Induced thermotolerance of Cyprinus carpio fingerlings following non-lethal heat shock

Abstract

This study examined the effects of a non-lethal heat shock (NLHS) towards resistance of a subsequent lethal heat stress or in other words, induced thermotolerance (ITT) of the common carp, Cyprinus carpio fingerlings. Prior to testing the ITT, the lethal heat treatment (LHT) of this species was determined. Fish acclimatized at 28°C were heat shocked to 34°C, 36°C, 38°C, 40° C and 42° C for 30 min, and given a subsequent recovery of24 h at 28°C. The survival was determined after 24 h by counting actively swimming animals. Mortality was not observed when fish were heated to 36°C. A slight decrease in survival occurred when fish were exposed to 38°C while 39°C resulted in 50% mortalities, the latter characterized as LT 50. Heat shock at 41 °C killed all animals indicating that this temperature was lethal and thus was considered as the lethal heat treatment (LHT). To test ITT, fingerlings were exposed from 28° C to NLHS of 32° C, 34° C, 36° C and 38°C for 30 min and given a recovery of 8 h. Fingerlings were exposed to LHT for 30 min to determine whether thermotolerance is induced. It is found that all NLHS temperatures confer tolerance of fingerlings against LHT compared to those of the non-heat shocked controls, where total mortalities occurred in the latter treatments. The highest protection was achieved at 38 °C, with an approximately 43% survived incubation, perhaps due to the upregulation of heat shock proteins, a group of protein that are responsible for protection against extreme forms of stress. Further studies such as immunoblotting are required to substantiate the putative role ofHsps on ITT of Cyprinus carpio.