title: Hemolymph chemistry and histopathological changes in Pacific oysters (Crassostrea gigas) in response to low salinity stress.
abstract: This study described seasonal differences in the histopathological and hemolymph chemistry changes in different family lines of Pacific oysters, Crassostrea gigas, in response to the stress of an abrupt change to low salinity, and mechanical grading. The most significant changes in pallial cavity salinity, hemolymph chemistry and histopathological findings occurred in summer at low salinity. In summer (water temperature 18°C) at low salinity, 9 (25.7% of full salinity), the mean pallial cavity salinity in oysters at day 3 was 19.8±1.6 (SE) and day 10 was 22.8±1.6 (SE) lower than oysters at salinity 35. Associated with this fall in pallial cavity salinity, mean hemolymph sodium for oysters at salinity 9 on day 3 and 10 were 297.2mmol/L±20(SE) and 350.4mmol/L±21.3(SE) lower than oysters at salinity 35. Similarly mean hemolymph potassium in oysters held at salinity 9 at day 3 and 10 were 5.6mmol/L±0.6(SE) and 7.9mmol/L±0.6 (SE) lower than oysters at salinity 35. These oysters at low salinity had expanded intercellular spaces and significant intracytoplasmic vacuolation distending the cytoplasm of epithelial cells in the alimentary tract and kidney and hemocyte infiltrate (diapedesis) within the alimentary tract wall. In contrast, in winter (water temperature 8°C) oyster mean pallial cavity salinity only fell at day 10 and this was by 6.0±0.6 (SE) compared to that of oysters at salinity 35. There were limited histopathological changes (expanded intercellular spaces and moderate intracytoplasmic vacuolation of renal epithelial cells) in these oysters at day 10 in low salinity. Mechanical grading and family line did not influence the oyster response to sudden low salinity. These findings provide additional information for interpretation of non-lethal, histopathological changes associated with temperature and salinity variation.
authors.affiliation: Fish Health Unit, Mt Pleasant Laboratories, Department Primary Industries, Parks, Water and Environment, Tasmania, PO Box 46, Kings Meadow, Tasmania 7249, Australia; National Centre for Marine Conservation and Resource Sustainability, University of Tasmania, Launceston, TAS 7250, Australia. Electronic address: Graeme.Knowles@dpipwe.tas.gov.au.
authors.forename: Graeme
authors.initials: G
authors.lastname: Knowles
authors.affiliation: Fish Health Unit, Mt Pleasant Laboratories, Department Primary Industries, Parks, Water and Environment, Tasmania, PO Box 46, Kings Meadow, Tasmania 7249, Australia.
authors.forename: Judith
authors.initials: J
authors.lastname: Handlinger
authors.affiliation: Murdoch University, School of Veterinary and Life Sciences, 90 South Street Perth, Western Australia 6150, Australia.
authors.forename: Brian
authors.initials: B
authors.lastname: Jones
authors.affiliation: National Centre for Marine Conservation and Resource Sustainability, University of Tasmania, Launceston, TAS 7250, Australia; School of Environmental and Life Sciences, University of Newcastle, Ourimbah, NSW 2258, Australia.
authors.forename: Natalie
authors.initials: N
authors.lastname: Moltschaniwskyj
mesh_terms: D000818:Animals; D006458:Hemolymph / Q000737:chemistry*; D010125:Ostreidae / Q000033:anatomy & histology / Q000737:chemistry*; D012965:Sodium Chloride / Q000032:analysis; D013312:Stress, Physiological
chemical_list: D012965:Sodium Chloride
keywords: Digestive gland; Grading; Kidney; Pacific oyster; Salinity; Stomach