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The suspension-feeding sea cucumber Cucumaria frondosa has become commercially important in recent years.Finding proper diets is the fi rst important step for intensive aquaculture of this sea cucumber.In this study,adult C.frondosa were exposed to one of the following diet treatments: control(no diet provided),two powdered seaweeds(Ascophyllum nodosum and Saccharina latissima),a commercially available microalgal diet(shellfi sh diet)and natural seston.The effects of diets on the feeding behavior and physiological properties of sea cucumbers were investigated after a 5-week rearing period.Results show that sea cucumbers fed with shellfi sh diet exhibited a signifi cantly higher tentacle insertion rate(1.80± 0.20 insertion/min)than these fed with seaweed powders,and there was no signifi cant different between the two groups fed by seaweed powders.No signifi cant difference was found on the fecal production rate among the feeding groups.The minimum oxygen consumption rate was observed in the control group(5.76±0.99 μg O2/(g.h)),which is significantly lower than individuals fed with A.nodosum,shellfish diet,and natural seston; however,no significant difference was shown between those of control and S.latissimi groups.The maximum ammonium excretion rate was found in the A.nodosum group(0.03±0.01 μmol/(g.h)),which is signifi cantly higher than other groups.The minimum O/N ratio was observed in the A.nodosum group(14.57±1.04),which is significantly lower than the S.latissima,shellfish diet,and natural seston groups.Individuals fed with seaweed powders had similar physiological properties with these fed with microalgae diet and natural seston,indicating that A.nodosum and S.latissima can be explored as promising diets for intensive aquaculture of C.frondosa.