Abstract: A fish cage for use in water comprising a main part (1) made of a watertight, substantially rigid material and has an outlet for effluent (12). The main part (1) is substantially hemispherical, and may slip unhindered through the water along a spherical path without influencing the body of water inside the cage substantially. Because the forces acting on the main part (1) from the surrounding water act mainly along the shell as opposed to perpendicular to the shell, the risk for tearing and the risk for swashing are reduced. Embodiments having flow and lighting conditions adaptable to different species are also disclosed. The cage can be localized in areas with currents and waves, and it can easily be adapted for different species.

Abstract: There is provided a method for preventing the occurrence of abnormal behavior such as cannibalism, fright behavior and collision death during rearing, storage and transportation of tuna of larva, juvenile and young adult fish stages, particularly, of those periods in the seed production. The abnormal behavior during rearing, storage or transportation of tuna is prevented by controlling their visual stimuli, particularly, by making wall and bottom surfaces of a rearing water tank coming with contact with the environment transparent, setting a visual stimulus-buffering material through which light transmits partially in both straight and diagonal directions, maintaining the tuna in the presence of colored fine particles in the environment, or controlling the fluctuation in illumination of the environment, or a combination thereof. Alternatively, death of tuna due to collision with a rearing water tank wall is prevented by stimulating their visual sense.

Abstract: A floating artificial weed line which attracts fresh or salt water fish. The invention is made of floating material preferably in the form of multiple floating panels connected together to form weed lines of any desired size. The panels are framed by a floating plastic water resilient structural material filed with a plastic material resembling sea weed. The weed lines can be used drifting or anchored to the bottom, and may be connected to a fishing boat.