Combined effects of acute thermal and hypo-osmotic stresses on osmolality and hsp70, hsp90 and sod expression in the sea cucumber Apostichopus japonicus Selenka

The combined effects of acute temperature and salinity on osmolality, expressions of heat shock proteins mRNA (hsp70, hsp90a and hsp90b) and superoxide dismutase mRNA (sod) were investigated in the sea cucumber Apostichopus japonicus Selenka. There were 12 treatments (combinations of temperature at 16, 20, 24 and 28 °C and salinity at 22, 27 and 32 ppt). In low salinity environments, the osmolality of the sea cucumber’s coelomic fluid decreased immediately and reached osmotic balance within 6 h. The decline of osmolality after 2 h of hypo-osmotic stress was faster at high temperatures (28 °C) than that at low temperatures (16 and 20 °C). Cellular level stress was indicated by up-regulation of hsp70, hsp90s and sod mRNA, and the maximal expression of all genes occurred at 6 h after stresses. The up-regulation of hsps and sod mRNA indicated the emergence of protein denaturation and oxidative damage and also suggested an increase in energy consumption at high temperature and low salinity. These results indicated that high temperature and low salinity could change biochemical pathways and energy budgets and then potentially impair the osmoregulation of the sea cucumber. Therefore, effective ways should be taken (e.g., draining off the upper freshwater, exchanging water and adding man-made sea water) to prevent the damage to sea cucumber culture caused by low salinity induced by rainstorms, especially at high temperature.