Abstract: A fish-growing cage, of the type having a central spar or other buoyancy chamber for deploying surrounding cage netting attached thereto, has a central spar configured in an elongated shape with at least two enclosed sections at opposite ends thereof in which buoyancy is altered by changes of air and water therein so as to cause a shift of center of balance of the cage that enables the central spar with the cage netting to be rotated and inverted. The cage can be raised from its normal submerged position to an emergent position where the top half can be subject to a maintenance operation, then submerged, inverted, and raised to the emergent position again so that the bottom half can be treated. The inverting cage facilitates cleaning of the netting and air-drying, and also allows for bath-treatment, crowding harvesting, or other handling of the fish.