Effects of the muscle relaxant, magnesium chloride, on the Sydney rock oyster (Saccostrea glomerata)

The effects of the muscle relaxant magnesium chloride (MgCl2) were monitored in the Sydney rock oyster, Saccostrea glomerata, under laboratory conditions. The relaxant was first tested for efficiency and then for potential deleterious effects on immunological and spawning activity. A range of immunological parameters were tested including, total haemocyte frequencies, acid phosphatase, superoxide and phenoloxidase activities in the haemolymph, as well as total haemolymph protein levels. All of the oysters exposed to MgCl2 demonstrated total relaxation within 6h of the initial exposure. Total haemocyte frequencies, acid phosphatase activity and superoxide activity all increased significantly during the first 48h after exposure to the relaxant but declined later. Phenoloxidase activity increased immediately after relaxation but then decreased consistently until 48h after exposure. Overall, the data indicate that MgCl2 is an effective relaxant for use on S. glomerata, and that any potentially deleterious effects of the relaxant do not persist for more than 96h.