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The effects of three environmental factors,salinity,carbonate alkalinity,and pH,on the survival,feeding,and respiratory metabolism of Eogammarus possjeticus (Amphipoda: Gammaridae) were investigated experimentally.The results show that E.possjeticus could tolerate a broad salinity range.The 24-h lowest median lethal salinity was 2.70,and the highest was 47.33.The 24-h median lethal alkalinity and pH were 23.05 mmol/L and 9.91,respectively;both values decreased gradually with time.Different values of salinity,carbonate alkalinity,and pH resulted in significant differences in the cumulative mortality (P＜0.05).The ingestion rate and feed absorption efficiency were significantly affected by the coupling of the three environmental factors (P＜0.05).With increases in carbonate alkalinity,salinity,and pH,both ingestion rate and feed absorption efficiency exhibited a downward trend,indicating a decline in feeding ability under high salinity and more alkaline water conditions.The coupling of salinity,carbonate alkalinity,and pH also had a significant effect on respiration and excretion (P＜0.05).The oxygen consumption rate increased first and then decreased with increasing carbonate alkalinity.Under the same carbonate alkalinity values,the oxygen consumption rate increased with increasing salinity.Under the same carbonate alkalinity and salinity,the oxygen consumption rate initially increased and then decreased with increasing pH.The O∶N ratio first increased and then decreased with increasing carbonate alkalinity.When carbonate alkalinity was less than 6 mmol/L,the O∶N ratio increased with increasing salinity and decreased with increasing pH.The results demonstrate that changes in salinity,carbonate alkalinity,and pH had a measurable impact on the osmotic pressure equilibrium in E.possjeticus and affected the energy supply mode (i.e.ratio of metabolic substrate).