ABSTRACT: Assimilation efficiency (AE) of metals from ingested food is critical for understanding trace metal accumulation and trophic transfer in aquatic animals. Most recent measurements of metal AEs have been on aquatic invertebrates, whereasrelatively few studies have examined metal assimilation in fishes. In this study we determined the AEs of Cd, Cr and Zn in 2 fishes (pelagic glassy Ambassis urotaenia, Ambassidae, and the intertidal mudskipper Periophthalmus cantonensis,Gobiidae) feeding on 2 zooplankton prey (brine shrimp Artemia larvae and copepods). Zooplankton were radiolabeled either by feeding on radiolabeled phytoplankton or by direct exposure to radiotracers in the dissolved phase. Fishes were then fedwith radiolabeled zooplankton prey for <1 h, and the retention of ingested metals in the fishes was followed for 2 d. The measured AEs of Cd, Cr and Zn were 14 to 33, 4 to 12, and 5 to 17% in glassy fish, and 10 to 26, 4 to 19, and 11 to 31% inmudskipper, respectively. Routes of radiolabeling in copepod prey did not affect metal AEs in either mudskipper or glassy, whereas metal AEs differed by up to 10-fold in glassy fish feeding on Artemia larvae labeled from different routes. There waslittle difference in the gut passage time of metals for different food types and metals or between fishes. AE was not significantly related to metal gut passage time or metal distribution in the soft tissues of zooplankton prey, for each metal. However,AE in mudskippers was significantly correlated with metal distribution in the prey¹s soft tissues when all 3 metals were considered. Our study demonstrated that marine fishes can appreciably assimilate trace metals, and trophic transfer should beconsidered as a source for metal accumulation in fishes.