Abstract
BackgroundSea 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.ResultsSignificant 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 of A. japonicus exposed 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).ConclusionThe results inferred that osmoconformity and ionoregulation were seen in sea cucumbers, which contributed to understand the salinity regulatory mechanisms of A. japonicus under acute salinity stress.
Highlights
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
Physiological indexes in A. japonicus exposed to different salinities Through the acute salinity stress, all experimental sea cucumbers survived under all salinity treatment
When the salinity was maintained at 40 psu for 12 and 48 h, the osmotic pressures in coelomic fluid were 1182.0 ± 5.0 m Osmol kg−1 and 1183.7 ± 4.3 m Osmol kg−1, respectively, which showed no significant difference with the ambient water osmotic pressure (12 h, 1180.0 ± 0.6 m Osmol kg−1; 48 h, 1178.3 ± 1.2 m Osmol kg−1)
Summary
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 sea cucumber (Apostichopus japonicus) is a representative economic marine organism due to its potential as an edible delicacy as well as a traditional Chinese medicine, which widely distributed in coastal areas of tropical and temperate zone (Yan et al 2013; Yu et al 2014). Sharp salinity changes may affect the feed intake and higher energy utilization for osmoregulation resulting in poor growth of sea cucumbers, and can even lead to discharge intestine and death (Fankboner 2002). Salinity had significant impacts on sea cucumbers, affecting their metabolism, growth and survival (Vidolin et al 2002; Fankboner 2002). Understanding sea cucumber’s regulating mechanism against abiotic stressors may provide insights to the evolution of the stress response systems in holothurid invertebrates
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