The effects of salinity on the interaction between a pathogen (Listonella anguillarum) and components of a host (Ostrea edulis) immune system

Data are presented from a study to determine how salinity may modulate the interactions between an opportunistic bacterial pathogen Listonella anguillarum and the immune system of a bivalve host, the European flat oyster Ostrea edulis. Oysters were acclimated to three salinity regimes (32, 25 and 16 parts per thousand, at 15 degrees C) for 7 days within the laboratory and were then inoculated with a sub-lethal dose of live L. anguillarum. Forty-eight hours after inoculation measurements were made of the changes in haemocyte composition, haemolymph hydrogen peroxide concentration and haemolymph lysozyme activity to provide information on both the cellular and humoral components of the immune system. The data indicated that in the majority of cases the effects on the immune system were dose dependent. At 32 parts per thousand, a salinity which promoted the growth of the bacterial inoculate, there was a significant increase in the number of circulating large granulocytes and a significant decrease in the haemolymph hydrogen peroxide concentration. At lower salinities, which were less favourable to the growth of L. anguillarum, there were no significant immune system effects. The data highlight the potential for environment management as a tool in controlling opportunistic pathogens and subsequently disease in commercially important bivalve species. (C) 2000 Elsevier Science Inc. All rights reserved.