The impact of short-term hyposalinity stress on the Pacific oyster (Magallana gigas) infested with boring sponges (Pione vastifica)

This study investigates the effects of 16-h short-term hyposalinity stress on the functional state of hemocytes in the Pacific oyster Magallana gigas (Thunberg, 1793) infected with the boring sponge Pione vastifica (Hancock, 1849). We also studied pro-oxidant-antioxidant status, expression of genes associated with oxidative stress and heat shock proteins, growth arrest and DNA damage in the M. gigas mantle. Our results showed a significant increase of intracellular reactive oxygen species levels in hemocytes under exposure of salinity 5 psu and 10 psu. A decrease in salinity from 18 psu to 10 psu led to a significant increase in superoxide dismutase activity in bivalves mantle. However, no alterations in mitochondrial membrane potential in hemocytes, catalase activity, thiobarbituric acid reactive substance levels, gene expression of antioxidant enzymes, and heat shock protein expression in the mantle under low salinity exposure were observed. The changes in the prooxidant-antioxidant balance during sponge infestation under low salinity conditions indicate the development of oxidative stress in this mollusk. Heat shock proteins, which can protect bivalves against osmotic stress, did not show higher expression under sponge infestation and hyposalinity stress conditions.