Aquaculture apparatus includes an elongate tube of flexible translucent plastic material which extends longitudinally along level ground. The tube is inflated and air supported. At least the lower section of the tube defines a water course. The tube is closed at both ends to form a water enclosure. A number of such tubes are arranged in side-by-side relation and are covered by a plastic sheet cover layer. The cover provides an air gap to insulate the inner tubes and restrict heat loss. The tubes are used to form at least some of the modules of an aquaculture system for rearing fish and/or for effluent, waste or water treatment.