The effects of stressors on the dynamics of Bonamia exitiosus Hine, Cochennec-Laureau & Berthe, infections in flat oysters Ostrea chilensis (Philippi)

Oysters, Ostrea chilensis, infected with Bonamia exitiosus were held under stressful conditions for 14 days, and then under normal conditions for 3.5 months, to determine the affects of stress on B.exitiosus infection levels. The stressors used were (1) air exposure for 8 h daily; (2) hot water (25–26 °C), or (3) cold water (7 °C) for 1 h daily; (4) hyposaline (15‰), or (5) hypersaline (39–40‰) water; (6) starvation in filtered sea water; and (7) vigorous stirring four times a day. A control tank held oysters in static sea water, which was changed daily. Oysters were also (8) kept in a trough among heavily infected oysters (trough exposure), or (9) in a trough without other oysters (control), for 4 months. Oysters in hyposaline conditions all died within 3 weeks, but this was apparently unrelated to Bonamia infection. Otherwise, cumulative mortalities were highest in trough exposure, cold, hypersaline and hot treatments. There was a significant difference in prevalence between treatments, and the stir, hot, cold, hypersalinity and trough exposure treatments had significantly higher intensities of infection than controls. The mean intensity of Bonamia infection was significantly higher among female and spent oysters than in male and hermaphrodite oysters.