The effects of non-lethal heat-shock-induced cross-protection on survival and growth of Pacific whiteleg shrimp, Litopenaeus vannamei in response to ionic stress in inland saline waters

Abstract

Non-lethal heat shock (NLHS) was used to enhance tolerance to other stressors in aquatic organisms and its effects are associated with the accumulation of Hsp 70. A study was conducted to determine the effect of NLHS on the cross-protection of L. vannamei against stress in K+-deficient inland saline water. To determine the NLHS based on mortality and gill heat shock protein 70 (Hsp70) abundance, L. vannamei juveniles (3.52 ± 0.23 g) were reared in inland water of 10 ppt salinity with 100% seawater equivalent (SWequ) K+ fortification. As one hour of heat shock at 36 °C resulted no mortality and a 3.5-fold increase in Hsp70 protein in gills when followed by 8 h recovery at 28 °C, the 36 °C was designated as NLHS. Subsequently, P. vannamei juveniles (4.64 ± 0.01 g) were exposed to 1 h NLHS in inland saline water containing 25%, 50% and 75% of SWequ K+ in triplicates following a recovery of 8 h, whereas the control group did not receive NLHS. The NLHS significantly increased Hsp70 protein in the gills and muscle. In addition, NHLS brought about higher catalase and superoxide dismutase activity in the gills and hepatopancreas, along with increased serum glucose levels. Increased Hsp70 protein abundance in muscle and gills remained elevated even after 12 h exposure to varying K+ levels, conferring cross-protection by NLHS against ionic stress caused by K+ depletion in inland saline waters. A 45-day growth study showed a significant increase in weight gain and survival (%) in NLHS groups compared to the control group, irrespective of the K+ fortification. This growth-promoting effect of NLHS was also evident in the group reared in the most K+ deficient inland saline water. This study shows that NLHS provides cross-protection through accumulation of Hsp70 protein and activation of antioxidant enzymes, in K+ deficient inland saline water, promoting shrimp growth and survival with atleast 50 aqueous K+ supplementation.