A self-propelled underwater fish cage developed and recently tested by an MIT researcher may provide a way for fish farming to move out onto the open ocean.
(Giant self-propelled fish farm video)
Cliff Goudey, director of MIT Sea Grant's Offshore Aquaculture Engineering Center, is exploring a different approach to moving the cages. By placing large, slow-turning propellers directly on a cage, Goudey frees it from the normal constraints of a boat. His system uses a pair of eight-foot diameter, electrically powered propellers, with 6.2-horsepower underwater motors. The motors are powered through tethers to the surface attached to a diesel generator and a pair of motor controllers mounted on a small boat.
Recently he tested the approach at Snapperfarm Inc., an offshore fish farm in Culebra, Puerto Rico, that grows cobia in submerged cages. By fixing a pair of the propellers to the mid-depth of a 62-foot diameter Aquapod® fish cage in a horizontal line 9 feet apart, Goudey maneuvered the cage as well as any boat-based system.
Mobile fish cages could solve a variety of problems related to fish farming in the open ocean. The limiting factor in the number of fish that can be raised in a cage is often the oxygen content of the water during slack water. A moving cage could ensure a steady supply of fresh water.
Fish farming, in the sense of raising fish in a land enclosure for food, has been around for centuries. Mariculture, the raising of fish for food in the open ocean, is only a few decades old.