To evaluate the physiological responses and changes of swimming crab,Portunus trituberculatus between pre- and post-maturity at different salinities(15,20,25,30 and 35),the oxygen consumption rate(OCR),ammonia excretion rate(AER)and respiratory enzyme activities including hexokinase(HK),pyruvate kinase(PK),succinate dehydrogenase(SDH)and lactate dehydrogenase(LDH)were measured in this study.Results showed that the interaction of salinity and size did not influence the respiratory metabolism significantly.Salinities had a significant effect on AER other than OCR.Marked differences were found in both OCR and AER between pre and postmaturity individuals(P<0.05).No significant difference of O∶〖KG-*2〗N ratio was found among different salinities(P>0.05),however,O∶〖KG-*2〗N ratio in prematurity individuals was significantly higher than that in postmaturity individuals(P<0.05).It was noticed that the activity of HK and PK changed significantly with size rather than salinity(P<0.05).Excluding LDH,no significant correlation between respiratory metabolism enzymes and salinity was observed(P>0.05).However,the respiratory enzymes in tested tissues changed significantly between pre and postmaturity(P<0.05)except SDH and LDH in gills(P>0.05).The study indicated that compared to salinity,body size more impacted the respiratory metabolism of P.trituberculatus.And it is suggested that long-term salinity acclimatization could lower or eliminate the difference of respiratory metabolism ofP.trituberculatusat different salinities.