title: Effect of acute salinity stress on ion homeostasis, Na+/K+-ATPase and histological structure in sea cucumberApostichopus japonicus.
abstract: BACKGROUND
  Sea cucumbers (Apostichopus japonicus) are an imperiled fauna exposed to a variety of environmental condition such as salinity and studies are urgently needed to assess their effects to guide aquaculture efforts. The effects of acute salinity stress on coelomic fluid osmotic pressure, ion concentrations, the activity of Na+/K+-ATPase in respiratory trees and the histological variations were measured to evaluate the salinity tolerance of sea cucumbers.
  
  
  RESULTS
  Significant correlations in osmotic pressure were observed between coelomic fluid and ambient environmental salinity. In coelomic fluid, Na+concentration was observed fluctuated during salinity 18 psu and the inflection point presented at the 6 h. The Na+/K+-ATPase activity in respiratory trees indicated the "U-shaped" fluctuant change and the change trend was opposite with the Na+concentration. The ions (K+, Cl-) concentration decreased and showed the same tendency at salinity 40 psu with salinity 18 psu. The total coelomocytes counts and phagocytosis of coelomic fluid Na+/K+-ATPase activity indicated fluctuating changes under different salinity stress. Histological variation revealed a negative relation between decreasing salt concentration and tissue integrity. Tissue damages were significantly observed in intestines, muscles and tube feet under low salinity environment (18, 23 and 27 psu). The connective tissue in intestines ofA. japonicusexposed to 18 and 23 psu damaged and partly separated from the mucosal epithelium. The significant variations occurred in tube feet, which presented the swelling in connective tissue and a fracture in longitudinal muscles under low salinity (18 psu). The morphological change of tube feet showed the shrinkage of connective tissue under high salinity (40 psu). The amount of infusoria in the respiratory trees decreased or even disappeared in salinity treatment groups (18 and 23 psu).
  
  
  CONCLUSIONS
  The results inferred that osmoconformity and ionoregulation were seen in sea cucumbers, which contributed to understand the salinity regulatory mechanisms ofA. japonicusunder acute salinity stress.
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023 China.
authors.forename: Chenfan
authors.identifier: 0000-0002-1916-6487
authors.initials: C
authors.lastname: Geng
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023 China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Tian
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023 China.
authors.forename: Yanpeng
authors.initials: Y
authors.lastname: Shang
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023 China.
authors.forename: Liqiang
authors.initials: L
authors.lastname: Wang
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023 China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023 China.
authors.forename: Yaqing
authors.initials: Y
authors.lastname: Chang
keywords: Coelomic fluid; Histological structure; Ion concentration; Osmoregulation; Salinity; Sea cucumbers