Swimming performance is an integrated index of fitness in fish.It is fundamental for the fish’s ecology and behavior.Perfluorooctane sulfonate (PFOS) is a persistent and ubiquitous environmental contaminant that has been found to pose various risks to fish health and the safety of aquatic ecosystem.However,little toxicological research has sought to the effects of PFOS exposure on swimming performances of fish.Experiments were carried out to clarify the impacts of acute exposure to PFOS on the swimming performances and metabolic rate in female topmouth gudgeon (Pseudorasbora parva),to understand the underlying ecotoxicological effects of waterborne PFOS exposure on fish physiology and behavior.The fish were exposed for 96 h to 0,0.5,2,8 or 32 mg/L PFOS from a stock solution prepared with dimethyl sulfoxide (DMSO) as a solvent.Afterwards,the routine metabolic rate (RMR),spontaneous swimming behavior (SSB),fast-start swimming performance (FSP) and critical swimming speed (Ucrit) of the topmouth gudgeon were examined.The results show reduced behavioral performance and increased physiological stress with increasing PFOS concentration.Both RMR,SSB and Ucrit were significantly affected by PFOS exposure (P<0.05).Swimming distance reduced (P=0.045) and proportion of motionless time increased (P=0.032) in topmouth gudgeon under PFOS exposure.The lowest observed effect concentration (LOEC) is 2 mg/Lfor SSB.Besides,PFOS imposed visible physiological stress on fish,resulted in increased RMR(P=0.001) and decreased Ucrit(P=0.005),whereas the FSP-related parameters were not influenced by PFOS exposure(P>0.05).The overall results indicate that the anaerobic swimming capacity was conservative,but the metabolic level,spontaneous behavior and aerobic swimming performance in topmouth gudgeon were susceptible to PFOS contamination,and hence might be useful as considerable potential indicators of pollution.