so that the rearing unit floats on the water surface, and at least one of the floating rings is equipped with at least one fluid tight partition wall, at least a first air leading means and a second air leading means are arranged on at least one of the floating rings in order to let air out of the floating rings as they are lowering, and into the floating rings as they are raising, which air leading means are connected to at least a first connecting tube, arranged to lead the air respectively from and to the floating rings, and the floating rings are equipped with water filling openings, characterized by water control means for the introduction and removal of water at the water filling openings, said water control means having a valve mechanism, said water control means being situated on the inner and outer floating rings, respectively, so that water can be let into the floating rings for lowering, and out of the floating rings for raising, as air pockets are formed between admitted air and the at least one partition wall,

• a second connecting tube is arranged to lead the air respectively from and to the floating rings, wherein the first connecting tube is connected to a first air pocket and the second connecting tube is connected to a second air pocket, and that the first air leading means and second air leading means are situated in a mirror symmetric manner about a diametral axial plane through the at least one partition wall and the water control means.