The aetiology of environmental stress responses and disease in bivalve molluscs

The aim of this study was to provide a comprehensive set of quantitative and qualitative baseline responses at physiological, metabolical and immunological levels, in the Pacific oyster Crassostrea gigas (Thunberg), the European flat oyster Ostrea eduli (L.), and the Manila clam Tapes philippinarum (Adams and Reeve). The energetics of these species were compared across a matrix of temperature and salinity conditions. Field trials examined the effect of exposure of three O. edulis populations to infection by the protozoan parasite Bonamia ostreae, and enzyme electrophoresis investigated the genetic basis for any differences. Changes in immunocompetence were monitored from field samples and with controlled Vibrio anguillarum bacterial challenges. Haemolymph and haemocytic responses were recorded.Filtration rate had the most significant effect on scope for growth (SFG) indices measured in all species. C. gigas showed a much wider range of filtration rates than O. edulis and consequently had much higher SFG. Optimum environmental conditions for C.gigas occurred at 20-25oC and 19-25�, compared with 20oC and 33� for O. edulis, and 15-20oC at 33� in T. philippinarum. Separate winter and summer physiological behaviour was detected in C. gigas and O. edulis, with the change occurring at 15oC and 10-12oC respectively. Body condition indices were inversely proportional to SFG and were probably related to the reproductive cycle. Temperature was shown to have the most significant influence on energetic factors, with salinity having little effect.Field trials investigating Bonamia effects in three O. edulis populations found a significant, inverse size relationship with most of the physiological measurements.