Abstract: A coupling 1, 50, 100 for joining adjacent frame members 2, 3 of a fish breeding enclosure 5 comprises a first mounting means 10, 52, 105, 106 for mounting to one frame member 2, a second mounting means 11, 53, 105, 106 for mounting to another frame member 3 and a flexible body 12, 51, 101 of elastomeric material between the first and second mounting means 10, 11, 52, 53, 105, 106. The coupling 1, 50, 100 constrains relative rotational and translational movement between the frame members 2, 3 in use to a predetermined level which is determined by the material of the flexible body 12, 51, 101 and/or by mechanical limit stops 62, 63. A non flexible connection such as a rod 35 having flanges 36, 37 or a chain 90, 110 provides a mechanical connection between the mounting means 10, 11, 52, 53, 105, 106 in the event of failure of the flexible body 12, 51, 101.