Grass carp(Ctenopharyngodon idella)is one of the most important cultured fishes in China.During transportation in summer,massive mortality often occurs.As molecular chaperones,Hsps assist cells in their recovery from stress and promote cytoprotection.Limited reports described the expression of Hsps in grass carp at high temperatures,and the relationship between oxygen consumption,expression of heat shock protein and mortality needs to be investigated based on the oxygen- and capability- limited thermal tolerance theory(OCLTT)to further elucidate the thermal adaptation of this species to high temperature in view of integrated biology.In the present study,the expressions of hsp70 and hsp90 after rapid temperature increase were studied.Grass carps were acclimated at 20 ℃ and then exposed to designated temperatures(20,22,24,26,28,30,32,34 ℃)for 3 h heat shock.After 2 h- recovery at 20 ℃,liver,muscle and gill of tested fish were sampled and hsp70 and hsp90 were determined using semi-quantitive real time PCR.Expression of hsps increased with temperature increase until 32 ℃ in muscle and gill,and then decreased at 34 ℃.In liver,expression of hsps kept increasing in all temperature treatments.These results indicated that hsp70 and hsp90 were sensitive to temperature increase in grass carp.Analyzed heat shock proteins data with previous results of oxygen consumption and lethal temperatures of grass carp,the physiological adaptations of grass carp could be explained by oxygen and capability- limited thermal tolerance theory(OCLTT),which pointed out that the imbalance between oxygen demand and tissue oxygen supply ability was the primary factor which limited organisms’ thermal tolerance and the ability of aerobic metabolism greatly limited the survival of organism beyond critical temperatures.With temperature increase,the maximum value of oxygen consumption in grass carp occurred at 28 ℃,and then the oxygen consumption decreased when temperature was beyond 28 ℃,indicating a transformation from aerobic metabolism to anaerobic metabolism at this critical temperature.The expressions of heat shock proteins kept increasing until 32 ℃ in muscle and gill in grass carp,and provided defense against high temperature.However,this protection of heat shock proteins was limited and then death occurred when temperature was beyond 32 ℃.The change of metabolism,increase of oxygen free radicals and the consumption of energy due to stress proteins synthesis of grass carp were closely related to the decrease of capability of immune response when water temperature was beyond 28 ℃.In general,high water temperature could alter the metabolic pathway,induce heat shock protein expression,reduce immune response,and then cause large scale mortality.Therefore,appropriate ways should be applied to maintain water temperature under 28 ℃ to avoid large-scale mortality during transportation.